the chandra view of nearby x-shaped radio galaxiesmiller/reprints/hodges10a.pdffainter pair of wings...

The Astrophysical Journal 7101205ndash1227 2010 February 20 doi1010880004-637X71021205Ccopy 2010 The American Astronomical Society All rights reserved Printed in the USA

THE CHANDRA VIEW OF NEARBY X-SHAPED RADIO GALAXIES

Edmund J Hodges-Kluck1 Christopher S Reynolds

1 Chi C Cheung

23 and M Coleman Miller

11 Department of Astronomy University of Maryland College Park MD 20742-2421 USA

2 NASA Goddard Space Flight Center Code 661 Greenbelt MD 20771 USAReceived 2009 July 7 accepted 2009 December 16 published 2010 January 28

ABSTRACT

We present new and archival Chandra X-ray Observatory observations of X-shaped radio galaxies (XRGs) withinz sim 01 alongside a comparison sample of normal double-lobed FR I and II radio galaxies By fitting ellipticaldistributions to the observed diffuse hot X-ray emitting atmospheres (either the interstellar or intragroup medium)we find that the ellipticity and the position angle of the hot gas follow that of the stellar light distribution forradio galaxy hosts in general Moreover compared to the control sample we find a strong tendency for X-shapedmorphology to be associated with wings directed along the minor axis of the hot gas distribution Taken atface value this result favors the hydrodynamic backflow models for the formation of XRGs which naturallyexplain the geometry the merger-induced rapid reorientation models make no obvious prediction about orientation

Key words galaxies active ndash intergalactic medium

Online-only material color figures

1 INTRODUCTION

ldquoWingedrdquo and X-shaped radio galaxies (XRGs) are centro-symmetric subclasses of FanaroffndashRiley (FR) type I and IIradio galaxies (Fanaroff amp Riley 1974) which exhibit a secondfainter pair of wings lacking terminal hot spots in addition to thesymmetric double lobe structure seen in ordinary FR II galaxies(Leahy amp Williams 1984) These galaxies comprise up to 10of radio galaxies although the galaxies in which the length ofthe wings exceeds 80 of that of the primary lobes (ldquoclassicalrdquoXRGs) are a very small subset of radio galaxies (Leahy amp Parma1992 Cheung 2007) The primary lobes of these galaxies as inother radio galaxies are produced by a jet emanating from anactive galactic nucleus (AGN) which becomes decollimated asit propagates into and interacts with the surrounding mediumIn FR II radio galaxies the terminal shock where the jet ramsinto its environment is characterized by a radio hot spot (alsooften seen in the X-ray band eg Hardcastle et al 2004)which produces the so-called edge-brightened morphology Theabsence of these hot spots in the fainter wings of XRGs impliesthat they do not harbor an active jet although Lal amp Rao (2007)argue in favor of a dual-AGN origin in which the pairs of lobesemanate from separate unresolved AGN

The X-shaped morphology is of interest because two remark-ably disparate classes of models have been invoked to explain itThe first class is predicated on the reorientation of the jets eitherby realignment of the supermassive black hole (SMBH) spin orthe accretion disk whereas the second purports to explain thedistorted morphology as the result of hydrodynamic interactionbetween the radio lobe and its surrounding gaseous environmenton kiloparsec scales

In the first case the most common explanation for theX-shaped morphology is that the SMBH has its spin axisrealigned either via merger or precession The possibilitythat XRG morphology is produced by a SMBH merger is ofconsiderable interest as a potential estimate of merger ratesand hence source rates for the Laser Interferometer Space

3 Current address National Research Council Research Associate SpaceScience Division Naval Research Laboratory Washington DC 20375 USA

Antenna because fossil lobes will quickly decay due to adiabaticexpansion an XRG would be a sign of a recent merger In thisscenario (eg Rottmann 2001 Zier amp Biermann 2001 Merrittamp Ekers 2002) a SMBH binary formed by galactic mergerand dynamical friction hardens for an unknown length of timevia three-body interactions until gravitational radiation becomeseffective at radiating orbital energy At this point the binaryquickly coalesces and the radio jets realign along the directionof the angular momentum of the final merged black hole The jetbegins propagating in the new direction leaving a decaying pairof radio lobes along the old spin axis A significant objectionto the merger model (Bogdanovic et al 2007) is that the linearmomentum ldquokickrdquo imparted to the coalesced SMBH can exceedseveral times 103 km sminus1 if the spins of the black holes arerandom at the time of merger sufficient to escape the galaxyCo-aligned spins reduce the magnitude of the kick but wouldnot result in an X-shaped source Although not a problem forrapid reorientation models which rely on precession or otherrealigning mechanisms (Ekers et al 1978 Rees 1978 Kleinet al 1995 Dennett-Thorpe et al 2002) an additional objectionto the ldquofossilrdquo lobe scenario is that the secondary lobe lengths insome XRGs are inconsistent with the fast lobe decay expectedwhen a jet changes alignment (Saripalli amp Subrahmanyan 2009hereafter S09)

In contrast to the rapid-realignment models hydrodynamicmodels propose that the wings of XRGs were never directlyinflated by a jet These models argue that XRGs form dueto backflow (plasma flowing back toward the AGN from thehot spot shocks) that interacts with the surrounding gas Aspresently conceived backflow models require FR II morphologyto drive the strong backflows The existence of FR I XRGschallenges these hypotheses but S09 argue that since severalof the FR I XRGs appear to be restarted AGN with innerFR II morphology the FR I XRGs could have had edge-brightened morphology when the wings were inflated implyingan evolution of FR II to FR I sources (Cheung et al 2009) In thispaper we consider the backflow models as a unified class Thetwo most prominent backflow scenarios include the ldquobuoyantbackflowrdquo model (Leahy amp Williams 1984 Worrall et al 1995)and the ldquooverpressured cocoonrdquo model (Capetti et al 2002

1205

1206 HODGES-KLUCK ET AL Vol 710

hereafter C02) The buoyant backflow model supposes that thebuoyancy of the relativistic plasma cocoon in the interstellar orintragroupintracluster medium (ISM or IGMICM) producesthe additional wings Because of the collimation seen in the moredramatic XRG wings we refer to them hereafter as ldquosecondarylobesrdquo even though if the hydrodynamic premise is correct theyare not of the same character as the primary lobes

C02 propose a variant model in which backflowing plasmaconfined by an envelope of hot gas continues to aggregate untilthe cocoon of radio plasma is significantly overpressured atwhich point it blows out of the confining medium at its weakestpoint Supposing that the confining medium is the ISM of anelliptical galaxy if the jet is aligned along the major axis ofthe galaxy then the cocoon may become overpressured beforethe jet bores through the ISM and the radio plasma will blowout along the minor axis of the galaxy forming the secondarylobes Conversely if the jet is oriented along the minor axis ofthe galaxy then backflow will either escape along the same axisor the jet will escape the ISM before the cocoon can becomeoverpressured C02 cite an intriguing correlation between theorientation of the secondary lobes in XRGs and the minor axisof the host galaxy as evidence for their model which they furthersupport with two-dimensional hydrodynamic simulations In afollow-up study including ldquonormalrdquo radio galaxies S09 findthat the primary lobes of giant radio galaxies are preferentiallyaligned along the minor axis of the host whereas they extendthe original C02 result to a larger XRG sample Althoughthe observed geometric correlation is strong much of thepotentially relevant physics is absent in the C02 simulationsand Kraft et al (2005) note that the buoyant backflow modelcan explain the observed correlation by assuming an anisotropicmedium to divert the backflow Moreover it is unclear whetherreal radio lobes are actually overpressured Reynolds et al(2001) argue that an overpressured cocoon is inflated early onbut in the buoyant backflow model the secondary lobes areformed later In either case the geometric correlation favors ahydrodynamic origin for the secondary lobes in the absence ofan explanation for a relationship between the angular momentaof two merging SMBHs and large-scale structure of the galaxyFor the remainder of this paper we refer to the ldquoC02 geometryrdquoto describe the correlation noted in XRGs and the proposedgeometry of jet alignment that would produce them

There are additional XRG formation models which aresimilar to the ones presented above in that they rely solely oneither the black hole(s) involved or jetndashgas interaction Theseinclude the hypothesis that X- and Z-shaped distortions arise viagravitational interaction with another galaxy (Wirth et al 1982van Breugel et al 1983) the idea that the jets are diverted by theISM of a smaller merging galaxy (Gopal-Krishna et al 2003Zier 2005) and the aforementioned Lal amp Rao (2007) proposalthat both lobes are powered by active jets Because these modelsare not as easily probed by the hot gas we focus on the backflowmodels hereafter

In this paper we seek to characterize the properties of the hotgas in these systems and determine whether the C02 opticalndashradio geometric correlation also exists in the X-ray band Oneassumption of the C02 proposal is that the stellar distributiontraces the hot gas which makes up the confining medium Wewill test this assumption directly by determining the extent towhich optical and X-ray morphology are correlated As a paral-lel study we present the results from new and archival ChandraX-ray Observatory observations of XRGs and investigatewhether the hot gas in XRG systems differs from that in a

comparison sample of archival Chandra observations of ldquonor-malrdquo FR I and II galaxies (taken largely from the 3CRR catalogLaing et al 1983)

Any observational study of XRGs is necessarily limited bythe small number of known and candidate sources Our studyis further limited by two important factors (1) the hot gas sur-rounding radio galaxies becomes increasingly difficult to char-acterize at higher redshift and (2) useful X-ray data do not existfor most XRGs These considerations strongly constrain ourconclusions We therefore discuss in detail our target selectioncriteria in Section 2 as well as the observational parametersand reduction techniques applied to the data In Section 3 wediscuss our primary analysis of the morphology of the hot gasand in Section 4 we discuss the X-ray spectra of the AGN InSection 5 we summarize our results and interpretations

Throughout this paper we adopt the Wilkinson MicrowaveAnisotropy Probe (WMAP) values of H0 = 71 km sminus1 Mpcminus1ΩM = 027 and Ωvac = 073 with flat geometry We calculateequivalent angular scale and distances at redshift using theonline calculator provided by Wright (2006) and for Galacticabsorption we use the online HEASARC NH calculator withvalues from the LeidenArgentineBonn survey (Kalberla et al2005)4

2 CHANDRA OBSERVATIONS

Chandra is well suited to a study of the hot environmentsof radio galaxies thanks to its high sensitivity 0primeprime5 spatialresolution and 03ndash10 keV bandwidth Chandra has also beenable to resolve X-ray emission associated with the radio lobesinto hot spots and jets (Hardcastle et al 2004) distinguishingthis emission from the gaseous halos is especially important forour purposes

Our analysis sample of Chandra data consists of 18 compari-son sample galaxies and 8 XRGs (Figures 1 and 2 with observa-tional parameters in Table 1) In this section we describe howwe arrived at this sample starting with the preliminary selec-tion criteria for the XRG and comparison samples from radiodata and availability in the Chandra archive (Section 21) Afterreducing these data we rejected a number of galaxies due tolow quality or pileup (Section 22) then used spectral fitting tofind those galaxies where the diffuse gas dominates the photoncount in the relevant regions (Section 23) These are the galax-ies we include in our final sample (Table 1) Figures 1 and 2are discussed along with the radio and optical data we use inSection 24

We note that many of the archival data sets have been pub-lished and references are provided in Table 1 where availableOur goal is not to exhaustively study any individual sourceNotes on individual sources are found in the Appendix

21 Preliminary Target Selection

The most complete compilation of known and candidateX-shaped sources in the literature is that of Cheung (2007)who used the NRAO5 Very Large Array (VLA Thompson et al1980) Faint Images of the Radio Sky at Twenty cm (FIRSTBecker et al 1995) data to identify the candidate XRGs Forthis paper we define XRGs as comprising all radio galaxies inCheung (2007) that have a wing length exceeding 80 of the

4 See httpheasarcgsfcnasagovcgi-binToolsw3nhw3nhpl5 The National Radio Astronomy Observatory is a facility of the NationalScience Foundation operated under cooperative agreement by AssociatedUniversities Inc

No 2 2010 THE CHANDRA VIEW OF NEARBY X-SHAPED RADIO GALAXIES 1207

Figure 1 Chandra and optical images of our control sample galaxies with significant thermal emission The left panel in each case is an image of the ChandraACIS-S3 chip with uniform Gaussian smoothing and point sources removed The right image is an optical image from DSS or SDSS Overlaid in blue are VLA radiomap contours The images are sorted by ascending redshift Note that for 3C 98 and 3C 388 the chip image is of the ACIS-I chip(s) instead of ACIS-S3

(A color version of this figure is available in the online journal)


Figure 1 (Continued)

active lobes (Leahy amp Parma 1992 the ldquoclassicalrdquo XRGS) andthose ldquowingedrdquo sources in Cheung (2007) which have obviousX-shaped morphology in the angle between the active lobes andthe wings Assuming the projected lengths on the sky are thereal lengths of the wings in the backflow models these may beldquoclassicalrdquo XRGs at an earlier stage

We wish to study the hot gas surrounding the radio galaxyThe rapid decline in surface brightness and reduction in angularsize with increased redshift makes a cutoff redshift of z sim 01practical for typical Chandra exposure times (even in thisscheme our sample is biased toward high pressure systems)Nineteen XRGs fall within this cutoff the highest redshift inthis group is z = 0108 However we have Chandra data foronly 13 of these sources and these comprise our preliminarysample These sources include 3C 315 3C 2231 NGC 326PKS 1422+26 3C 433 3C 403 3C 192 B2 1040+31A Abell1145 4C +0058 3C 1361 4C +3225 and 4C +4829

This sample is heterogenous in its radio properties andmorphology A few of the galaxies may be described as Z-shaped(Gopal-Krishna et al 2003 Zier 2005) NGC 326 for instancehas long secondary lobes that do not seem to meet at a commoncenter Others (eg B2 1040+31A) have obviously X-shapedlobe axes but the lobes are not as well collimated as in NGC 326or 3C 315 Lastly PKS 1422+26 B2 1040+31A and 3C 433appear to be hybrid FR III radio galaxies with one FR I lobeand one FR II lobe (A ldquoHYMORrdquo see Gopal-Krishna amp Wiita2000) It is unknown whether these distinctions are signaturesof any formation model and we note that XRGs tend to lie closeto the FR III break in other observables (Cheung et al 2009)

In this paper we use the definitions of Cheung (2007) and soconsider the XRG sample as a unified whole and we caution thatour results are interpreted within this framework In particularthere is no consensus in the literature on what constitutes an ldquoXrdquo-shaped galaxy In their optical study for example S09 classify3C 761 (z = 0032) as an XRG whereas we do not They alsoclassify several higher redshift galaxies as XRGs which do notappear in the Cheung (2007) list (eg 3C 401 or 3C 438) inthis respect our sample is conservative At least one high-redshiftXRG from the Cheung (2007) listmdash3C 52 (z = 0285)mdashhas aChandra exposure and 3C 1971 (z = 0128) may be an XRGand is also in the Chandra archive We choose not to use theseexposures although we note them in Appendix A3

Within the same redshift cutoff we identify normal FR I andII galaxies in the Chandra archive as a comparison sample Theaim of this sample is to determine whether XRGs systematicallydiffer in X-ray properties from normal radio galaxies It is notobvious what constitutes an appropriate comparison samplebecause although FR II lobes are deemed necessary to produceX-shaped morphology in the backflow scenario FR I XRGsexist (S09) In the S09 interpretation of FR I XRGs the FR Ilobes must have had FR II morphology at the time the wingswere generated Supposing that both the C02 model and S09interpretation are correct the ldquooldrdquo FR I lobes must obeythe same geometry as their ldquoactiverdquo FR II counterparts Acomparison of the XRG sample to both types is thereforeuseful The combined sample also provides a larger reservoirof sources for measuring the correlation between optical andX-ray isophotes in the ISM We adopt a preliminary comparison


