granada, may 27ththe x-ray universe 2008 x-ray selected type-2 qsos: high luminosity in heavily...

Granada, May 27thGranada, May 27th The X-ray Universe 2008The X-ray Universe 2008

X-ray selected Type-2 QSOs: high luminosity in heavily obscured AGN

Vincenzo MainieriESO

G. Hasinger, M. Brusa, N. Cappelluti, K. Iwasawa, M. SalvatoM. Bolzonella, A. Comastri, F. Fiore, R. Gilli,

S. Lilly, J. Silverman, G. Zamorani+ COSMOS

-


OUTLINE:

COSMOS Survey

Selection criteria

Comparison with SDSS QSO-2

Comparison with MIR selection criteria

Multi-wavelength properties

Host galaxy properties•Morphology•Stellar masses•Star formation rates

Conclusions


Why studying QSO-2?

Quantifying the population of obscured quasars is essential for many applications:

• relating the present mass density of BH to the accretion history of the entire AGN population (e.g. Soltan 1982; Yu & Tremaine 2002; Marconi et al. 2004)

• understand the origin of the cosmic XRB (e.g. Comastri et al. 1995; Gilli et al. 2007)

• studying the effects of luminosity on AGN structure (e.g. Lawrence 1991; Urry & Padovani 1995; Hopkins et al. 2006; Hasinger 2008)


QSO-2 selection criteria

• Radio: radio-loud QSO-2 have been know for decades from radio surveys, narrow line radio galaxies (see McCarthy 1993 for a review). They probably represents ~10% of the whole population

• Optical : candidates selected as objects with narrow (FWHM<1000 km s-1) permitted emission lines and high ionization line ratios characteristic of non-stellar ionizing radiation (e.g. Djorgovski et al. 2001, DPSS)

• SDSS (Zakamska et al. 2003; Reyes et al. 2008): 887 QSO-2 with z<0.83MB<-23 --> L[OIII] > 3 x 108 LSUN

• X-ray: hard X-ray spectra and high X-ray luminosity NH>1022 cm-2

LX>1044 erg s-1

(e.g. Norman et al. 2001, Dawson et al. 2001, Mainieri et al. 2002, Stern et al. 2002, Della Ceca et al. 2003, Perola et al. 2004, Szokoly et al. 2004, Barger et al. 2005, Mateos et al. 2005, Krumpe et al. 2008, ….)

• Mid-IR: the emission absorbed by the circumnuclear material is thermally re-emitted in the IR (e.g. Lacy et al. 2005, Stern et al. 2005, Martinez-Sansigre et al. 2006, Polletta et al. 2007, Daddi et al. 2008, Fiore et al. 2008)


http://cosmos.astro.caltech.edu/ PI N. Scoville

http://cosmos.astro.caltech.edu/


+ MAMBO, CFHT, Bolocam and (future) others

COSMOS major components (in order of appearance) :

HST/ACS (I-band – 590 orbits – I(AB)~27)

2002-2003: Subaru imaging (~25 nights - b,v,r,i,z=26/27) VLA (265 hours – 24 μJy) GALEX deep (200 ks, AB~25) XMM-Newton (800 ks – 10-15 cgs)

2004-2005: XMM-Newton (600 ks) VLT (540 hours) & Magellan (12+ nights) SPITZER-IRAC (200 hours - ~1 μJy)

2006: SPITZER-MIPS (200 hours - ~70 μJy) Chandra (1.8 Ms)

http://www.astro.caltech.edu/cosmos/

XMM-NewtonPI: G. Hasinger

soft 0.5-2.0 keVmedium 2.0-4.5 keV

hard 4.5-10.0 keV

Cosmos Survey2 deg2 (PI: N. Scoville)

http://cosmos.astro.caltech.eduApJS special issue vol. 172

http://cosmos.astro.caltech.edu/

XMM-COSMOS 2 deg2

-16

-15

-14

-13

Flux 2

-10 k

eV

(cg

s)CDFN-CDFS 0.1deg2 Barger et al. 2003; Szokoly et al. 2004

EGS/AEGIS 0.5deg2Nandra et al. 2006

HELLAS2XMM 1.4 deg2Fiore et al. 20003Cocchia et al. 2006Champ 1.5deg2Silverman et al. 2005

