gas in the local group james binney & filippo fraternali oxford university
TRANSCRIPT
Gas in the Local Group
James Binney & Filippo Fraternali
Oxford University
Outline
• Missing baryons
• Infall and HVCs
• Extraplanar gas in external galaxies
• The hot halo
• Conclusions
Missing baryons
• Negative vlos of M31 ) MLG=4.8£1012M¯ (Kahn & Woltjer 59 ff)
• b/m=0.17 (Spergel et al 03)
• If MM31'1.5MMW (cf Wilkinson & Evans 99)
• But LV(MW) ' 1.5£1010L¯, so M* ' 3-5£1010M¯
• Implies most baryons missing• Klypin, Zhao & Somerville (02) have MMW=1012M¯
and half baryons missing
Still infalling?
• Muller Oort & Raimond (63) found HI at highly anomalous velocities
• HVCs mapped at ever higher sensitivity ! Leiden-Dwingeloo (Hartman & Burton 1997) & HIPASS (Barnes et al 01) surveys
• Are HVCs distant & massive? (Oort 70; Blitz et al 99)
• Efforts to detect massive extragalactic clouds in other groups repeatedly failed (Pisano & Wilcots 03)
• Clouds usually have detectable H emission (Tufte et al 02; Putman et al 03)
Extraplanar gas
• Some HVCs associated with LG galaxies (Magellanic Stream; Andromeda clouds)
• Most are within MW and of low mass (Westmeier 03)
• Extend to N<1019 cm-2 at which HI hard to detect (Hoffman et al 04; Richter et al 05)
• Significant covering factor
• Have complex shapes (Richter et al 05)
• Local clouds show net infall v ' 50 km/s (de Heij et al 02; Wakker 04)
Outside view
• Counterparts of HVCs now studied in external galaxies
• (M101: van der Hulst & Sancisi; NGC 5668: Schulman et al 94-6; NGC 891, NGC 2403: Swaters et al 97 ! Fraternali, Oosterloo & Sancisi 04)
Extra-planar gas in NGC 891
• Sancisi & Allen 1979 NH ≈ 5 1020 cm-2
• Swaters et al. 1997 NH ≈ 7 1019 cm-2
• Oosterloo et al. 2005 NH ≈ 1.7 1019 cm-2
• Sancisi & Allen 1979 NH ≈ 5 1020 cm-2
• Swaters et al. 1997 NH ≈ 7 1019 cm-2
• Oosterloo et al. 2005 NH ≈ 1.7 1019 cm-2
• Sancisi & Allen 1979 NH ≈ 5 1020 cm-2
• Swaters et al. 1997 NH ≈ 7 1019 cm-2
• Oosterloo et al. 2005 NH ≈ 1.7 1019 cm-2
NGC891: Low rotation of extra-planar gas
Fraternali 2005
vrot~15 km s-1 kpc-1
NGC 2403
.Distance: 3 Mpc
.Type: Sc
.Inclination ~ 62
.Non-interacting
.Very similar to M33
NGC2403: Extra-planar gas
Extra-planar gas
130 km/s
Forbidden gas
Fraternali, Oosterloo, Sancisi, van Moorsel 2001
Thin disc model
NGC2403: Non circular motions
Thin disc Extra-planar gas
V
Lagging haloThin disc
Non-circular motions
purerotation
pure radialinflow
rotation + outflowrotation + inflow
NGC 6946: Extra-planar gas and SF
Boomsma PhD 2005
WRST
Summary (observations) Extra-planar detected up to 15 kpc from plane
Rotation lower than the disc
High velocities (100-200 km s-1)
Global inflow motion
Link with star formation?
Evidence for accretion?
Fountain model(Shapiro & Field, ApJ 1976; Bregman, ApJ 1980)
• Clouds ejected from circular orbits with distributions in v,
• Axisymmetry exploited to build pseudo-data cube
New work (Fraternali & B 05):
• Clouds move ballistically as in Collins, Benjamin & Rand, A&A 02, but may not be visible until zmax or rmax
• Clouds return to disk on first or second passage through z=0• <4% of SN energy needed
Model constraint: vertical distribution
Vkick ~ 75 km s-1
Mhalo ~2 109 M
NGC 891: Lack of low angular momentum
Fast rotating gas
NEED FOR LOW ANGULAR MOMENTUM MATERIAL
NGC2403: lagging gas
Thin disc
Thick disc
60o
Vkick ~ 70 km s-1
Mhalo ~ 5 108 M
NGC2403: inflow/outflowThin disc gas
Extra-planar gas
Radial outflow
NEED FOR INFALLING MATERIAL
V
VR
Vz
Second-passage models
V
VR
Vz
V
VR
Vz
Phase-change models
NGC 2403
NGC 891 Fast rotating gas
Inside view
Summary (models) Models reproduce the vertical extent with reasonable energy
input (<4 % SN energy)
Failure in NGC2403: lack of inflowNeed for accretion
Failure in NGC891: lack of low angular momentumNeed for drag
Seen from inside, a successful cloud model would look like HVC population
But must reverse outflow and diminish rotation
The WHIM
CDM simulations without feedback suffer from “overcooling”
• Natural solution: fast mass loss during GF
• Direct evidence from Moutflow' MSF (Pettini et al 01; Steidel et al 04)
• Also manifest connection of outflow to HVCs (NGC 6946 and …)
• So expect accumulation of gas @
NGC 253 Boomsma et al 05
The hot halo
• Munch (52) detected Ca II and Na I interstellar lines at |v-vLSR|>20 km/s even at high b
• Spitzer (56) argued that cold absorbing clouds must be confined by pressure p/kB'104 K cm-3 of gas with T' Tvir
• At Tvir, Mgas= 0.52£109 (Rmax/R0) M¯
• So CDM requires M>1011M¯ halo to extend to Rmax'1Mpc
• Copernicus, HST and FUSE detect absorption in C IV, O VI, etc
• O VI important because ionize E(O V)=114eV; O VI emission peaks @ T = 3£105 K
HI emission & O VI absorption
• Consistent with O VI at interface of HI and WHIM• Possible evidence that O VI expanding relative to HI
Sembach et al 02
Interaction of HVCs with WHIM
• Density contrast Tvir/THI' 100-104
• Analogous to a transonic sprinkler• Ram-pressure drag (Benjamin & Danly 97)
• = 21 N19/(n-3v200) Myr• Tflight ' 100 Myr• Drag important
Evidence for drag
• Structure of leading arm of Magellanic stream
• Head-tail structure of HVCs (Bruns et al 01)
• Z < Z¯ for complex C
HVCCHVCsPutman et al 03
Problems
• Fountain circulates large mass through extraplanar gas: MHI ' 5£108 M¯ every 100 Myr
• If ejected gas loses 10% of its angular momentum, halo will become corotating if not extensive (Mgas= 5£108 (Rmax/R0) M¯)
• Naively expect moving clouds to be ablated
• Net inflow and low Z (10% Zsun) imply condensation prevails
Conclusions• CDM predicts that most baryons are hidden• Observations of external groups & galaxies
show that HVCs lie at 10 – 100 kpc distances• HVCs are generated by star formation• The basic fountain model does not reproduce:
lag in rotation & net infall• Much evidence for interaction of HI with WHIM• Likely that lag & infall result from interaction with
WHIM• LCDM predicts that WHIM contains bulk of LG
baryons & extends to > 1Mpc