Figure 2 Chandra and optical images of our XRG sample galaxies with significant thermal emission The left panel in each case is an image of the Chandra ACIS-S3chip with uniform Gaussian smoothing and point sources removed The right image is an optical image from DSS or SDSS Overlaid in blue are VLA radio mapcontours The images are sorted by ascending redshift


sample consisting of (1) all FR II galaxies within z sim 01with data in the Chandra archive and (2) FR I galaxies fromthe DRAGN catalog6 with the same conditions There are 41sources meeting these criteria

6 Leahy JP Bridle AH amp Strom RG editors ldquoAn Atlas of DRAGNsrdquo(httpwwwwjbmanacukatlas)

22 Data Reduction

Thirteen XRGs and 41 normal radio galaxies comprise ourpreliminary samples but the data for many of these are not ofsufficient quality for our analysis Both the archival data and ournew data use Advanced CCD Imaging Spectrometer7 (ACIS)

7 See httpcxcharvardeduproposerPOGpdfACISpdf


Table 1Chandra Observational Parameters

Name Secondary Identifier z Ang Scale Obs IDs Exp Time CCD Array FR Type Selected Chandra Refs Radio Refs(kpcprimeprime) (ks)

XRGs

B2 1040+31A J1043+3131 0036 0706 9272 10 ACIS-S III This work AM221+AM222PKS 1422+26 J1424+2637 0037 0725 3983 10 ACIS-S III This work AM364NGC 326 J0058+2651 0048 0928 6830 94 ACIS-S III 1 2 9 10 a3C 403 J1952+0230 0059 1127 2968 49 ACIS-S II 3 4 5 b4C +0058 J1606+0000 0059 1127 9274 10 ACIS-S II This work AC8183C 192 J0805+2409 0060 1144 9270 10 ACIS-S II 6 c3C 433 J2123+2504 0102 1855 7881 38 ACIS-S III 7 b3C 315 J1513+2607 0108 1951 9313 10 ACIS-S I This work AM364

Comparison sample

3C 449 J2229+3921 0017 0341 4057 30 ACIS-S I 4 5 8 9 10 25 AK3193C 31 J0107+3224 0017 0341 2147 45 ACIS-S I 4 5 9 11 25 a3C 831B J0318+4151 0018 0361 3237 95 ACIS-S I 4 5 12 AK4033C 264 J1145+1936 0021 0419 4916 38 ACIS-S I 4 8 d3C 66B J0223+4259 0022 0439 828 45 ACIS-S I 4 5 8 13 e3C 296 J1417+1048 0024 0477 3968 50 ACIS-S I 4 5 fNGC 6251 J1632+8232 0024 0477 4130 50 ACIS-S III 4 14 gPKS 2153minus69 J2157minus6941 0028 0554 1627 14 ACIS-S II 15 16 h3C 338 J1628+3933 0030 0593 497+498 20+20 ACIS-S I 4 5 8 9 14 17 i3C 98 J0358+1026 0030 0593 10234 32 ACIS-I II This work j3C 465 J2338+2702 0031 0612 4816 50 ACIS-S I 4 8 9 26 a3C 293 J1352+3126 0045 0873 9310 8 ACIS-S II 6 kCyg A J1959+5044 0056 1073 360+5831 35+51 ACIS-S II 18 19 j3C 445 J2223minus0206 0056 1073 7869 46 ACIS-S II 26 l3C 285 J1321+4235 0079 1474 6911 40 ACIS-S II 20 k3C 452 J2245+3941 0081 1508 2195 81 ACIS-S II 4 21 b3C 227 J0947+0725 0087 1609 6842+7265 30+20 ACIS-S II 22 b3C 388 J1844+4533 0091 1675 4756+5295 8+31 ACIS-I II 23 m

Notes Observational parameters for archival and proprietary Chandra data sets with significant thermal emission (see Table 3) Redshifts are obtainedeither from SIMBAD or compilation of Cheung (2007) X-ray references with more detail on the particular data set are provided above not all referencesare provided VLA program codes are provided where we processed data ourselvesReferences X-ray (1) Worrall et al 1995 (2) Murgia et al 2001 (3) Kraft et al 2005 (4) Evans et al 2006 (5) Balmaverde et al 2006 (6) Massaroet al 2008 (7) Miller amp Brandt 2009 (8) Donato et al 2004 (9) Canosa et al 1999 (10) Worrall amp Birkinshaw 2000 (11) Jeltema et al 2008(12) Sun et al 2005 (13) Hardcastle et al 2001 (14) Evans et al 2005 (15) Ly et al 2005 (16) Young et al 2005 (17) Johnstone et al 2002(18) Young et al 2002 (19) Smith et al 2002 (20) Hardcastle et al 2007b (21) Isobe et al 2002 (22) Hardcastle et al 2007a (23) Kraft et al 2006(24) Sun et al 2009 (25) Perlman et al 2010 (26) Hardcastle et al 2005Radio (a) Condon et al 1991 (b) Black et al 1992 (c) Baum et al 1988 (d) NRAO VLA Archive Survey (e) Hardcastle et al 1996 (f) Leahy ampPerley 1991 (g) Sambruna et al 2004 (h) Fosbury et al 1998 (i) Ge amp Owen 1994 (j) Perley et al 1984 (k) Alexander amp Leahy 1987 (l) Leahyet al 1997 (m) Roettiger et al 1994

chips with no transmission grating in place we immediatelyrejected sources which have only grating spectrometer observa-tions due to severe pileup in the zeroth-order image (only thebrightest sources have grating data) Most of the data sets usethe nominal aim point on the ACIS-S3 chip but we considerseveral ACIS-I archival observations

We reprocessed the Chandra data sets to generate 03ndash10 keV level = 2 files using the Chandra Interactive Anal-ysis of Observations (CIAO v40) data processing recipes(ldquothreadsrdquo)8 with the most recent CALDB release (350) Timeswith noticeable background flares were excised by inspecting03ndash10 keV light curves A few comparison sample data setscontained the readout streak produced by bright sources whichwe replaced following the CIAO thread with a strip of nearbybackground on either side of the central point source Thebright sources NGC 6251 and 3C 264 were observed in a18-size subarray mode of the ACIS-S3 chip but still produceda readout streak Exposure-corrected final images were then

8 See httpcxcharvardeduciaothreadsindexhtml

produced from the energy-filtered level = 2 files following thestandard CIAO thread using the aspect solution file associatedwith each observation

The core AGN X-ray emission was identified by matchingthe position of the X-ray source with the optical counterparton the sky More accurate positions were determined by binningthe X-ray image and calculating the centroid

23 Spectral Extraction

Our analysis (Section 3) is based on the properties and mor-phology of the ISM and IGMICM Therefore we reject galax-ies from our preliminary sample where we do not detect strongextended thermal plasma We determine the final sample in twosteps (1) we use radial profile fitting to reject sources with noextended emission and distinguish between multiple compo-nents of extended emission in the remainder We extract spectrafrom regions corresponding to these extended components then(2) reject sources whose extended emission is not fitted well bystrong thermal components We describe the first step presentlyand the second in Section 24


Extended emission on the chip may be made up of multiplesources We use surface brightness profile fitting to distinguishbetween these sources and based on these fits define regions forspectral extraction to isolate each source as much as possible Weexcised point sources from the level = 2 file then extracted andfit radial profiles from annuli surrounding the AGN out to manykpc (scale depends on z) In many cases no diffuse emissionwas detected above background Where multiple componentswere found we defined spectral extraction apertures based onthe characteristic radii (r0 from a β model) for each regionCompact emission centered on the AGN with r0 smaller than thehost galaxy we identified as ldquoISMrdquo whereas very broad emissionwhich declines slowly in surface brightness we identified withthe ldquoIGMICMrdquo These are the labels used in Table 3 we notethat the only sources included in Table 3 are those in whichthermal emission has been verified At the present stage thepurpose of these regions is solely to isolate different sources forspectral fitting

For the larger dimmer extended sources the fits (and hencer0) were less reliable However the slow decline of the ldquoIGMrdquosurface brightness means the spectra we extract are relativelyinsensitive to the size and shape of the region Crucially thespectral extraction apertures are not the same as those we usefor our analysis in Section 3 and are defined only to isolatedifferent sources Spectra were extracted from these regions andwere binned to at least 15 photons per bin to ensure the reliabilityof the χ2 statistic in high-quality spectra the binning was ashigh as 100 In addition we extract spectra for the unresolvedAGN emission from detection cells using the 90 encircledenergy radius as determined by the CIAO mkpsf tool We returnto the AGN spectra in Section 4

24 Detection of Diffuse Gas

We fit models to the spectra we extracted (Section 23)to determine whether the emission is dominated by thermalplasma Specifically our sample consists of those galaxiesin which the thermal emission surrounding the AGN appearsdominant in number of photons a point we return to belowWe first ascertain the presence of hot gas by fitting the spectraextracted from each source using XSPEC v1250j (Arnaud1996) In this paper we exclusively use the apec model Thisstep is required since extended emission need not be thermalin originmdashplausible nonthermal sources include power-lawemission from the boundary shock of the cocoon inflated by theradio jets or from X-ray binaries (XRBs) in the host galaxy Ourfits all use a frozen Galactic NH absorption component Afterthermal emission is established we then require the thermalcomponent to be dominant at low energies This ensures thatthe main contribution to the (energy-filtered) surface brightnessis the thermal plasma Of course the hot atmospheres of manygalaxies in our sample have been well studied (eg by ChandraTable 1) but we wish to apply a uniform standard to all oursources including ones which have low signal

For each spectrum we first determine whether a single power-law or thermal model is a better baseline fit based on theχ2 statistic then add complexity as the degrees of freedomallow In the case of thermal models we begin by freezingthe abundances with an isothermal model (there exists anabundancemdashnormalization degeneracy in the absence of strongemission lines) Two-temperature (2-T) or multi-T models areinvoked if an isothermal model is insufficient to fit the spectrumand the additional thermal component produces a better fit thana power-law component It is worth asking whether a spectrum

fitted well by a single thermal model is better fitted by a blendof power-law and thermal components The answer is almostinvariably ldquonordquo In very low signal spectra with few degrees offreedom we conclude hot gas is present if a thermal model withreasonable parameters (kT lt 50 and 01 lt Z lt 10) is abetter fit than a power-law model We justify this assumption bythe slopes of soft spectra unabsorbed power-law emission tendsnot to fall off at the lowest energies whereas thermal emissionpeaks near 10 keV A ldquopeakyrdquo spectrum even a low-signal oneis fitted better by a thermal model As described in Section 23we have attempted to isolate different sources but we see theISM and IGM in projection We usually lack the signal for adeprojection analysis so we first extract and fit a spectrum fromthe larger IGM region then add the resultant models as frozencomponents in the ISM spectrum (keeping the normalizationthawed) We find this produces better results than using a ringof IGM as background for the ISM spectra It is possible that thepower-law models are in fact describing thermal continua butthe thermal models which fit these spectra have inordinately hightemperatures and often require suspiciously low abundances

For a galaxy to be included in our final sample we required thethermal component to be dominant between 03 keV lt kT lt2 keV Due to Chandrarsquos energy-dependent effective area evencomponents with higher luminosity (eg an absorbed powerlaw) may have many fewer photons in this range This criterionallows us to characterize the morphology of only the hot plasma

Up to this point we have treated our sources as uniformly aspossible Our analysis sample consists of the galaxies whoseextended emission is dominated by thermal plasma but wealso reject sources with very complex morphology (3C 321M84 M87 and 3C 305 Cyg A was retained after excising theinner cocoon) We remind the reader that we began with anXRG sample comprising those 13 galaxies within z sim 01 withdata in the Chandra archive Of these we have eight in ouranalysis sample The preliminary comparison sample included41 normal radio galaxies within the same cutoff and of thesewe retain 18 (10 of which are FR II galaxies) Unfortunatelyin many of the shorter XRG observations we failed to detectsignificant diffuse emission Notes on individual galaxies arein the Appendix including those XRGs not included in ouranalysis sample (Appendix A3) Sources we considered butrejected are listed in Table 2

For those galaxies in our analysis sample we provide themodel fit parameters in Table 3 We also present the emission-weighted density n and average pressure P = nkTfit n wascomputed by assuming the minor axis of the extraction regionon the sky is the true minor axis and that the ellipsoid isaxisymmetric in the minor axis (ie the axis along the lineof sight is the minor axis) We report errors in Table 3 forone parameter of interest at Δχ2 = 27 (90) but we do notreport errors on n or P since there are unquantifiable sourcesof systematic error from our assumptions on the volume Theaverage densities and pressures are not particularly useful forstudying any one system because profile information has beendiscarded for most of our sources we cannot use deprojectionOur spectra with folded model fits are shown in Figures 3 (ISM)4 (IGM) and 5 (AGN)

25 Radio and Optical Maps

We require high signal and high-resolution radio data in or-der to study the interaction between the radio lobes and theX-ray emitting gas As the secondary lobes of XRGsare typically much fainter than the hot spots demarcating


Table 2Rejected Chandra Observations

Name z Obs IDs Exp Time Obs Type Reason(ks)

XRGs

4C +3225 0052 9271 10 ACIS-S a4C +4829 0053 9327 10 ACIS-S a3C 1361 0064 9326 10 ACIS-S aJ1101+1640 0068 9273 10 ACIS-S Mispointing3C 2231 0107 9308 8 ACIS-S a

Archival normal radio galaxies

M84 0003 803 + 5908 + 6131 29 + 47 + 41 ACIS-S bM87 0004 352 + 1808 38 + 14 ACIS-S b3C 84 0018 333 + 428 27 + 25 HETGS b+pileup3C 442A 0026 5635 + 6353 + 6359 + 6392 29 + 14 + 20 + 33 ACIS-I b3C 353 0030 7886 + 8565 72 + 18 ACIS-S c3C 120 0033 3015 + 5693 58 + 67 HETGS+ACIS-I cDA 240 0036 10237 24 ACIS-I a3C 305 0042 9330 8 ACIS-S b3C 3903 0056 830 34 ACIS-S c3C 382 0058 4910 + 6151 55 + 65 HETGS c+pileup3C 33 0059 6910 + 7200 20 + 20 ACIS-S c3C 35 0067 10240 26 ACIS-I a0313minus192 0067 4874 19 ACIS-S c3C 105 0089 9299 8 ACIS-S a3C 326 0090 10242 + 10908 19 + 28 ACIS-I Target not on chip3C 321 0096 3138 48 ACIS-S b3C 236 0099 10246 + 10249 30 + 41 ACIS-I c3C 327 0104 6841 40 ACIS-S c4C +7426 0104 4000 + 5195 38 + 32 HETGS c3C 1841 0118 9305 8 ACIS-S a

Notes Galaxies were selected for the preliminary sample as described in Section 21 and rejected for lack ofdiffuse gas or prohibitively complex morphology for our analysis (eg obvious multiple bubbles)a No diffuse emission detectedb Complex morphologyc No diffuse thermal emission detected

the terminal shocks of the active lobes deep radio observationsare often required to accurately determine their extent and angu-lar offset from the active pair The VLA is ideal for continuumband observations Reduced VLA data for many of the sourcesare available through the NASAIPAC Extragalactic Database(NED) references are provided in Table 1 where available Insome cases we have reprocessed archival VLA data ourselvesand these are noted in Table 1

In contrast to the requirement for high-quality radio data(needed to constrain the orientation of the radio jets and lobes)images from the (Palomar or UK Schmidt Telescope) DigitizedSky Survey (DSS) are usually sufficient for comparing theextent and alignment of the diffuse X-ray emitting gas tothe distribution of optical light Except in the case of B21040+31A a close triple system the optical emission on therelevant scales does not have significant contamination fromcompanion sources We note that the DSS spans our entiresample whereas the higher resolution Sloan Digital Sky Survey(SDSS Adelman-McCarthy et al 2008) data are available forfewer than half of our sources However we compare the DSSimages to the SDSS images where available and note that goodagreement is found in most cases for our model parameters(Section 32 Table 5) We also use published Hubble SpaceTelescope (HST) images in particular those of Martel et al(1999) for 3CR galaxies within z lt 01 However this surveyis not sufficiently complete to replace the DSS data