XBOOTES 9 deg2Murray et al. 2005, Brand et al. 2005

Relative sizes of X-ray surveys

SEXSI 2 deg2 Eckart et al. 2006

Area(see Brandt & Hasinger 2005 review (ARA&A 43, 827)

E-CDFS 0.3deg2 Lehmer et al. 2005

ELAIS-S1 0.5deg2Puccetti et al. 2006


180 counts

X-ray spectral analysis

Fit statisticCash-statistic with a binning of 1 count per bin: it recovers the input values better than 2 for faint sources (see also Tozzi et al. 2006 and Krumpe et al. 2008)

Input models PL : powerlawAPL: powerlaw + intrinsic absorption at the

redshift of the source

Additional component to account for the photoelectric absorption due to the

Galactic column density (NHGal~2.7 x 1020 cm-2,

Dickey & Lockman 1990)

Soft excess: black body model or a double powerlaw (pcfabs)

FeK line: Gaussian centered at 6.4 keV rest-frame

We have used the F-test to measure the significance for each spectral component (confidence threshold of 95%).

X-ray zoo

[0.5-2] [2-4.5] [4.5-10] keV

PL

APL

APL+soft

APL+Fe


QSO-2: X-ray selection criteria

•LXdeabs[0.5-10 keV]>1044erg/s

•NH>1022 cm-2

121 QSO-2

Probably the largest sample of X-ray selected QSO-2 : 14 (Krumpe et al. 2008) 6 (Mainieri et al. 2002) 10 (Szokoly et al. 2004) 6 (Mateos et al. 2005)

SDSS: 887


QSO-2 : NH distribution


NH versus Redshift

Statistical fluctuations in the X-ray spectrum can lead to spurious high values of NH at high redshift (e.g. Tozzi et al. 2006, Akylas et al. 2006).

We find no trend of the NH values with redshift.


25 arcsec

AC

S/H

ST

z=0.1248 (SDSS spectrum)

pexrav+gauss

Compton-thick


Stacked X-ray spectrum

• Only the rest-frame 2.1-10.1 keV band was used for each spectrum.

• Spectral binning was designed to match a fixed rest-frame 200eV intervals.

• The total accumulated counts are 4763.3

•Assuming =1.8 --> NH=(3.7± 0.6) 1022 cm-2

•EW(FeK)~200 eV


IAB=24

X-ray to optical flux ratios

For IAB<24, 42% of the QSO-2 have spectroscopic redshifts. Above IAB=24, only photometric redshifts are available.

10% of the QSO-2 have X/O>10


Photometric redshifts for AGN

• Improved templates, including hybrids of galaxy+AGN• Photometry from >30 bands (SDSS, Subaru including IB, CFHT, J, K, IRAC)

= 0.017

Less than 10% of catastrophic errors

Salvato et al., 2008


ESO -ESO -

PI S. LillyPI S. Lilly


QSO-2 Redshift distribution

•34 spectroscopic redshifts (28%) : 17 from IMACS/Magellan, 13 from zCOSMOS VIMOS/VLT and 4 from DEIMOS/Keck.• 15 out of 34 (44%) do not show any sign of AGN activity from the optical spectra.

zspec


X-ray vs L[OIII]5007 luminosity

• X-ray selected QSO-2 have lower L[OIII] compared to optically selected ones.• Their L2-10/L[OIII] ratios are higher than opticaly seleted AGN : <log(L2-10/L[OIII]>=0.6 for Seyfert-2 from Heckman et al. (2005)• Their L2-10/L[OIII] ratios are consistent with what observed for local sample of X-ray selected AGN: <log(L2-10/L[OIII]>=2.2 from Heckman et al. (2005)

We measured L[OIII]5007 for 6 QSO-2 and 112 AGN:


X-ray vs optical QSO-2: optical colors

Stellar locus

z~0.8


z=0-2 z=2-7

QSO-2: X-ray vs MIR selection

Lacy’s wedge Stern’s wedge

MIR selection: good (86% of X-ray QSO-2 inside Lacy’s wedge, 75% of X-ray QSO-2 inside Stern’s wedge) …but not perfect :high contamination by starburst (all z) and elliptical (z>2) galaxies

http://www.exp-astro.phys.ethz.ch/ZEST/

Host galaxy morphology

Zurich Estimator of Strutural Type (Scarlata et al. 2007, ApJS, 172, 406)