The images in Figures 1 and 2 show the data using thehigher quality SDSS images for the optical band where pos-sible Because of the differences in scale between radio galaxiesand the different media which are important for lobendashgas in-teraction the chip images we show are all processed slightlydifferently In most cases they have been smoothed with aGaussian kernel of fixed σ (per galaxy) to enhance diffuse emis-sion Adaptive smoothing sometimes produces artificial struc-ture in our images and is not used Overlaid on the images ofthe ACIS chips are radio contours and accompanying eachX-ray image of the optical field on the same spatial scaleFigures 1 and 2 have been processed to represent the ap-pearance of the sources and distribution of surface bright-ness on the sky but we did not use these images directlyin our analysis In addition the varying signal-to-noise ra-tios (SNs) in X-ray images do not necessarily correspondto real variation in source luminosity because the data setscome from observations of varying depth and redshift Be-cause some of the observations are shallow (10 ks) or usethe ACIS-I array a non-detection of diffuse emission is notconclusive

3 THERMAL ATMOSPHERE PROPERTIESThe models which assert that XRGs result from the interac-

tion of the radio lobes with anisotropic gaseous environments(Capetti et al 2002 Kraft et al 2005) must ultimately be tested


Table 3Thermal X-ray Spectral Parameters

Galaxy Region a b z Gal NH kT z n P Models LXth χ2dof(kpc) (kpc) (1020 (keV) (10minus3 (10minus11 (1041

cmminus2) cmminus3) dyne cmminus2) erg sminus1)

XRGs

B2 1040+31A ISM 5 5 0036 167 16 plusmn 04 03 (f) 38 97 apec 16 4665

IGM (s) 25 25 18 plusmn 02 10 (f) 38 11 apec 32 10911

IGM (l) 75 75 13+03minus01 03+04

minus02 11 024 apec 47 20223

PKS 1422+26 IGM 85 40 0037 154 089 plusmn 009 03+02minus01 20 029 apec+PL 52 23120

NGC 326 ISM 6 6 0048 586 068 plusmn 005 10 (f) 28 30 apec(+IGM) 54 13317

IGM 166 94 36 plusmn 04 08 (f) 19 11 apec 10 941100

3C 403 ISM 9 6 0059 122 024 plusmn 003 10 (f) 23 089 apec+PL+NH(gauss+PL) 10 100794

IGM 97 40 06 plusmn 02 10 (f) 037 004 apec 09 34336

4C +0058 ISM 17 17 0059 714 12 plusmn 02 10 (f) 73 20 apec 30 586

3C 192 ISM+IGM 19 19 0060 408 10+22minus02 10 (f) 49 079 apec+NH(PL) 25 395

3C 433 ISM+IGM 44 26 0102 777 096 plusmn 01 10 (f) 28 11 apec+PL+gauss 40 162123C 315 IGM 200 110 0108 428 06+04

minus01 10 (f) 10 01 apec+PL 82 4510

Comparison sample

3C 449 ISM 5 5 0017 899 077 plusmn 009 10 (f) 15 19 apec(+IGM) 022 21119

IGM 32 32 158 plusmn 006 08 plusmn 02 29 073 apec 39 1798169

3C 31 ISM 4 4 0017 536 068+004minus003 10 (f) 22 24 apec(+IGM) 034 47058

IGM 30 30 20+05minus02 04+02

minus01 20 069 apec 13 1431138

3C 831B ISM 3 3 0018 134 065 plusmn 004 10 (f) 34 36 apec(+IGM) 013 30135

ICM 56 30 8+6minus3 10 (f) 12 16 apec 17 80986


3C 66B ISM 9 9 0022 767 061+006minus004 03+1

minus01 72 071 apec(+IGM) 036 49842


IGM 75 75 4+4minus1 10 (f) 08 05 apec 08 18219


PKS 2153minus69 ISM 7 7 0028 559 077 plusmn 007 10 (f) 10 12 apec(+hot IGM) 14 26024

IGM 32 32 T1 = 30+2minus1 10 (f) 26 13 apec+apec 68 41842

T2 = 09 plusmn 006 10 (f)

3C 338 ICM 30 30 0030 089 T1 = 18+02minus01 07 plusmn 005 28 17 apec+apec 434 4325390

T2 = 50+1minus05 07 plusmn 005

3C 98 IGM 46 31 0030 108 11+03minus02 02+04

minus01 18 032 apec 08 8511


IGM 80 56 42+05minus03 10 (f) 23 16 apec+gauss 25 1768164


Cyg A ICM 140 140 0056 302 Tlow = 32+13minus01 06 (f) 48 60 cflow 1600 4331403

Thigh = 18 plusmn 7

3C 445 IGM 73 54 0056 451 07+03minus04 10 (f) 026 003 apec+PL 06 93814

3C 285a ISM+IGM 30 30 0079 127 T1 = 12+04minus02 10 (f) 23 013 apec+apec 29 697

T2 = 033+03minus005 10 (f)

3C 452 IGM 201 82 0081 964 38 plusmn 01 10 (f) 13 079 apec+PL 50 1487155

3C 227 ISM+IGM 28 28 0087 211 T1 = 02 (f) 10 (f) 59 10 apec+apec+gauss 74 12729

T2 = 12+03minus02 10 (f)

3C 388 ICM(bar) 16 16 0091 558 24 plusmn 02 10 (f) 24 92 apec 41 38940

ICM(big) 130 130 33 plusmn 01 10 (f) 31 17 apec 425 1749200

Notes Diffuse atmosphere spectral parameters for targets in Table 1 (f) denotes a frozen parameter In calculating n we assume axisymmetry and use a volumeV = ab2 Unabsorbed luminosities are reported for the thermal component only in the case of the ISM this is the cooler component The notation (+IGM) indicatesthat a thermal model with all parameters except the normalization frozen was used in the fit these parameters are based on fits to the IGMa 3C 285 is difficult to disentangle but the larger IGM values agree with those coincident with the ISM

by direct observations of these environments In particular wewish to know whether the correlation described in C02 exists inthe X-ray band ie whether XRGs are preferentially found insystems where the jets are directed along the major axis of thegas distribution

This objective can be distilled into two distinct questionsFirst the observed correlation between the XRG secondarylobes and the minor axis of the host galaxy was taken byC02 to imply that the minor axis of the ISM in these galaxieswas similarly aligned But how well does the X-ray gas trace


Figure 3 Spectra of the X-ray ISM we use in our morphology comparison (Table 5) The XRG sample is shown with galaxy names in green and the total model fithas been plotted over the data in red The values can be found in Table 3 Note that 3C 403 is shown in Figure 5 since the ISM is small compared to the PSF and isisolated via energy filtering (Kraft et al 2005)


the optical isophotes Second is there a systematic differencebetween the orientation of the radio lobes and the X-ray gasdistribution in XRGs and normal radio galaxies In other wordsdoes the C02 correlation exist in the media which interact withthe radio lobes These questions are distinct in part becausethe medium responsible for shaping the XRGs in the backflow

models is not necessarily the ISM but may be the IGMICM Because these questions rely on our measurement ofgas morphology we first describe our image fitting methodwhich consists of fitting ellipses to measure ellipticity (ε equiv1 minus ba) and position angle (PA) of the X-ray emission onthe sky


Table 4Optical Hosts Comparison

Name εDSS PADSS PAradio

This Work C02 S09 This Work C02 S09 This Work C02 S09

Working Sample

B2 1040+31A 015 153 159

PKS 1422+26 016 118 92

NGC 326 004 0 153 b 120 1353C 403 027 a 025 39 35 39 72 85 794C +0058 051 139 65

3C 192 002 a 0 119 95 b 123 125 1233C 433 030 047 167 145 169 1643C 315 037 a 046 44 35 33 12 10 8

Unused XRGs

4C +3225 012 a 015 90 90 84 61 60 644C +4829 003 0 127 b 179 1703C 1361 039 a 037 101 100 117 106 110 139J1101+1640 034 029 62 64 113 1143C 2231 042 a 045 43 40 40 7 15 15

Notes A ldquo middot middot middot rdquo signifies no data exist in the literature for comparison Notethat while radio position angles are generally in agreement large discrepanciesexist (attributable to where the jetlobe PA is measured) Uncertainties are notquoted in C02 or S09a Capetti et al (2002) do not provide ε values in their paperb Saripalli amp Subrahmanyan (2009) do not report an optical PA if ε is ldquo0rdquo

31 Ellipse Fitting

We determine the gross morphology of the hot gas by fittingellipses to the X-ray emission and finding the characteristicε and PAmdashgross elongation and orientationmdashof the surfacebrightness We treat the surface brightness as a two-dimensionalldquomassrdquo distribution and compute the moment of inertia tensorwithin an aperture chosen by the scale of the medium (a pointwe return to below) From this we measure the principal axescorresponding to the characteristic major and minor axes ofthe distribution Of course the gas distribution may well havecomplexity beyond that captured by a simple elliptical modelmdashhowever most of our data do not justify higher-order modelsWe describe our method presently

Our generic ellipse-fitting routine takes as input a processedsurface brightness distribution on the chip (see below) Todetermine the principal axes we use the QL method withimplicit shifts (Press et al 1992) to find the eigenvalues ofthe tensor whereas the PA is determined by the orientationof one of the eigenvectors We use the IDL eigenql function9

realization of this method The QL method with implicit shifts isa method for finding the eigenvalues of a matrix by decomposingit into a rotation matrix ldquoQrdquo and a lower triangular matrix ldquoLrdquoby virtue of the decomposition the eigenvalues of the originalmatrix appear on the diagonal of the lower triangular matrix atthe end To determine the 2σ error bars reported in Table 5 weuse the bootstrap resampling method over 104 iterations (Efron1982) We adopt this method since it is better suited to low countrate images than the standard Sherpa10 two-dimensional fittingroutines

Our treatment of the surface brightness prior to the fittingdescribed above differs slightly between the bright and compact

9 Source code available fromhttpimac-252astanfordeduprogramsIDLlibeigenqlpro10 See httpcxcharvardedusherpa

ISM and the faint extended IGMICM Within each regimewe attempt to treat each data set uniformly any additionalprocessing is noted in the Appendix

1 Interstellar medium For the ISM we use no additionalbinning beyond the Chandra resolution (and thus cannotsubtract a constant background) This choice is motivatedby the desire to minimize artificial smoothing due to therelatively small scales of the ISM However we do applythe exposure correction across the medium as an adjustmentto the brightness of each pixel and we energy filter theimage based on the spectrum The radius of the (circular)aperture we use is straightforwardly determined from a one-dimensional radial profile extracted from annuli centeredon the AGN We excise the AGN emission through energyfiltering and masking a point-spread function (PSF) wecreated at the location of the AGN using the CIAO toolmkpsf We mask the region corresponding to the 95encircled energy ellipse One might worry that (especiallywith very bright AGN) this procedure would bias ourmeasured ε or PA but this appears not to be the casethe AGN is also usually centered on the nominal aim pointso εPSF is usually small The remaining counts within theaperture are fed into our ellipse-fitting routine Becausebackground is not subtracted the bootstrap method is likelymore accurate but our measured ε values are systematicallylow (though not very low thanks to the high contrast of thecompact ISM) We note that toggling pixel randomizationappears to have no effect on our results

2 Intragroupintracluster medium Because the IGM is typi-cally quite faint and extended we must bin the chip quitecoarsely to see the enhanced surface brightness We maskthe ISM and all other point sources then bin to 16 times16 pixels and apply a similarly binned exposure correc-tion Energy filtering is applied based on the spectrum Fi-nally we smooth the image with a Gaussian kernel (σ = 2coarsely binned pixels) We subtract background levels us-ing either empty regions on the chip (if the visible extentof the IGM is small) or blank sky files if the medium fillsthe chip The background files are similarly energy filteredand binnedsmoothed We choose circular apertures moti-vated by the idea that all our radio galaxies have escapedthe ISM but only some have escaped the ldquolocalrdquo IGM (Sec-tion 33) By ldquolocalrdquo IGM we specifically mean we use anaperture guided by the characteristic radius r0 determinedin one-dimensional radial profile fitting centered on the ra-dio galaxy Where r0 is not well constrained we take anaperture roughly bounding the ldquo2σrdquo isophote (where ldquo1σrdquois taken to be the background level in the binned smoothedimage) We then fit the IGM assuming it is a smooth ellip-soid on the scales of interest (ie no internal structure) sothe range in plate scale is not important between galaxiesA brief inspection of the isophotes indicates that this is agood first-order description on large scales but wrong nearthe center Inside our chosen aperture the bootstrap methodessentially tracks the contrast of structure against noise sothe uncertainty is also a function of the background level wesubtract Nonetheless the PAs are reasonably constrainedNotably there are a few cases where there is strong IGMICM not centered on the galaxy (NGC 326 and 3C 831B)but we ignore the emission that cannot be ldquoseenrdquo by theradio galaxy Additionally in B2 1040+31A the most sig-nificant IGM is a smaller structure centered on the radiogalaxyrsquos host system enveloped in a larger much dimmer


Table 5Ellipse Parameters for the ISM

Name εXminusray PAXminusray εXminusray PSF PAXminusray PSF εDSS PADSS εSDSS PASDSS PAjets PAwings

() () () () () ()

XRGs

B2 1040+31A 021 plusmn 007 158 plusmn 11 007 58 015 plusmn 002 153 plusmn 22 159 58NGC 326 0084 plusmn 0009 130 plusmn 37 009 134 0037 plusmn 0004 153 plusmn 33 120 423C 403 047 plusmn 003 35 plusmn 5 011 108 027 plusmn 009 39 plusmn 35 72 1334C +0058 015 plusmn 002 138 plusmn 17 007 161 051 plusmn 008 139 plusmn 6 044 plusmn 002 138 plusmn 3 65 143C 192 004 plusmn 001 126 plusmn 22 006 146 0018 plusmn 0005 119 plusmn 40 0018 plusmn 0002 132 plusmn 38 123 543C 433 009 plusmn 002 156 plusmn 40 004 172 03 plusmn 01 172 plusmn 21 169 84

Comparison sample

3C 449 014 plusmn 002 6 plusmn 15 016 30 021 plusmn 003 8 plusmn 6 93C 31 0087 plusmn 0003 112 plusmn 16 018 159 010 plusmn 001 142 plusmn 12 1603C 831B 017 plusmn 001 166 plusmn 16 012 1 019 plusmn 002 161 plusmn 17 963C 264 0042 plusmn 0002 129 plusmn 27 017 148 0044 plusmn 0003 129 plusmn 27 0011 plusmn 0005 160 plusmn 32 303C 66B 015 plusmn 001 128 plusmn 9 015 13 013 plusmn 001 131 plusmn 15 603C 296 015 plusmn 002 137 plusmn 6 017 147 019 plusmn 002 151 plusmn 13 023 plusmn 001 147 plusmn 6 35PKS 2153minus69 022 plusmn 003 106 plusmn 8 017 34 025 plusmn 004 126 plusmn 12 136NGC 6251 0047 plusmn 0002 25 plusmn 23 015 72 011 plusmn 001 24 plusmn 13 1153C 98 019 plusmn 004 92 plusmn 24 013 90 010 plusmn 003 62 plusmn 20 103C 465 0061 plusmn 0003 51 plusmn 29 017 74 017 plusmn 008 33 plusmn 25 1263C 293 030 plusmn 007 84 plusmn 18 005 110 050 plusmn 006 64 plusmn 7 029 plusmn 005 60 plusmn 10 1263C 285 021 plusmn 003 141 plusmn 18 019 96 036 plusmn 006 133 plusmn 13 036 plusmn 005 125 plusmn 9 733C 227 011 plusmn 001 19 plusmn 20 033 98 009 plusmn 002 27 plusmn 17 65

Notes Position angles (PAs) are reported counterclockwise from north (0) and chosen to reflect the acute angle between the major axes of the X-rayoptical and radio ellipses The error bars are reported at 95 using our ellipse-fitting method (Section 31) Radio PAs are estimated visually and havean estimated error of ΔPA sim 10 The PSF values are reported for the best-fit PSF used to mask the AGN emission

atmosphere with a different PA Using the methods abovewe take the smaller structure to be the local IGM

We treat the optical DSS data similarly We do not furtherbin the images and we measure the background near the hostgalaxy (but away from companions which we mask) We use anaperture corresponding to the extent of the hot ISM emissionWe wish to use similar apertures in the X-ray and opticalimages because ε may (physically) vary with r In the inneroptical isophotes both ε and PA may be (artificially) radiallydependent due to convolution with the PSF and viewing a triaxialobject (isophotal ldquotwistsrdquo) respectively (Binney amp Merrifield1998) Inner isophotes have dramatically lower values of ε thanthe outer ldquorealrdquo values (as in Tremblay et al 2007) The isophotaltwists on the other hand are a consequence of viewing a triaxialobject at a viewing angle not aligned with any of its axes Eitheris potentially a problem for our optical fitting when the X-rayISM aperture is small but usually the X-ray emission is extendedsufficiently that most of the optical light in our aperture comesfrom regions where dεdR is small isophotal twists are onlyseen in the very central regions of a few nearby galaxies inour DSS data None of our sources are quasars or appear to besaturated

32 OpticalndashX-ray Correlation

Because long (50ndash100 ks) exposures are often required tosee the diffuse X-ray gas even in nearby galaxies it is plainlyattractive to adopt the optical light as a proxy for the hot ISMTo zeroth order the stars and ISM should coincide but the ISMmay not be in hydrostatic equilibrium with the host (Diehl ampStatler 2007) and may be disturbed by recent mergers presumedto power the AGN In fact Diehl amp Statler (2007) find (in ananalysis of 54 Chandra detections of hot ISM) that the gasellipticity and morphology differ significantly from the starlight

Table 6Ellipse Parameters for the Local IGMICM

Name εIGM PAIGM PAjets PAwings

() () ()

XRGs

B2 1040+31A 018 plusmn 008 130 plusmn 30 159 58PKS 1422+26 013 plusmn 003 88 plusmn 14 92 179NGC 326 020 plusmn 004 128 plusmn 20 120 424C +0058a 015 plusmn 002 138 plusmn 17 65 143C 315 038 plusmn 006 23 plusmn 7 12 120

Comparison sample

3C 449 03 plusmn 01 41 plusmn 12 9

3C 31 018 plusmn 001 123 plusmn 4 160

3C 296 023 plusmn 004 121 plusmn 8 35

PKS 2153minus69 013 plusmn 003 140 plusmn 10 136

3C 338 0243 plusmn 0002 65 plusmn 6 90

3C 465 037 plusmn 002 53 plusmn 3 126

Cyg A 02 plusmn 01 22 plusmn 4 115

3C 445 03 plusmn 01 77 plusmn 8 169

3C 285 028 plusmn 006 163 plusmn 9 73

3C 452 043 plusmn 003 83 plusmn 2 78

3C 388 (l) 013 plusmn 002 65 plusmn 6 55

3C 388 (s) 0088 plusmn 0005 133 plusmn 18 55

Notes The error bars are reported at 95 using our ellipse-fitting methodbut are likely underestimates Images are processed before fits (Section 31) bybinning and smoothing due to the extended faint emission For 3C 388 we usethe large (l) ICM value but note the smaller ICM has a distinct position angle(Section 33)a The same values for 4C +0058 are used in the ISM ellipse table The identityof the medium we fit is ambiguous

although their sample only overlaps our own by a small amountAcknowledging that a detailed view of the inner ISM shows


Figure 4 Spectra of the X-ray IGM we use in our morphology comparison (Table 6) The XRG sample is shown with galaxy names in green and the total model fithas been plotted over the data in red The values can be found in Table 3


significant differences from the starlight we ask whether thestarlight is a sufficient proxy for the ISM in gross morphology(ie we are interested in the outer X-ray ldquoisophotesrdquo) orwhether it is of such different character that it weakens theCapetti et al (2002) and Saripalli amp Subrahmanyan (2009)analyses

In fact our work supports the identification of the opticallight as an appropriate proxy for the hot ISM However incontrast to C02 we do not find that XRGs are preferentially ingalaxies with higher ε although we note that our X-ray ε valuesare probably underestimated For the subset of our combinedsample with strong ISM emission (19 of 26 galaxies) we finda correlation coefficient of R = 060 (Figure 6) between theellipticity of the X-ray light (εX-ray) and the ellipticity of thehost galaxy in the DSS images (εDSS) The correlation between

the PAs of the best-fit ellipses is even stronger (R = 096) butthis is not meaningful because we expect a positive correlationeven if the ellipses are misaligned This is because an ellipsemay have a PA anywhere between 0 lt PA lt 180 butwhen considering the angular separation of the PAs of twosuperimposed ellipses one of the angles of separation mustbe acute Therefore a better measurement of the agreementbetween the optical and X-ray PAs is shown in Figure 6 wherethe distribution of ΔPA = PAISM minus PAoptical is shown Thevalues in Figure 6 are presented in Table 5 The uncertainties aregiven at the 2σ level from the bootstrap method For N = 21our results are significant at the 95 level The values weuse are given in Table 5 along with a comparison of DSS toSDSS values (and our ISM values to the best-fit AGN PSFvalues)


Figure 5 Spectra extracted from the central PSF of the host galaxy emission may come from either the parsec-scale jet or accretion disk region The total model fithas been plotted over the data in red and XRG galaxies have their names in green The spectra are essentially broken into absorbed and unabsorbed spectra some ofthe unabsorbed spectra require thermal components Note that 3C 338 has no detected AGN emission and 3C 403 has a small ISM represented in the spectrum of thearea near the AGN


We check our results for the optical values against theliterature where profile and isophotal fitting is standard Ourdistribution of optical ε peaks slightly below ε = 02 andfalls off quickly at higher values This is in agreement with theHST study by Martel et al (1999) but is slightly rounder than

the reported distributions in the ground-based studies of radiogalaxies by Smith amp Heckman (1989) and Lambas et al (1992)whose distributions peak at ε = 02 and 025 respectivelyThe small excess of very round hosts may be real (it persistseven when ε is measured at larger radii than reported) but our


Figure 6 Top Comparison of the eccentricities of the diffuse ISM to the opticallight where ε in each case has been generated by our ellipse-fitting method(Section 31) The dashed line represents a 11 correlation rather than a best-fitline Bottom Comparison of the PAs of the best-fit ellipses for the diffuse ISMto those of the optical light where the values are determined by our ellipse-fittingmethod (Section 31)


method may also underestimate ε The ε measurement has beenmade for far fewer sources in the X-ray band so a systematiccomparison is difficult In addition we compare our optical εand PA values for the XRG sample specifically to any matchingsources in the C02 and S09 studies (Table 4) and find generallygood agreement In other words in the X-ray band we (to someextent) reproduce the C02 and S09 results

Additionally we note here a few caveats First we do nottake into account the possible XRB contamination of the ISMWe do not consider this a significant problem based on ourspectroscopic analysismdasheven though low-mass X-ray binary(LMXB) spectra are often stronger at lower energies the thermalmodels are much better able to fit the peaks in the ISM spectraand are often sufficient for an adequate fit without requiringa power law This is consistent with Sun et al (2005) whodemonstrate that the XRB contribution to the emission is usually

less than 10 of the luminosity in many of our spectra welack the signal to distinguish a lt 10 contribution Second asnoted in Section 31 our X-ray ε values tend to be systematicallyunderestimated This makes a comparison with for example theDiehl amp Statler (2007) work difficult Notably there is one strongoutlier in 3C 403 whose εX-ray = 047 plusmn 003 is much higherthan its optical ellipticity Kraft et al (2005) find an even highervalue of εX-ray = 057 plusmn 004 using a profile fitting technique(they also compare εX-ray to HST εoptical) so it appears likelythat the 3C 403 ISM is indeed out of equilibrium Howeverthe case of 3C 403 is noteworthy in that the small extent ofthe ISM relative to the AGN emission makes energy filtering amore effective way to remove the AGN prior to fitting Kraftet al (2005) use a 03ndash10 keV window but it is difficult toconclude with certainty that this emission is ldquodominatedrdquo by thehot gas because it is possible to obtain a good fit to the spectrum(shown in Figure 5) using an unabsorbed power law between03 and 20 keV If 3C 403 is indeed badly out of equilibrium itappears to be an isolated case in our sample

33 X-rayndashRadio Correlation

We now measure the correlation between the PAs of theX-ray media and the radio jets by asking whether the quantityΔPA = |PAradio minus PAXminusray| is uniformly distributed for theXRGs and normal radio galaxies A uniform distribution meansthat for a given sample there is no preferred alignment betweenthe radio jets and the PA of the surrounding hot gas The radiojets are highly collimated and their orientation is determinedldquoby eyerdquo we believe the values are accurate to within 10The ellipticity and PA of the X-ray emission are determinedas described in Section 31 but to which medium shall wecompare the alignment of the jets Our goal is to determinewhether XRGs reside preferentially in media elongated alongthe jet axis In the overpressured cocoon model this medium isassumed to be the ISM but there are a few XRGs (NGC 326and PKS 1422+26) for which the ISM cannot be the ldquoconfiningrdquomedium because the wings are produced outside the ISMTherefore we must consider how to deal with the IGMICMWe describe the process of IGMICM aperture selection afterour ISM comparison In our discussion the ldquorelevantrdquo mediumis the one which could potentially confine the radio galaxy

1 Interstellar medium All of our radio galaxies have escapedthe ISM but it must have been the relevant medium for allof them at early stages Assuming that the jet orientationrelative to the ISM has not changed over the life of theradio galaxy it is straightforward to compare ΔPA for thenormal radio galaxies and the XRGs using the ISM In theC02 model we expect that the XRGs would have a smallangular separation between the ISM major axis and theradio jets ie ΔPA sim 0 Figure 7 bears this expectationout (values reported in Table 5) The aperture for the ISMwas the same as described in Section 32 and we exclude thesame five galaxies Figure 7 includes six XRGs and showsthe distributions of both the active and secondary lobes Asnoted in Section 32 the agreement between the gas andthe starlight is good Neither XRG distribution is consistentwith a uniform distribution (P = 004 for the primary lobesand 001 for the secondary lobes) despite the small samplesize whereas the normal radio galaxies are consistent withuniform distributions (P sim 10) The normal FR I ΔPAdistribution is only marginally consistent with uniform(although dramatically different from the XRGs) and may


be influenced by the giant radio galaxies which S09 notedtend to have jets aligned along the minor axis of the hostThis result is in our view strong evidence for the C02model although it was anticipated from Section 32 TheIGM may be the confining medium for several XRGs butthe strong agreement with the C02 geometry in the ISMsuggests that the ISMndashjet orientation may be intrinsicallyimportant The overpressured cocoon model put forth toexplain this geometry should not be confused with theobserved result

2 Intragroupintracluster medium Because the XRGs existwhose wings could not have been produced by the ISMin the C02 model we want to see if the C02 geometryexists among IGM atmospheres as well We thus have toconsider how to choose apertures in the IGMICM for thecomparison sample as well There is no obvious way tocompare these media for various radio galaxies especiallysince some of our control sample radio sources extend farbeyond the chip boundaries

However using the same logic as above we can measurethe elongation and orientation of the ldquolocalrdquo IGMICM(Section 31) All sources larger than the local IGMICMmust have passed through it at one point and it is therelevant medium for all sources enclosed by it and outsidethe ISM As mentioned in Section 31 we assume that theIGMICM is described by a smooth ellipsoid so the PAsare comparable between sources of vastly different scale(the gradients are more important) We therefore expectthe ΔPA values to be uniformly distributed in the controlsample

We detect IGMICM emission in fewer galaxies but weinclude the five galaxies with IGMICM but no clearlydistinguishable ISM (3C 338 3C 388 3C 445 3C 452and Cyg A) We thus have five normal FR I galaxies sevennormal FR II galaxies and five XRGs Of the XRGs theIGMICM is the relevant medium for NGC 326 and PKS1422+26 and may be the relevant medium in 3C 315 4C+0058 and B2 1040+31A Although the sample sizes aresmaller the ΔPA distributions for the FR I and II galaxiesare consistent with uniform (P = 03 and 04 respectivelyFigure 8) The XRG sample on the other hand is notconsistent with a uniform distribution (P = 002 for boththe primary and secondary lobes) Our values are found inTable 6

In 3C 452 the X-ray emission traces the radio emission sowell that the geometry of the extended emission probablyrepresents the radio galaxy cocoon or a bounding shockand not the actual IGM (even when a purely ldquothermalrdquoimage is reconstructed Appendix A1) Similarly the radiolobes of 3C 388 may be responsible for the geometry ofthe surrounding medium and the inner isophotes of thesurrounding ICM are elongated perpendicular to the jet Ifwe exclude 3C 452 and use a smaller aperture in 3C 388 asthe ldquolocalrdquo ICM our results for the IGMICM comparisonoutlined above are unchanged (the normal FR II galaxiesstill look uniformly distributed)

We cannot easily compare a mix of ISM and IGMICMrelevant media in the XRG sample to the comparison sampleHowever we can do this for the XRG sample because wehave the additional spatial information of the secondary lobesWhen we use the IGM values for NGC 326 and PKS 1422+26the distribution of ΔPA obeys the C02 correlation even morestrongly than for the ISM or IGM alone The probability that

Figure 7 Comparison of the alignment of the radio jets with the interstellarmedium (filled) and the optical light (hashed) ΔPA is the acute angle betweenthe major axes of the best-fit ellipses (Section 31) and the orientation of theradio jets ΔPA sim 0 indicates alignment of the major axis of the medium withthe radio lobes whereas ΔPA sim 90 indicates alignment with the minor axisNote not all galaxies are represented here

the ΔPA distribution for this ldquobest guessrdquo sample is drawnfrom a uniform parent is P = 0006 for the primary lobes andP = 0001 for the secondary ones Regardless the samplesindividually are distinguishable from normal radio galaxies bytheir jetmdashmedium geometry

Does this geometry necessarily implicate the overpressuredcocoon model NGC 326 3C 433 and 4C +0058 obey the C02geometry but would be difficult to form in the overpressuredcocoon model alone NGC 326 for example is a well studiedXRG which has longer secondary lobes than primary ones Thisposes a problem for the overpressured cocoon model since weexpect the jets to expand supersonically and the wings to be (atmost) transonic The long secondary lobes may therefore implybuoyant evolution of the backflow (Worrall et al 1995) althoughsubsonic expansion of the primary lobes is possible 3C 433 isan especially odd case since the southern radio lobes are ofqualitatively different character than the northern counterpartsMiller amp Brandt (2009) argue that the difference between thenorthern (FR I) and southern (FR II) lobes is due to propagatinginto a very asymmetric medium The secondary lobes are closeto the ISM so it is ambiguous which medium is relevant forXRG formation Lastly 4C +0058 appears to violate the C02geometry as the jet appears to come out of the minor axis ofthe ISM 4C +0058 almost certainly disagrees with the C02geometry in the optical image (due to the high ε the major axisis likely to be close to the plane of the sky) and we detect anX-ray jet cospatial with the northern radio jet However it is


Figure 8 Comparison of the alignment of the radio jets with the local IGM(filled see the text) and the optical light (hashed) ΔPA is the acute anglebetween the major axes of the best-fit ellipses (Section 31) and the orientationof the radio jets ΔPA sim 0 indicates alignment of the major axis of the mediumwith the radio lobes whereas ΔPA sim 90 indicates alignment with the minoraxis Not all galaxies are represented here

unclear that the extended X-ray emission comes entirely fromthe ISM Deeper follow-up observations are required to assessthe role of the IGM in this source and establish whether it isactually a counterexample to the C02 geometry 3C 192 is anambiguous case because although it obeys the C02 geometry theeccentricity of the ISM is small For 3C 192 to be produced inthe overpressured cocoon model small differences in pressuregradients must be important

4 PROPERTIES OF THE CENTRAL ENGINE

In the backflow models FR II morphology is thought to benecessary to drive strong backflows Although the backflowsbegin at the hot spots edge-brightened FR II morphology isstrongly associated with absorbed power-law AGN emissionWe note that several galaxies in our XRG sample are notunambiguously FR type II (some of the galaxies with poordata are FR I) so we attempt to characterize the XRG sample interms of absorbed or unabsorbed AGN spectra Highly absorbedspectra tend to have higher LX for a given flux than unabsorbedspectra owing to the large amount of ldquoabsorptionrdquo blockingthe low-energy photons whereas unabsorbed spectra tend to belower energy with small X-ray luminosities above sim2 keV