• Five non-parametric diagnostics (asymmetry A, concentration C, Gini coefficient G, 2nd order moment of the brightest 20% of galaxy pixels M20, ellipticity )• Sersic index n

ZEST morphological type:

• 1 Early type

• 2 Disk

• 2.0 Bulge dominated disk (n>2.5)

• 2.1 … (1.25<n<2.5)

• 2.2 … (0.75<n<1.25)

• 2.3 Pure disk galaxy (n<0.75)

• 3 Irregular

Since optical radiation from QSO-2 is heavily obscured there is no

significant contamination from the bright central source


ZEST morphological classification for 29 QSO-2

Early10%

Disk55%

Irregular35%

Host galaxy morphology

ELL SPIRAL IRR

B/D

Comparison sample of 36000 galaxies morphologically classified

The majority the QSO-2 host galaxies are late type or irregular. Several of the irregular hosts can be described as undergoing merger activity or show tidal debris.

SDSS QSO-2 (Zakamska et al. 2006):•6/9 de Vaucouleurs light profiles•1/9 disk dominated•2/9 marginal disk detection


1.0

2.0

2.1

2.2

3.0

ACS/HST F814 W (5”x5”)


1.4 GHz (2’x2’)Radio Loudness

R=log(f1.4GHz /fV)

Radio loudness defined in terms of the ratio of radio flux to broadband optical flux (e.g. Kellermann et al. 1989): assuming r~0.7 --> R~1.4

23/121 (~19%) radio loud QSO-2


Type-2 QSO: Spectral Energy Distribution [0.1-20 m]

The mean SED of our QSO-2 is consistent with the typical SED of Type-2 AGN (Schmitt et al. 1997) and rule out Type-1 SED in which L rises by ~2 orders of magnitude below 1 m (Elvis et al. 1994).


Tyep-2 QSOs: stellar masses of the host galaxies

The majority (75%) of QSO-2 have stellar masses above log M*~10.5MSUN. This is similar to the characteristic mass for obscured AGN (Kauffmann et al. 2003) and radio-loud AGN (Best et al. 2005) in the SDSS. It is also consistent with the more general result that the fraction of galaxies hosting AGN increases with the stellar mass ( e.g. Silverman et al. 2008). Comparison sample of 22157

galaxies with 0.7<z<3.7

Estimate of the stellar masses

Bolzonella et al. 2008: SED fitting to the multi-band photometry in COSMOS (U,B,V,g,r,I,z,K,3.6,4.5):

BC03/CB07/M05 libraries + Chabrier/Kroupa IMF+ smooth exponential SFHs


Tyep-2 QSOs: star formation rates of the host galaxies

Comparison sample of 22157 galaxies with 0.7<z<3.7

Estimate of the stellar masses

Bolzonella et al. 2008: SED fitting to the multi-band photometry in COSMOS (U,B,V,g,r,I,z,K,3.6,4.5):

BC03/CB07/M05 libraries + Chabrier/Kroupa IMF+ smooth exponential SFHs

The host galaxies of QSO-2 have ongoing star formation higher that the comparison sample of galaxies. This is consistent with the host galaxies be manly late types or irregulars. 60% of QSO-2 have SFR in range 1-1000 MSUN/yr.


Conclusions

• We have selected a large (121) sample of QSO-2 based on their X-ray properties (NH>1022cm-2 & LX>1044 erg/s) on a wide redshift range: 0.6<z<3.7

• Their L2-10/L[OIII] ratios are higher than optically selected AGN-2.

• Different selection methods (radio, mid-IR, optical, X-ray) of QSO-2 are affected by different selection effect therefore select different samples.

• The majority the QSO-2 host galaxies are late type or irregular. Several can be described as undergoing merger activity or show tidal debris.

• The mean SED of our QSO-2 is consistent with the typical SED of Type-2 AGN.

• The majority (75%) of QSO-2 host galaxies have stellar masses above log M*~10.5MSUN and have ongoing star formation, <SFR>~100 MSUN/yr

granada, may 27ththe x-ray universe 2008 x-ray selected type-2 qsos: high luminosity in heavily...

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