Our model fitting of the AGN spectra started by fitting asingle power law (either absorbed or unabsorbed depending onthe appearance of the spectrum) Additional complexity wasadded as the degrees of freedom allowed until an acceptable

Figure 9 Distribution of the XRG and comparison sample model luminositiesfor spectra extracted from the central PSF The luminosities are calculatedfor the full model fit FR II galaxies tend to have highly absorbed spectra withcorresponding high luminosities whereas FR I galaxies tend to have unabsorbedspectra XRGs have both absorbed and unabsorbed spectra

fit was achieved We note that NH and Γ are often degenerateand require one of the two to be frozen (to values ranging fromΓ = 10ndash20 Table 7) All the fits also incorporated GalacticNH Our model parameters and luminosities are given in Table 7and are largely in accordance with previous studies of the 3CRRChandra sample (Evans et al 2006 Balmaverde et al 2006)These papers have also conducted a more exhaustive study ofthe AGN X-ray emission whereas our purpose is to determinewhether this emission lends insight to the XRG sample

In fact the XRG sample cannot neatly be classified in terms ofabsorbed or unabsorbed spectra (Figure 9) This is in agreementwith other evidence (eg optical data from Cheung et al 2009)although the highly absorbed XRGs do not tend to have a smallerLX than the normal FR II galaxies Indeed the XRG samplewhile small is consistent with the distribution of LX between1040 and 1044 erg sminus1 for the full comparison sample and notwith either the normal FR I or II galaxies by themselves Wenote that we detect X-ray jets in some of our systems but wefind no evidence for misaligned jets in any of the XRGs Thesample size is too small to rule out the Lal amp Rao (2007) modelon this basis but we might expect to see misaligned jets in theirscheme

5 DISCUSSION AND SUMMARY

We present new and archival Chandra data of XRGs alongsidenormal FR I and II galaxies within z 01 We extend theCapetti et al (2002) and Saripalli amp Subrahmanyan (2009)geometric correlation between the orientation of the secondarylobes in XRGs and the minor axis of the interacting mediumto the X-ray band including the IGMICM We find that thisgeometry strongly distinguishes the XRGs from normal radiogalaxies (although we are unable to strongly distinguish betweenXRGs and normal radio galaxies using only the local IGMICMvalues) and that XRGs may be produced in galaxies with bothabsorbed and unabsorbed AGN Our results in the X-ray bandare consistent with Cheung et al (2009) who find that XRGs lieclose to the FR III division in a comparison of radiondashopticalluminosity We note that in properties of the hot atmospheres(temperature density and pressure) the XRG sample appears


Table 7Radio Galaxy Nuclei X-ray Spectral Parameters

Galaxy z Galactic NH Models Local NH Γ kT Luminosity χ2dof(1020 cmminus2) (1022 cmminus2) (keV) (1042 erg sminus1)

XRGs

PKS 1422+26 0037 154 NH(PL+Gauss) 4 plusmn 1 05 plusmn 04 38 8216NGC 326 0048 586 NH(PL)+apec 05 (f) 13 plusmn 04 068 plusmn 006 015 111163C 403 0059 122 NH(PL+Gauss)+PL+apec 46plusmn 5 Γ1 = 19 plusmn 01 024 plusmn 003 166 100794

Γ2 = 20 (f)4C +0058 0059 714 PL 13 plusmn 06 11 1643C 192 0060 408 NH(PL) 16 (f) 20 (f) 31 0923C 433 0102 777 NH(PL+Gauss)+apec 8 plusmn 1 11 plusmn 01 10 plusmn 02 59 72577

Comparison sample

3C 449 0017 899 NH(PL)+apec 05 (f) 16 plusmn 02 059 plusmn 008 005 76143C 31 0017 536 PL+apec 19 plusmn 01 070 plusmn 003 013 81833C 831B 0018 134 NH(PL)+apec 22 plusmn 09 20 plusmn 03 048 plusmn 008 005 227363C 264 0021 183 PL+apec 213 plusmn 003 034 plusmn 006 17 15271543C 66B 0022 767 PL+apec 217 plusmn 006 052 plusmn 008 033 9061143C 296 0026 192 NH(PL)+apec 010 (f) 11 plusmn 01 068 plusmn 002 038 91881NGC 6251 0024 559 NH(PL)+apec 005 plusmn 001 15 plusmn 003 035 plusmn 005 80 391386PKS 2153minus69 0028 267 pileup(PL)+apec 149 plusmn 005 04 plusmn 02 122 731863C 98 0030 108 NH(PL)+gauss+PL 9 plusmn 1 Γ1 = 12 (f) 31 47435

Γ2 = 15 (f)3C 465 0031 482 NH(PL)+apec 03 (f) 24 plusmn 02 083 plusmn 006 031 620623C 293 0045 127 NH(PL)+apec 11 plusmn 4 15 (f) 155 (f) 45 9310Cyg A 0056 302 pileup(NH(PL))+gauss+cflow 25 plusmn 2 20 (f) 876 29432173C 445 0056 451 pileup(NH(PL))+gaussa 16 plusmn 1 17 (f) 47 624443C 285 0079 127 NH(PL)+gauss 28 plusmn 4 12 (f) 87 12693C 452 0081 964 NH(PL)+gauss+apec+PEXRAVb 38 plusmn 9 165 (f) 08 plusmn 02 25 15661453C 227 0087 211 pileup(NH(PL))+PL 33 plusmn 01 Γ1 = 175 (f) 155 2489167

Γ2 = 10 plusmn 023C 388 0091 558 PL+apec 23 plusmn 03 12 plusmn 02 19 14116

Notes Reported errors for Γ are the smaller of the values given by 90 confidence intervals determined in XSPEC if there is significant asymmetryabout the best-fit value the larger error bar is ill defined (f) denotes a frozen parameter and complex model components are discussed in theAppendixwith the relevant galaxy The ldquofitsrdquo to low-count spectra (eg 3C 192 or 4C +0058) are not reliable but they do constrain well whether the spectrumis absorbed or unabsorbed so we report them only for an order-of-magnitude luminosity estimatea Complex emission between 05 and 30 keV is ignored see the Appendixb PEXRAV is a reflection model from Magdziarz amp Zdziarski (1995)

indistinguishable from the comparison sample (Table 3) but thatthese parameters are spatial averages of profiles and may not bedirectly comparable

The remarkable geometric distinction between the normaland XRGs may be an important clue to the genesis of thesecondary lobes We cannot rigorously examine the forma-tion models in our data but identify potential problems forthe backflow models in several galaxies The backflow schemesnaturally explain the observed geometry but also have yet toexplain other features of XRGs in detailed modeling (eg theflat spectral indices of the secondary lobes Lal amp Rao 2007)However the models are presently immature the C02 over-pressured cocoon model has only been modeled in a highlyelliptical two-dimensional ISM whereas the Kraft et al (2005)suggestion that the buoyant backflow mechanism can produceX-shaped wings in the presence of an anisotropic buoyantmedium has not been modeled Three-dimensional modelingand deeper observations of the relevant media in XRGs are re-quired to make a convincing case for either of these models No-tably the rapid reorientation models have yet to present a reasonfor the C02 correlation Any successful model must account forit Lastly deeper observations of the XRGs in our sample forwhich no diffuse emission was detected are required The to-tal sample of nearby XRGs is quite small so every member isimportant

CSR and EH-K thank the support of the Chandra GuestObserver program under grant GO89109X EH-K thanks A IHarris for useful discussion of the ellipse-fitting method CCCwas supported by an appointment to the NASA PostdoctoralProgram at Goddard Space Flight Center administered by OakRidge Associated Universities through a contract with NASAThis research has made use of the NASAIPAC ExtragalacticDatabase (NED) which is operated by the Jet PropulsionLaboratory California Institute of Technology under contractwith the National Aeronautics and Space Administration TheDigitized Sky Surveys were produced at the Space TelescopeScience Institute under US Government grant NAG W-2166The images of these surveys are based on photographic dataobtained using the Oschin Schmidt Telescope on PalomarMountain and the UK Schmidt Telescope The plates wereprocessed into the present compressed digital form with thepermission of these institutions

Facilities CXO VLA

APPENDIX

NOTES ON INDIVIDUAL GALAXIES

A1 XRGs

B2 1040+31A (z = 0036) The radio galaxy emanates fromthe largest galaxy in a close triple system (Fanti et al 1977)


which itself is contained within a large region of IGM Thelarger IGM is in agreement with Worrall amp Birkinshaw (2000)but for the relevant medium we use a smaller region of IGMwhich is bright against the large region and centered on thesystem In the DSS image the host galaxy cannot be isolatedfrom its companions so we use the SDSS image alone In theX-ray band the host galaxy is bright whether it is AGN emissionis unclear based on the spectrum Because the character of theemission does not change much outside the PSF we assume weare seeing primarily thermal emission

PKS 1422+26 (z = 0037) This galaxy has striking wingsand ldquowarmrdquo spots which occur about 50 of the distancebetween the lobe edge and the radio core The radio galaxy defieseasy FR classification and is here considered a hybrid FR IIIgalaxy Canosa et al (1999) found radial asymmetry in theROSAT image of the IGM which the Chandra image confirmsThe radio hot spots coincide well with decrements in the X-rayimage which must be cavities blown in the gas by the radio lobesThe surface brightness of the ldquoridgerdquo this leaves in the middleis consistent with the hypothesis that the actual orientation ofthe IGM is elongated in the direction of the radio lobes Thisis in contrast to 3C 285 or 3C 388 where cavities alone cannotexplain the ldquoexcessrdquo emission near the core In addition thespectrum of the AGN has a highly significant emission line-likefeature at 40 keV which is presently unexplained

NGC 326 (z = 0048) NGC 326 is a double galaxy withthe radio lobes emanating from the northern component bothgalaxies show diffuse X-ray ISM emission and the X-rayemission from the southern galaxy is exclusively thermal Theextent of the Chandra diffuse emission agrees well with theROSAT data where there is overlap (Worrall et al 1995) Thelong tails in the radio map appear to follow empty channelsin the Chandra data and the length of the tails relative tothe active lobes provides constraints on backflow formationmechanisms (Gopal-Krishna et al 2003) The ISM emissionfor the northern component is extracted excluding the centralpoint source the temperature of kT = 068 keV agrees preciselywith the temperature of the thermal model included in the AGNemission where a PL component is also required

3C 403 (z = 0059) This data set was previously studiedin detail by Kraft et al (2005) who attempted to isolatethe ISM emission from the nucleus by performing a spectralanalysis in which the soft part of the spectrum was fitted byan absorbed power law between 10 and 20 keV with a line-dominated thermal fit between 03 and 10 keV They then fit anelliptical profile to these thermal events This line of reasoningis supported by the absence of a bright core corresponding to thePSF at 03ndash10 keV However we find an acceptable fit in whichan unabsorbed power law dominates between 03 and 20 keVThis analysis is also complicated by the presence of a featureat 085 keV which is not fit by either Kraft et al (2005) orourselves Since this feature accounts for sim25 of countsbetween 03 and 10 keV (Figure 5 we cannot distinguishbetween the thermal and power-law models) It should be notedthat the PA of the soft emission agrees well with the hostgalaxy we are doubtless seeing some ISM However we do notknow if it is the dominant component

4C +0058 (z = 0059) 4C +0058 was classified as acandidate XRG (Cheung 2007) due to faint wings in the FIRSTimage A new higher resolution radio map reveals that the jetto the east of the core is bent toward the northwest and enclosedin a more symmetric radio lobe We detect the inner part of thisjet in the X-ray band (confirmed by line-fitting to determine the

PA using the bootstrap resampling method) The PA of thejet was determined very well so we masked it from our fit Itis unclear whether the diffuse emission represents the ISM orthe IGM εX-ray does not agree well with the host galaxy butthe PA does There is likely some of both media represented inthe image and deeper observations are required to separate thecomponents Notably the jet appears to pass through the minoraxis of the host galaxy We include this galaxy in both the ISMand IGM X-rayndashradio comparisons due to the ambiguity

3C 192 (z = 0060) 3C 192 is formally a ldquowingedrdquogalaxy (Cheung 2007) but the morphology is otherwise verysimilar to XRGs Enhanced emission is detected in an ellipticalregion encompassing the primary radio lobes but a smallerenhancement we identify with the ISM exists near the AGNIt is also possible that this is the central region of the IGMbut it appears compact Moreover the ldquoIGMrdquo is consistent withbeing fit only by a power law (Γ = 25) and is in good spatialagreement with the primary lobes It may also be fitted by athermal model with kT sim 09 and Z lt 01 if it is indeedthermal emission the IGM is in perfect agreement with Capettiet al (2002) However a close inspection of the radio galaxysuggests that the X-ray emission may come from a boundingshock or otherwise have been influenced by the radio galaxyrather than a pre-existing highly eccentric IGM In particulareven though the bright X-ray emission is not as large as theactive lobes the southwestern lobe appears to track enhancedX-ray emission to its hot spot Notably 3C 192 is in a very roundhost (Smith amp Heckman 1989 Cheung amp Springmann 2007)Capetti et al (2002) found XRGs typically occur in galaxieswith high projected ε so the existence of similar morphologyin round hosts bears investigation

3C 433 (z = 0102) The northern secondary lobe of 3C 433is strikingly bent compared to the southern secondary (vanBreugel et al 1983) Miller amp Brandt (2009) argue that thehybrid FR III lobe morphology is due to interaction with thesurrounding IGM In this scenario the galaxy is a typical FR IIsource propagating into a very asymmetric environment Milleramp Brandt (2009) also include in their paper a HST image of thehost galaxy whose PA is in good agreement with the parameterswe derive from the DSS image The X-ray emission near thesouthern lobe is consistent with either thermal emission (Milleramp Brandt 2009) or power-law emission We assume the ISM isthe relevant medium and attempt to isolate it but we may alsobe incorporating some local IGM emission in the spectrum

3C 315 (z = 0108) The AGN is detected at a significanceof 507σ (see Appendix A3 for methods) but there are too fewcounts to make a spectrum The diffuse IGM stands out againstthe background on large scales and is fitted well by thermalmodels and not by power-law models No ISM is detected butwe can use the galaxy for comparison to the IGM independentlyIt is possible that this is not real IGM as we suspect in 3C 192but the alignment of the radio galaxy and the hot atmosphere isnot as good as in 3C 192 nor is it quite as eccentric Thus thereis no strong evidence that the radio galaxy created the observedX-ray morphology but the exposure is very short

A2 Comparison Sample

3C 449 (z = 0017) Both the ISM and IGM are bright in this30 ks exposure but the chip is somewhat smaller than the extentof the radio lobes Notably these lobes decollimate and showthe characteristic FR I plumed structure near the edge of theIGM this structure and the hot atmospheres have been studied


with XMM-Newton in detail by Croston et al (2003) Tremblayet al (2007) find that the jet is parallel to a warped nuclear diskThe AGN was fitted with the XSPEC models NH(PL)+apecbut the an acceptable fit was also found for a PL+apec fit withno absorption and a smaller Γ

3C 31 (z = 0017) The X-ray jet (Hardcastle et al 2002) isquite bright in the ACIS-S3 image and is readily distinguishablefrom other core X-ray emission so we mask it in the analysisof the diffuse ISM A weaker nearby source to the southwest(visible in the optical light) may contaminate the ISM with asmall amount of diffuse emission but appears very weak in theX-ray

3C 831B (z = 0018) The Chandra data from this headndashtailgalaxy was published by Sun et al (2005) who argue that there isa distinct southern edge to the X-ray emission which otherwiseshares the ellipticity and PA of the optical isophotes Theyapply a deprojection analysis to the ISM data and find that thecentral ISM has a temperature of kT = 045 keV in agreementwith our non-deprojected fit to the central PSF emission withkT = 048 keV Sun et al (2005) also find that the LMXBcontribution to the diffuse gas is on the order of sim5 and theyshow that the southern edge in the X-ray data cannot be producedby ICM pressure but argue that the edge is a sign of ISMICMinteraction and that if the galaxy is moving south very rapidlythe long twin tails to the north are naturally explained The radioemission is likewise curtailed to the south

3C 264 (z = 0021) 3C 264 is a headndashtail galaxy whose radiolobes both extend to the northeast but there is a large envelope ofradio emission around the AGN which is larger than the extentof the 2σsky DSS optical isophotes This data set is subarrayedto 18 of the ACIS-S3 area and suffers from a readout streakWe subtracted the streak and this removed a relatively smallnumber of photons from the diffuse ISM Both the host galaxyand the diffuse X-ray emission appear almost circular on thesky such that the PA of the ellipses we fit (Table 5) are not wellconstrained

3C 66B (z = 0022) We detect strong ISM emission andthe X-ray jet in this Chandra exposure The IGM is detectedand studied (with regards to its interaction with the radiolobes) using XMM-Newton data by Croston et al (2003) Inthe Chandra exposure however the IGM is very weak and wecannot measure the morphology The different character of thetwo lobes is attributed to interaction with the hot gas by Crostonet al (2003) with the western lobe being more confined Thereis a small unresolved source to the southeast in the X-ray imagewhich has an optical counterpart but it is far enough from theISM emission that our ellipse fitting is unaffected

3C 296 (z = 0024) Before fitting an ellipse we subtracta small companion to the northwest as well as the X-ray jetThe ISM is clearly detected (see also Diehl amp Statler 2007NGC 5532 in their paper) and the lobes begin expanding outsidethe IGM The IGM has a similar shape and orientation to theISM but it is clearly distinct in temperature and where it iscentered (in between 3C 296 and a companion to the southwest)even though it is relatively compact

NGC 6251 (z = 0024) The very large (Mpc-scale) radiolobes of this radio galaxy dwarf the entire ACIS array and the18 size S3 subarray contains emission only from the centralcore and along the jet (Evans et al 2005) We detect someemission associated with the jet to the northwest of the galaxyalong the chip A bright readout streak has been removed and wecorrect the spectrum of the central PSF for pileup The spectrumof the AGN is fitted well by either a power law with Γ lt 05 and

a thermal model or a slightly absorbed power law with Γ = 15and a thermal model

PKS 2153minus69 (z = 0028) This data have been publishedbefore with regard to interaction of the radio jet with a cloud ofgas (Ly et al 2005 Young et al 2005) The gross morphologyagrees well with the C02 geometric relation although the surfacebrightness decrement to the north and south of the galaxy is dueto the cavities blown out by the radio lobes as is evident fromthe visible shocked bubbles of gas in the IGM Despite thesecavities the morphology of the larger IGM is easily measurableon larger scales assuming the internal structure is entirely dueto the radio galaxy activity

3C 338 (z = 0030) Unlike other extended sources for whichdeprojection is possible but which can be fitted by an isothermalmodel to find an average temperature (most of the other galaxiesin our sample) 3C 338 has sufficient signal to require at least a2-T model to find average temperatures (signifying the presenceof hotter and cooler gas) and these temperatures are roughly inline with the outer and inner temperatures of the Johnstone et al(2002) deprojection analysis which also agrees with our own (wereport the 2-T fit for consistency) Although the cluster gas isinteracting with the radio galaxy it is otherwise smooth and wetake it to be a single large ellipsoid for the purpose of measuringellipticity and PA of the ICM Notably we do not detect theAGN or the ISM amidst the very bright ICM This observationis studied more thoroughly in Johnstone et al (2002) includingthe unusual radio bridge parallel to the jets

3C 98 (z = 0030) The ISM of the galaxy in this ACIS-Iobservation is very close to the chip boundaries However it hasclear ellipticity and is not contaminated by any companions sowe are able to fit an ellipse There is diffuse thermal emissionassociated with the northern radio lobe that is similar to theISM but we see no evidence for such gas in the southern lobeNotably the orientation of the major axis of the HST image inMartel et al (1999) disagrees with our DSS ellipse by sim20The HST image is more reliable meaning that the radio jet isaligned close to the major axis of the host

3C 465 (z = 0031) 3C 465 is a wide-angle tail FR I radiogalaxy located in cluster gas that has been well studied (bothwith Chandra and XMM-Newton by Hardcastle et al 2005)The ICM covers most of the chip and is centered on the host of3C 465 The ICM has clear ellipticity and the bright extendedemission is comparable to the size of entire radio galaxy Wefit ellipses to both the ISM and ldquolocalrdquo ICM on a scale slightlysmaller than half the size of the chip Hardcastle et al (2005)also present a radial profile which is in agreement with ouraverage temperature for the cluster gas The spectrum of theAGN can be fitted well either by a power law with Γ lt 05 anda thermal model or a slightly absorbed power law with Γ = 24and a thermal model

3C 293 (z = 0045) The X-ray emission associated with theradio galaxy is quite weak but the hot spots are distinct and thereis a small amount of extended ISM emission Unfortunately thespatial extent of this diffuse emission is small compared tothe optical isophotes so the disagreement between the εX-rayand εDSSSDSS (measured at a somewhat larger radius) is notespecially surprising Notably the host galaxy has two nucleiand is in the process of merging (Martel et al 1999)

Cyg A (z = 0056) Cygnus A has been extensively studiedin the X-rays thanks to its exceptionally bright filamentarystructure and evident shock cocoon tracing the radio galaxy Thisstructure makes it impossible to measure the ellipse parametersof the ISM but the larger ICM appears to have little structure


beyond the cocoon and filaments (Young et al 2002 show thatthe host galaxy has complex morphology as well) Thereforewe believe the directions of pressure and density gradients onlarge scales are likely to be similar to the ones the radio galaxyencounters

3C 445 (z = 0056) The bright nucleus of 3C 445 is far off-axis in this exposure its brightness and high ellipticity makeit impossible to measure the ellipse parameters of the diffuseISM Moreover the Martel et al (1999) HST image is dominatedby the unresolved nucleus so our DSS parameters may not beaccurate However we include the galaxy in our sample becauseof the hot IGM surrounding the host

3C 285 (z = 0079) 3C 285 is currently experiencing a majormerger and instead of a well defined ISM we fit an ellipse tothe ldquoridgerdquo structure described in Hardcastle et al (2007b) Theridge appears to be a unified structure (its X-ray properties donot differ along its length) and Hardcastle et al (2007b) arguethat it is not produced by the interaction of the radio galaxywith its environment They reason that the agreement with thestarlight (and in 3C 442A the flow of material from tidal tailsinto a similar ridge) could not be generally predicted by theinteraction of the radio galaxy with its environment This is inagreement with our ISMndashoptical light correlation

3C 452 (z = 0081) This data set was studied in detail byIsobe et al (2002) who find that the thermal and power-lawemission is well mixed throughout the region covered by theradio lobes We attempt to isolate the two components usingan analysis similar to Diehl amp Statler (2007) in which theimage is broken into hard and soft components The thermaland power-law emission each make up a certain percentage ofthe luminosity in each component so a synthesized image ofthe thermal emission can be constructed by adding the correctpercentage of each component to the final image Althoughclearly the method will not be able to identify individual countsas thermal or nonthermal in origin if the spatial distribution ofnonthermal counts is significantly different from that of thermalones we would expect to see a difference in the synthesizedimages In fact we find general agreement with Isobe et al(2002) although the nonthermal emission is dominant near thehot spots of the radio galaxy If the thermal X-ray emission tracesthe physical boundaries of the IGM then we would expect tosee either an X- or Z-shaped galaxy but the extremely goodcoincidence between X-ray and radio emission argues that thisis instead a cocoon inside a larger (unseen) IGM

3C 227 (z = 0087) 3C 227 exhibits both core ISMand dimmer IGM emission near the host galaxy The IGMmorphology is difficult to study due to the chip boundary Theradio lobes appear to be ragged and bend around the major axisof the host galaxy suggesting that strong backflows similar tothose in the hydrodynamic XRG formation models are at workbut the IGM is too weak near these mini-wings to assess thishypothesis The galaxy was included in the Hardcastle et al(2007a) study of particle acceleration in hot spots

3C 388 (z = 0091) 3C 388 is a radio galaxy oriented alongthe major axis of its host but we detect no ISM in the X-ray exposure due to the strength of the surrounding ICM Theradio galaxy is comparable to the size of X-ray ICM isophoteselongated in its direction which Kraft et al (2006) attribute tothe influence of the radio galaxy on its surroundings The radiolobes have blown cavities in the X-ray emission but near thecore of the radio galaxy the X-ray isophotes are elongated ina direction perpendicular to the radio lobes Although much ofthis asymmetry is likely due to the cavities eating out the sides of

a spheroid where the radio galaxy overlaps the core region (ieit is a physical structure but may not precede the radio galaxy)the western radio lobe seems to bend around the ridge Since thefainter portions of the radio lobes may be older plasma evolvingbuoyantly in the ICM (the jet in the western lobe is farther tothe south) the ridge may also be influencing the shape of theradio galaxy

A3 Unused XRGs

Short observations of the more distant XRGs producedmixed results with a number of sources exhibiting little-to-no diffuse emission Where we cannot determine whether anydiffuse emission is dominated by thermal emission or measuremorphology or where no diffuse emission corresponding tothe relevant medium is detected we cannot use the galaxy inour analysis In the following short observations the centralpoint source is detected in all cases (with the weakest detectionhaving a significance barely exceeding 3σ ) and upper limits aregiven for the thermal luminosity We use the methods of Ayres(2004 Equations (3) (13) and (14) in his paper) to measure thedetection significance and flux confidence limits The measurednumber of counts is given by

S = S0 +

(s2 + 2

3

)plusmn ΔS

where S0 = N minus B is the detected number of counts in the cellB is the expected background in the cell based on a much largerarea elsewhere on the chip and s is the significance we chooses = 1645 for 95 confidence intervals The quantity ΔS isgiven by

ΔS equiv s

radicmax[(N minus 1

4B) 0] + 1

The detect cells we used were uniformly chosen to be circleswith 3primeprime in radius to enclose the Chandra PSF at most energiesThe significance of the detection s was determined by solvingthe quadratic equation (Equation (3) in Ayres 2004)

min[B01 1]

7s2 +

radicBs +

[B minus N minus 2 middot min[B01 1]

7

]= 0

These values are reported for each galaxy The thermal lumi-nosity upper limits were computed by extracting a spectrumfrom a (large) region around the point source and increasing thestrength of a thermal model in XSPEC until it was no longer agood fit The temperature cannot be constrained and was thusfixed at kT = 10 keV The unabsorbed luminosity was thencomputed at the upper bound of the model normalization andreported below

4C + 3225 (z = 0053) The point source is detected witha significance of 852σ with S = 207+94

minus63 counts in the detectcell The diffuse emission within a r = 24primeprime region (much largerthan the ISM) has an upper limit unabsorbed thermal luminosityof 4 times 1040 erg sminus1 at sim10 keV but it does not appear to becentrally concentrated on the chip Our geometric analysis isnot possible in this case especially since the ISM is the mediumof interest given the scale of the radio emission

4C + 4829 (z = 0052) We detect 19 counts in the detectcell (positioned around the core of radio emission) and detectthe AGN with a significance of 756σ and S = 176+89

minus57counts in a 95 confidence interval The diffuse emission ina r = 24primeprime region is barely distinguishable from the background


and we measure an unabsorbed thermal luminosity upper limitof L = 5 times 1040 erg sminus1 We attribute this to the faint IGMas opposed to the ISM due to the scale and lack of centralconcentration

3C 1361 (z = 0064) This source has relatively highbackground so we detect the AGN at a significance of only33σ despite finding 11 counts in the detect cell The number ofcounts is S = 79+71

minus39 Any diffuse emission is similarly buriedin the background and we measure an unabsorbed thermalluminosity upper limit of L = 2times1040 erg sminus1 for a region withr = 30primeprime

J1101+1640 (z = 0068) Unfortunately this XRG was notpositioned on any ACIS chip during the observation The galaxylies in a cluster (Abell 1145) and the radio lobes just extendonto part of the S3 chip but no significant diffuse gas from thecluster is detected on the chip The observation was mispointeddue to an error in the primary literature and so cannot beused

3C 2231 (z = 0107) 3C 2231 actually has a bright AGNcore where spectroscopy is possible revealing a highly absorbedpower law The detection significance is 341σ and the numberof counts detected S = 206+25

minus22 However any diffuse emissionis extremely faint with an upper limit to unabsorbed thermalluminosity of L = 8 times 1040 erg sminus1 in a region with r = 30primeprimeWe are therefore unable to use this galaxy in our XRG sample

We also choose not to use the two Chandra observations ofXRGs at higher redshift (z = 0128 02854) because of therequirement to simultaneously expand the comparison sample(and 3C 1971 is not included in the compilation of Cheung2007) We address these here as follows

3C 1971 (z = 0128) 3C 1971 has a long northernwing which is comparable in spatial extent to the activelobe in a 15 GHz image (Neff et al 1995) but there is noobvious southern wing which could be described as symmetricabout the central AGN In the 5 GHz image of Neff et al(1995) extensions in the southern lobe appear to be essentiallysymmetric about the jet axis 3C 1971 is included in the Saripalliamp Subrahmanyan (2009) list of XRGs but its inclusion in oursample is questionable We discuss it here because of the otherldquoXRGsrdquo listed in Saripalli amp Subrahmanyan (2009) and notin Cheung (2007) 3C 1971 bears the most similarity to theclassical XRGs listed in Cheung (2007) We do not include itin our sample due to its relatively high redshift and ambiguityof classification The Chandra exposure is a short 8 ks snapshotwhich clearly detects the AGN and some diffuse emission whichmay be the ISM or the IGM but has insufficient counts to claima spectroscopic detection of hot gas

3C 52 (z = 0285) 3C 52 is a classical XRG with highlycollimated secondary lobes in the 15 GHz image (Alexanderamp Leahy 1987) and excluded from our sample on the basisof much higher redshift than our other sources The Chandraimage is an 8 ks snapshot which clearly detects the centralpoint source and also a diffuse atmosphere larger than the radiogalaxy itself (with a radius of about 50 arcsec centered on thegalaxy) This atmosphere is in good agreement geometricallywith the Capetti et al (2002) relation (ie the major axis of theellipsoidal atmosphere is co-aligned with the active lobes) butproving the presence of a hot atmosphere spectroscopically isdifficult An isothermal apec model requires T gt 7 keV andis otherwise poorly constrained a power law with Γ = 15 fitsthe spectrum well Since the emission region is large comparedto the radio galaxy it seems likely this is hot gas but a muchdeeper observation is necessary to establish this

REFERENCES

Adelman-McCarthy J et al 2008 ApJS 175 297Alexander P amp Leahy J P 1987 MNRAS 225 1Arnaud K A 1996 in ASP Conf Ser 101 Astronomical Data Analysis

Software and Systems V ed G H Jacoby amp J Barnes (San Francisco CAASP) 17

Ayres T R 2004 ApJ 608 957Balmaverde B Capetti A amp Grandi P 2006 AampA 451 35Baum S A Heckman T Bridle A van Breugel W amp Miley G 1988 ApJS

68 643Becker R H White R L amp Helfand D J 1995 ApJ 450 559Binney J amp Merrifield M 1998 Galactic Astronomy (Princeton Series in

Astrophysics Princeton NJ Princeton Univ Press)Black A R S Baum S A Leahy J P Perley R A Riley J M amp Scheuer

P A G 1992 MNRAS 256 186Bogdanovic T Reynolds C S amp Miller M C 2007 ApJ 661 L147Canosa C M Worrall D M Hardcastle M J amp Birkinshaw M 1999 MN-

RAS 310 30Capetti A Zamfir S Rossi P Bodo G Zanni C amp Massaglia S

2002 AampA 394 39Cheung C C 2007 AJ 133 2097Cheung C C Healey S E Landt H Kleijn G V amp Jordan A 2009 ApJS

181 548Cheung C C amp Springmann A 2007 in ASP Conf Ser 373 The Central

Engine of Active Galactic Nuclei ed L C Ho amp J-M Wang (San FranciscoCA ASP) 259

Condon J J Frayer D T amp Broderick J J 1991 AJ 101 362Croston J H Hardcastle M J Birkinshaw M amp Worrall D M 2003 MN-

RAS 346 1041Dennett-Thorpe J Scheuer P A G Laing R A Bridle A H Pooley

G G amp Reich W 2002 MNRAS 330 609Diehl S amp Statler T 2007 ApJ 668 150Donato D Sambruna R M amp Gliozzi M 2004 ApJ 617 915Efron B 1982 CBMS-NSF Regional Conf Ser in Applied Mathematics The

Jackknife the Bootstrap and Other Resampling Plans (Philadelphia PA Socfor Industrial amp Applied Mathematics)

Ekers R D Fanti R Lari C amp Parma P 1978 Nature 276 588Evans D A Hardcastle M J Croston J H Worrall D M amp Birkinshaw

M 2005 MNRAS 359 363Evans D A Worrall D M Hardcastle M J Kraft R P amp Birkinshaw M

2006 ApJ 642 96Fanaroff B L amp Riley J M 1974 MNRAS 167 31PFanti C Fanti R Gioia I M Lari C Parma P amp Ulrich M-H 1977

AampAS 29 279Fosbury R A E Morganti R Wilson W Ekers R D di Serego Alighieri

S amp Tadhunter C N 1998 MNRAS 296 701Ge J amp Owen F N 1994 AJ 108 1523Gopal-Krishna Biermann P L amp Wiita P J 2003 ApJ 594 L103Gopal-Krishna amp Wiita P J 2000 AampA 363 507Hardcastle M J Alexander P Pooley G G amp Riley J M 1996 MNRAS

278 273Hardcastle M J Birkinshaw M amp Worrall D M 2001 MNRAS 326 1499Hardcastle M J Croston J H amp Kraft R P 2007a ApJ 669 893Hardcastle M J Evans D A amp Croston J H 2006 MNRAS 370 1893Hardcastle M J Harris D E Worrall D M amp Birkinshaw M 2004 ApJ

612 729Hardcastle M J Kraft R P Worrall D M Croston J H Evans D A

Birkinshaw M amp Murray S S 2007b ApJ 662 166Hardcastle M J Sakelliou I amp Worrall D M 2005 MNRAS 359 1007Hardcastle M J Worrall D M Birkinshaw M Laing R A amp Bridle

A H 2002 MNRAS 334 182Isobe N Tashiro M Makishima K Iyomoto N Suzuki M Murakami

M M Mori M amp Abe K 2002 ApJ 580 L111Jeltema T E Binder B amp Mulchaey J S 2008 ApJ 679 1162Johnstone R M Allen S W Fabian A C amp Sanders J S 2002 MNRAS

336 299Kalberla P M W Burton W B Hartmann D Arnal E M Bajaja E

Morras R amp Poppel W G L 2005 AampA 440 775Klein U Mack K-H Gregorini L amp Parma P 1995 AampA 303 427Kraft R P Azcona J Forman W R Hardcastle M J Jones C amp Murray

S S 2006 ApJ 639 753Kraft R P Hardcastle M J Worrall D M amp Murray S S 2005 ApJ 622

149Laing R A Riley J M amp Longair M S 1983 MNRAS 204 151Lal D V amp Rao A P 2007 MNRAS 374 1085Lambas D G Maddox S J amp Loveday J 1992 MNRAS 258 404


Leahy J P Black A R S Dennett-Thorpe J Hardcastle M J KomissarovS Perley R A Riley J M amp Scheuer P A G 1997 MNRAS 291 20

Leahy J P amp Perley R A 1991 AJ 102 537Leahy J P amp Parma P 1992 in Extragalactic Radio Sources From Beams

to Jets ed J Roland H Sol amp G Pelletier (Cambridge Cambridge UnivPress) 307

Leahy J P amp Williams A G 1984 MNRAS 210 929Ly C de Young D S amp Bechtold J 2005 ApJ 618 609Magdziarz P amp Zdziarski A A 1995 MNRAS 273 837Martel A R et al 1999 ApJS 122 81Massaro F et al 2008 AAS HEAD meeting 10 2619Merritt D amp Ekers R D 2002 Science 297 1310Miller B P amp Brandt W N 2009 ApJ 695 755Murgia M Parma P de Ruiter H R Bondi M Ekers R D Fanti R amp

Fomalont E B 2001 AampA 380 102Neff S G Roberts L amp Hutchings J B 1995 ApJS 99 349Perley R A Dreher J W amp Cowan J J 1984 ApJ 285 L35Perlman E S Georganopoulos M May E M amp Kazanas D 2010 ApJ

708 1Press W H Teukolsky S A Vetterling W T amp Flannery B P 1992

Numerical Recipes in C The Art of Scientific Computing (2nd edCambridge Cambridge Univ Press)

Rees M 1978 Nature 275 516Reynolds C S Heinz S amp Begelman M C 2001 ApJ 549 L179Roettiger K Burns J Clarke D A amp Christiansen W A 1994 ApJ 421

L23

Rottmann H 2001 PhD thesis Univ BonnSambruna R M Gliozzi M Donato D Tavecchio F Cheung C C amp

Mushotzky R F 2004 AampA 414 885Saripalli L amp Subrahmanyan R 2009 ApJ 695 156Smith E P amp Heckman T M 1989 ApJ 341 685Smith D A Wilson A S Arnaud K A Terashima Y amp Young A J

2002 ApJ 565 195Sun M Jerius D amp Jones C 2005 ApJ 633 165Sun M Voit G M Donahue M Jones C Forman W amp Vikhlinin A

2009 ApJ 693 1142Thompson A R Clark B G Wade C M amp Napier P J 1980 ApJS 44

151Tremblay G R Chiaberge M Donzelli C J Quillen A C Capetti A

Sparks W B amp Maccheto F D 2007 ApJ 666 109van Breugel W Balick B Heckman T Miley G amp Helfand D 1983 AJ

88 1Wirth A Smarr L amp Gallagher J S 1982 AJ 87 602Worrall D M amp Birkinshaw M 2000 ApJ 530 719Worrall D M Birkinshaw M amp Cameron R A 1995 ApJ 449 93Wright E L 2006 PASP 118 1711Young A J Wilson A S Terashima Y Arnaud K A amp Smith D A

2002 ApJ 564 176Young A J Wilson A S Tingay S J amp Heinz S 2005 ApJ 622

830Zier C 2005 MNRAS 364 583Zier C amp Biermann P L 2001 AampA 377 23

1 INTRODUCTION



22 Data Reduction




3 THERMAL ATMOSPHERE PROPERTIES

31 Ellipse Fitting





APPENDIX NOTES ON INDIVIDUAL GALAXIES

A1 XRGs


A3 Unused XRGs

REFERENCES


hereafter C02) The buoyant backflow model supposes that thebuoyancy of the relativistic plasma cocoon in the interstellar orintragroupintracluster medium (ISM or IGMICM) producesthe additional wings Because of the collimation seen in the moredramatic XRG wings we refer to them hereafter as ldquosecondarylobesrdquo even though if the hydrodynamic premise is correct theyare not of the same character as the primary lobes

C02 propose a variant model in which backflowing plasmaconfined by an envelope of hot gas continues to aggregate untilthe cocoon of radio plasma is significantly overpressured atwhich point it blows out of the confining medium at its weakestpoint Supposing that the confining medium is the ISM of anelliptical galaxy if the jet is aligned along the major axis ofthe galaxy then the cocoon may become overpressured beforethe jet bores through the ISM and the radio plasma will blowout along the minor axis of the galaxy forming the secondarylobes Conversely if the jet is oriented along the minor axis ofthe galaxy then backflow will either escape along the same axisor the jet will escape the ISM before the cocoon can becomeoverpressured C02 cite an intriguing correlation between theorientation of the secondary lobes in XRGs and the minor axisof the host galaxy as evidence for their model which they furthersupport with two-dimensional hydrodynamic simulations In afollow-up study including ldquonormalrdquo radio galaxies S09 findthat the primary lobes of giant radio galaxies are preferentiallyaligned along the minor axis of the host whereas they extendthe original C02 result to a larger XRG sample Althoughthe observed geometric correlation is strong much of thepotentially relevant physics is absent in the C02 simulationsand Kraft et al (2005) note that the buoyant backflow modelcan explain the observed correlation by assuming an anisotropicmedium to divert the backflow Moreover it is unclear whetherreal radio lobes are actually overpressured Reynolds et al(2001) argue that an overpressured cocoon is inflated early onbut in the buoyant backflow model the secondary lobes areformed later In either case the geometric correlation favors ahydrodynamic origin for the secondary lobes in the absence ofan explanation for a relationship between the angular momentaof two merging SMBHs and large-scale structure of the galaxyFor the remainder of this paper we refer to the ldquoC02 geometryrdquoto describe the correlation noted in XRGs and the proposedgeometry of jet alignment that would produce them

There are additional XRG formation models which aresimilar to the ones presented above in that they rely solely oneither the black hole(s) involved or jetndashgas interaction Theseinclude the hypothesis that X- and Z-shaped distortions arise viagravitational interaction with another galaxy (Wirth et al 1982van Breugel et al 1983) the idea that the jets are diverted by theISM of a smaller merging galaxy (Gopal-Krishna et al 2003Zier 2005) and the aforementioned Lal amp Rao (2007) proposalthat both lobes are powered by active jets Because these modelsare not as easily probed by the hot gas we focus on the backflowmodels hereafter

In this paper we seek to characterize the properties of the hotgas in these systems and determine whether the C02 opticalndashradio geometric correlation also exists in the X-ray band Oneassumption of the C02 proposal is that the stellar distributiontraces the hot gas which makes up the confining medium Wewill test this assumption directly by determining the extent towhich optical and X-ray morphology are correlated As a paral-lel study we present the results from new and archival ChandraX-ray Observatory observations of XRGs and investigatewhether the hot gas in XRG systems differs from that in a

comparison sample of archival Chandra observations of ldquonor-malrdquo FR I and II galaxies (taken largely from the 3CRR catalogLaing et al 1983)

Any observational study of XRGs is necessarily limited bythe small number of known and candidate sources Our studyis further limited by two important factors (1) the hot gas sur-rounding radio galaxies becomes increasingly difficult to char-acterize at higher redshift and (2) useful X-ray data do not existfor most XRGs These considerations strongly constrain ourconclusions We therefore discuss in detail our target selectioncriteria in Section 2 as well as the observational parametersand reduction techniques applied to the data In Section 3 wediscuss our primary analysis of the morphology of the hot gasand in Section 4 we discuss the X-ray spectra of the AGN InSection 5 we summarize our results and interpretations

Throughout this paper we adopt the Wilkinson MicrowaveAnisotropy Probe (WMAP) values of H0 = 71 km sminus1 Mpcminus1ΩM = 027 and Ωvac = 073 with flat geometry We calculateequivalent angular scale and distances at redshift using theonline calculator provided by Wright (2006) and for Galacticabsorption we use the online HEASARC NH calculator withvalues from the LeidenArgentineBonn survey (Kalberla et al2005)4


Chandra is well suited to a study of the hot environmentsof radio galaxies thanks to its high sensitivity 0primeprime5 spatialresolution and 03ndash10 keV bandwidth Chandra has also beenable to resolve X-ray emission associated with the radio lobesinto hot spots and jets (Hardcastle et al 2004) distinguishingthis emission from the gaseous halos is especially important forour purposes

Our analysis sample of Chandra data consists of 18 compari-son sample galaxies and 8 XRGs (Figures 1 and 2 with observa-tional parameters in Table 1) In this section we describe howwe arrived at this sample starting with the preliminary selec-tion criteria for the XRG and comparison samples from radiodata and availability in the Chandra archive (Section 21) Afterreducing these data we rejected a number of galaxies due tolow quality or pileup (Section 22) then used spectral fitting tofind those galaxies where the diffuse gas dominates the photoncount in the relevant regions (Section 23) These are the galax-ies we include in our final sample (Table 1) Figures 1 and 2are discussed along with the radio and optical data we use inSection 24

We note that many of the archival data sets have been pub-lished and references are provided in Table 1 where availableOur goal is not to exhaustively study any individual sourceNotes on individual sources are found in the Appendix


The most complete compilation of known and candidateX-shaped sources in the literature is that of Cheung (2007)who used the NRAO5 Very Large Array (VLA Thompson et al1980) Faint Images of the Radio Sky at Twenty cm (FIRSTBecker et al 1995) data to identify the candidate XRGs Forthis paper we define XRGs as comprising all radio galaxies inCheung (2007) that have a wing length exceeding 80 of the

4 See httpheasarcgsfcnasagovcgi-binToolsw3nhw3nhpl5 The National Radio Astronomy Observatory is a facility of the NationalScience Foundation operated under cooperative agreement by AssociatedUniversities Inc
















22 Data Reduction






XRGs


Comparison sample

























XRGs














XRGs



IGM (l) 75 75 13+03minus01 03+04

minus02 11 024 apec 47 20223



IGM 166 94 36 plusmn 04 08 (f) 19 11 apec 10 941100


IGM 97 40 06 plusmn 02 10 (f) 037 004 apec 09 34336




minus01 10 (f) 10 01 apec+PL 82 4510

Comparison sample




IGM 30 30 20+05minus02 04+02

minus01 20 069 apec 13 1431138


ICM 56 30 8+6minus3 10 (f) 12 16 apec 17 80986


3C 66B ISM 9 9 0022 767 061+006minus004 03+1

minus01 72 071 apec(+IGM) 036 49842


IGM 75 75 4+4minus1 10 (f) 08 05 apec 08 18219




T2 = 09 plusmn 006 10 (f)



3C 98 IGM 46 31 0030 108 11+03minus02 02+04

minus01 18 032 apec 08 8511





Thigh = 18 plusmn 7



T2 = 033+03minus005 10 (f)



T2 = 12+03minus02 10 (f)















Working Sample

B2 1040+31A 015 153 159

PKS 1422+26 016 118 92

NGC 326 004 0 153 b 120 1353C 403 027 a 025 39 35 39 72 85 794C +0058 051 139 65

3C 192 002 a 0 119 95 b 123 125 1233C 433 030 047 167 145 169 1643C 315 037 a 046 44 35 33 12 10 8

Unused XRGs

4C +3225 012 a 015 90 90 84 61 60 644C +4829 003 0 127 b 179 1703C 1361 039 a 037 101 100 117 106 110 139J1101+1640 034 029 62 64 113 1143C 2231 042 a 045 43 40 40 7 15 15


31 Ellipse Fitting












() () () () () ()

XRGs


Comparison sample









() () ()

XRGs


Comparison sample

3C 449 03 plusmn 01 41 plusmn 12 9

3C 31 018 plusmn 001 123 plusmn 4 160

3C 296 023 plusmn 004 121 plusmn 8 35


3C 338 0243 plusmn 0002 65 plusmn 6 90

3C 465 037 plusmn 002 53 plusmn 3 126


3C 445 03 plusmn 01 77 plusmn 8 169

3C 285 028 plusmn 006 163 plusmn 9 73

3C 452 043 plusmn 003 83 plusmn 2 78

3C 388 (l) 013 plusmn 002 65 plusmn 6 55

3C 388 (s) 0088 plusmn 0005 133 plusmn 18 55















































XRGs



Comparison sample








Facilities CXO VLA

APPENDIX


A1 XRGs





































A3 Unused XRGs


S = S0 +

(s2 + 2

3

)plusmn ΔS


ΔS equiv s

radicmax[(N minus 1

4B) 0] + 1


min[B01 1]

7s2 +

radicBs +


7

]= 0
















REFERENCES






































L23










1 INTRODUCTION



22 Data Reduction





31 Ellipse Fitting






A1 XRGs


A3 Unused XRGs

REFERENCES
















22 Data Reduction






XRGs


Comparison sample

























XRGs














XRGs



IGM (l) 75 75 13+03minus01 03+04

minus02 11 024 apec 47 20223



IGM 166 94 36 plusmn 04 08 (f) 19 11 apec 10 941100


IGM 97 40 06 plusmn 02 10 (f) 037 004 apec 09 34336




minus01 10 (f) 10 01 apec+PL 82 4510

Comparison sample




IGM 30 30 20+05minus02 04+02

minus01 20 069 apec 13 1431138


ICM 56 30 8+6minus3 10 (f) 12 16 apec 17 80986


3C 66B ISM 9 9 0022 767 061+006minus004 03+1

minus01 72 071 apec(+IGM) 036 49842


IGM 75 75 4+4minus1 10 (f) 08 05 apec 08 18219




T2 = 09 plusmn 006 10 (f)



3C 98 IGM 46 31 0030 108 11+03minus02 02+04

minus01 18 032 apec 08 8511





Thigh = 18 plusmn 7



T2 = 033+03minus005 10 (f)



T2 = 12+03minus02 10 (f)















Working Sample

B2 1040+31A 015 153 159

PKS 1422+26 016 118 92

NGC 326 004 0 153 b 120 1353C 403 027 a 025 39 35 39 72 85 794C +0058 051 139 65

3C 192 002 a 0 119 95 b 123 125 1233C 433 030 047 167 145 169 1643C 315 037 a 046 44 35 33 12 10 8

Unused XRGs

4C +3225 012 a 015 90 90 84 61 60 644C +4829 003 0 127 b 179 1703C 1361 039 a 037 101 100 117 106 110 139J1101+1640 034 029 62 64 113 1143C 2231 042 a 045 43 40 40 7 15 15


31 Ellipse Fitting












() () () () () ()

XRGs


Comparison sample









() () ()

XRGs


Comparison sample

3C 449 03 plusmn 01 41 plusmn 12 9

3C 31 018 plusmn 001 123 plusmn 4 160

3C 296 023 plusmn 004 121 plusmn 8 35


3C 338 0243 plusmn 0002 65 plusmn 6 90

3C 465 037 plusmn 002 53 plusmn 3 126


3C 445 03 plusmn 01 77 plusmn 8 169

3C 285 028 plusmn 006 163 plusmn 9 73

3C 452 043 plusmn 003 83 plusmn 2 78

3C 388 (l) 013 plusmn 002 65 plusmn 6 55

3C 388 (s) 0088 plusmn 0005 133 plusmn 18 55















































XRGs



Comparison sample








Facilities CXO VLA

APPENDIX


A1 XRGs





































A3 Unused XRGs


S = S0 +

(s2 + 2

3

)plusmn ΔS


ΔS equiv s

radicmax[(N minus 1

4B) 0] + 1


min[B01 1]

7s2 +

radicBs +


7

]= 0
















REFERENCES






































L23










1 INTRODUCTION



22 Data Reduction





31 Ellipse Fitting






A1 XRGs


A3 Unused XRGs

REFERENCES




XRGs


Comparison sample

























XRGs














XRGs



IGM (l) 75 75 13+03minus01 03+04

minus02 11 024 apec 47 20223



IGM 166 94 36 plusmn 04 08 (f) 19 11 apec 10 941100


IGM 97 40 06 plusmn 02 10 (f) 037 004 apec 09 34336




minus01 10 (f) 10 01 apec+PL 82 4510

Comparison sample




IGM 30 30 20+05minus02 04+02

minus01 20 069 apec 13 1431138


ICM 56 30 8+6minus3 10 (f) 12 16 apec 17 80986


3C 66B ISM 9 9 0022 767 061+006minus004 03+1

minus01 72 071 apec(+IGM) 036 49842


IGM 75 75 4+4minus1 10 (f) 08 05 apec 08 18219




T2 = 09 plusmn 006 10 (f)



3C 98 IGM 46 31 0030 108 11+03minus02 02+04

minus01 18 032 apec 08 8511





Thigh = 18 plusmn 7



T2 = 033+03minus005 10 (f)



T2 = 12+03minus02 10 (f)















Working Sample

B2 1040+31A 015 153 159

PKS 1422+26 016 118 92

NGC 326 004 0 153 b 120 1353C 403 027 a 025 39 35 39 72 85 794C +0058 051 139 65

3C 192 002 a 0 119 95 b 123 125 1233C 433 030 047 167 145 169 1643C 315 037 a 046 44 35 33 12 10 8

Unused XRGs

4C +3225 012 a 015 90 90 84 61 60 644C +4829 003 0 127 b 179 1703C 1361 039 a 037 101 100 117 106 110 139J1101+1640 034 029 62 64 113 1143C 2231 042 a 045 43 40 40 7 15 15


31 Ellipse Fitting












() () () () () ()

XRGs


Comparison sample









() () ()

XRGs


Comparison sample

3C 449 03 plusmn 01 41 plusmn 12 9

3C 31 018 plusmn 001 123 plusmn 4 160

3C 296 023 plusmn 004 121 plusmn 8 35


3C 338 0243 plusmn 0002 65 plusmn 6 90

3C 465 037 plusmn 002 53 plusmn 3 126


3C 445 03 plusmn 01 77 plusmn 8 169

3C 285 028 plusmn 006 163 plusmn 9 73

3C 452 043 plusmn 003 83 plusmn 2 78

3C 388 (l) 013 plusmn 002 65 plusmn 6 55

3C 388 (s) 0088 plusmn 0005 133 plusmn 18 55















































XRGs



Comparison sample








Facilities CXO VLA

APPENDIX


A1 XRGs





































A3 Unused XRGs


S = S0 +

(s2 + 2

3

)plusmn ΔS


ΔS equiv s

radicmax[(N minus 1

4B) 0] + 1


min[B01 1]

7s2 +

radicBs +


7

]= 0
















REFERENCES






































L23










1 INTRODUCTION



22 Data Reduction





31 Ellipse Fitting






A1 XRGs


A3 Unused XRGs

REFERENCES
















XRGs














XRGs



IGM (l) 75 75 13+03minus01 03+04

minus02 11 024 apec 47 20223



IGM 166 94 36 plusmn 04 08 (f) 19 11 apec 10 941100


IGM 97 40 06 plusmn 02 10 (f) 037 004 apec 09 34336




minus01 10 (f) 10 01 apec+PL 82 4510

Comparison sample




IGM 30 30 20+05minus02 04+02

minus01 20 069 apec 13 1431138


ICM 56 30 8+6minus3 10 (f) 12 16 apec 17 80986


3C 66B ISM 9 9 0022 767 061+006minus004 03+1

minus01 72 071 apec(+IGM) 036 49842


IGM 75 75 4+4minus1 10 (f) 08 05 apec 08 18219




T2 = 09 plusmn 006 10 (f)



3C 98 IGM 46 31 0030 108 11+03minus02 02+04

minus01 18 032 apec 08 8511





Thigh = 18 plusmn 7



T2 = 033+03minus005 10 (f)



T2 = 12+03minus02 10 (f)















Working Sample

B2 1040+31A 015 153 159

PKS 1422+26 016 118 92

NGC 326 004 0 153 b 120 1353C 403 027 a 025 39 35 39 72 85 794C +0058 051 139 65

3C 192 002 a 0 119 95 b 123 125 1233C 433 030 047 167 145 169 1643C 315 037 a 046 44 35 33 12 10 8

Unused XRGs

4C +3225 012 a 015 90 90 84 61 60 644C +4829 003 0 127 b 179 1703C 1361 039 a 037 101 100 117 106 110 139J1101+1640 034 029 62 64 113 1143C 2231 042 a 045 43 40 40 7 15 15


31 Ellipse Fitting












() () () () () ()

XRGs


Comparison sample









() () ()

XRGs


Comparison sample

3C 449 03 plusmn 01 41 plusmn 12 9

3C 31 018 plusmn 001 123 plusmn 4 160

3C 296 023 plusmn 004 121 plusmn 8 35


3C 338 0243 plusmn 0002 65 plusmn 6 90

3C 465 037 plusmn 002 53 plusmn 3 126


3C 445 03 plusmn 01 77 plusmn 8 169

3C 285 028 plusmn 006 163 plusmn 9 73

3C 452 043 plusmn 003 83 plusmn 2 78

3C 388 (l) 013 plusmn 002 65 plusmn 6 55

3C 388 (s) 0088 plusmn 0005 133 plusmn 18 55















































XRGs



Comparison sample








Facilities CXO VLA

APPENDIX


A1 XRGs





































A3 Unused XRGs


S = S0 +

(s2 + 2

3

)plusmn ΔS


ΔS equiv s

radicmax[(N minus 1

4B) 0] + 1


min[B01 1]

7s2 +

radicBs +


7

]= 0
















REFERENCES






































L23










1 INTRODUCTION



22 Data Reduction





31 Ellipse Fitting






A1 XRGs


A3 Unused XRGs

REFERENCES





XRGs



IGM (l) 75 75 13+03minus01 03+04

minus02 11 024 apec 47 20223



IGM 166 94 36 plusmn 04 08 (f) 19 11 apec 10 941100


IGM 97 40 06 plusmn 02 10 (f) 037 004 apec 09 34336




minus01 10 (f) 10 01 apec+PL 82 4510

Comparison sample




IGM 30 30 20+05minus02 04+02

minus01 20 069 apec 13 1431138


ICM 56 30 8+6minus3 10 (f) 12 16 apec 17 80986


3C 66B ISM 9 9 0022 767 061+006minus004 03+1

minus01 72 071 apec(+IGM) 036 49842


IGM 75 75 4+4minus1 10 (f) 08 05 apec 08 18219




T2 = 09 plusmn 006 10 (f)



3C 98 IGM 46 31 0030 108 11+03minus02 02+04

minus01 18 032 apec 08 8511





Thigh = 18 plusmn 7



T2 = 033+03minus005 10 (f)



T2 = 12+03minus02 10 (f)















Working Sample

B2 1040+31A 015 153 159

PKS 1422+26 016 118 92

NGC 326 004 0 153 b 120 1353C 403 027 a 025 39 35 39 72 85 794C +0058 051 139 65

3C 192 002 a 0 119 95 b 123 125 1233C 433 030 047 167 145 169 1643C 315 037 a 046 44 35 33 12 10 8

Unused XRGs

4C +3225 012 a 015 90 90 84 61 60 644C +4829 003 0 127 b 179 1703C 1361 039 a 037 101 100 117 106 110 139J1101+1640 034 029 62 64 113 1143C 2231 042 a 045 43 40 40 7 15 15


31 Ellipse Fitting












() () () () () ()

XRGs


Comparison sample









() () ()

XRGs


Comparison sample

3C 449 03 plusmn 01 41 plusmn 12 9

3C 31 018 plusmn 001 123 plusmn 4 160

3C 296 023 plusmn 004 121 plusmn 8 35


3C 338 0243 plusmn 0002 65 plusmn 6 90

3C 465 037 plusmn 002 53 plusmn 3 126


3C 445 03 plusmn 01 77 plusmn 8 169

3C 285 028 plusmn 006 163 plusmn 9 73

3C 452 043 plusmn 003 83 plusmn 2 78

3C 388 (l) 013 plusmn 002 65 plusmn 6 55

3C 388 (s) 0088 plusmn 0005 133 plusmn 18 55















































XRGs



Comparison sample








Facilities CXO VLA

APPENDIX


A1 XRGs





































A3 Unused XRGs


S = S0 +

(s2 + 2

3

)plusmn ΔS


ΔS equiv s

radicmax[(N minus 1

4B) 0] + 1


min[B01 1]

7s2 +

radicBs +


7

]= 0
















REFERENCES






































L23










1 INTRODUCTION



22 Data Reduction





31 Ellipse Fitting






A1 XRGs


A3 Unused XRGs

REFERENCES










Working Sample

B2 1040+31A 015 153 159

PKS 1422+26 016 118 92

NGC 326 004 0 153 b 120 1353C 403 027 a 025 39 35 39 72 85 794C +0058 051 139 65

3C 192 002 a 0 119 95 b 123 125 1233C 433 030 047 167 145 169 1643C 315 037 a 046 44 35 33 12 10 8

Unused XRGs

4C +3225 012 a 015 90 90 84 61 60 644C +4829 003 0 127 b 179 1703C 1361 039 a 037 101 100 117 106 110 139J1101+1640 034 029 62 64 113 1143C 2231 042 a 045 43 40 40 7 15 15


31 Ellipse Fitting












() () () () () ()

XRGs


Comparison sample









() () ()

XRGs


Comparison sample

3C 449 03 plusmn 01 41 plusmn 12 9

3C 31 018 plusmn 001 123 plusmn 4 160

3C 296 023 plusmn 004 121 plusmn 8 35


3C 338 0243 plusmn 0002 65 plusmn 6 90

3C 465 037 plusmn 002 53 plusmn 3 126


3C 445 03 plusmn 01 77 plusmn 8 169

3C 285 028 plusmn 006 163 plusmn 9 73

3C 452 043 plusmn 003 83 plusmn 2 78

3C 388 (l) 013 plusmn 002 65 plusmn 6 55

3C 388 (s) 0088 plusmn 0005 133 plusmn 18 55















































XRGs



Comparison sample








Facilities CXO VLA

APPENDIX


A1 XRGs





































A3 Unused XRGs


S = S0 +

(s2 + 2

3

)plusmn ΔS


ΔS equiv s

radicmax[(N minus 1

4B) 0] + 1


min[B01 1]

7s2 +

radicBs +


7

]= 0
















REFERENCES






































L23










1 INTRODUCTION



22 Data Reduction





31 Ellipse Fitting






A1 XRGs


A3 Unused XRGs

REFERENCES




() () () () () ()

XRGs


Comparison sample









() () ()

XRGs


Comparison sample

3C 449 03 plusmn 01 41 plusmn 12 9

3C 31 018 plusmn 001 123 plusmn 4 160

3C 296 023 plusmn 004 121 plusmn 8 35


3C 338 0243 plusmn 0002 65 plusmn 6 90

3C 465 037 plusmn 002 53 plusmn 3 126


3C 445 03 plusmn 01 77 plusmn 8 169

3C 285 028 plusmn 006 163 plusmn 9 73

3C 452 043 plusmn 003 83 plusmn 2 78

3C 388 (l) 013 plusmn 002 65 plusmn 6 55

3C 388 (s) 0088 plusmn 0005 133 plusmn 18 55















































XRGs



Comparison sample








Facilities CXO VLA

APPENDIX


A1 XRGs





































A3 Unused XRGs


S = S0 +

(s2 + 2

3

)plusmn ΔS


ΔS equiv s

radicmax[(N minus 1

4B) 0] + 1


min[B01 1]

7s2 +

radicBs +


7

]= 0
















REFERENCES






































L23










1 INTRODUCTION



22 Data Reduction





31 Ellipse Fitting






A1 XRGs


A3 Unused XRGs

REFERENCES













































XRGs



Comparison sample








Facilities CXO VLA

APPENDIX


A1 XRGs





































A3 Unused XRGs


S = S0 +

(s2 + 2

3

)plusmn ΔS


ΔS equiv s

radicmax[(N minus 1

4B) 0] + 1


min[B01 1]

7s2 +

radicBs +


7

]= 0
















REFERENCES






































L23










1 INTRODUCTION



22 Data Reduction





31 Ellipse Fitting






A1 XRGs


A3 Unused XRGs

REFERENCES




































A3 Unused XRGs


S = S0 +

(s2 + 2

3

)plusmn ΔS


ΔS equiv s

radicmax[(N minus 1

4B) 0] + 1


min[B01 1]

7s2 +

radicBs +


7

]= 0
















REFERENCES






































L23










1 INTRODUCTION



22 Data Reduction





31 Ellipse Fitting






A1 XRGs


A3 Unused XRGs

REFERENCES











REFERENCES






































L23










1 INTRODUCTION



22 Data Reduction





31 Ellipse Fitting






A1 XRGs


A3 Unused XRGs

REFERENCES










L23










1 INTRODUCTION



22 Data Reduction





31 Ellipse Fitting






A1 XRGs


A3 Unused XRGs

REFERENCES

the chandra view of nearby x-shaped radio galaxiesmiller/reprints/hodges10a.pdffainter pair of wings...

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