cool halo gas in a cosmological context kyle stewart “team irvine” uc santa cruz galaxy...
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Cool Halo Gas in a Cosmological Context
Kyle Stewart“Team Irvine”
UC Santa Cruz Galaxy Formation Workshop
8-20-09
Kyle Stewart“Team Irvine”
UC Santa Cruz Galaxy Formation Workshop
8-20-09
Collaborators:James Bullock, Betsy Barton (UCI) Tobias Kaufman, Lucio Mayer (UZH) Jürg Diemand, Piero Madau (UCSC) James Wadsley (McMaster), Ari Maller (NYCCT)
Outline
• Theoretical Motivations– Baryonic content of DM halos– Gas accretion via gas-rich mergers
• Observing Cool Halo Gas– Unresolved / open questions
• The Simulation: VL2 + GASOLINE– Covering Fraction – Kinematics: Halo Gas vs. Galaxy
Motivations
• How do galaxies acquire their cool gas?– Cold flows? Cloud Fragmentation? (e.g. Keres
et al. ‘09, Dekel & Birnboim ‘06, Maller & Bullock ’04, most of Tuesday’s talks…)
• Gas rich mergers?– Stewart et al. 09
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Small halos have a lot of gas and few stars (especially at z~1)
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Stewart 2009Abundance matching (Conroy & Wechsler ‘09)
+ baryonic TF
Gas-rich mergers & galaxy assembly
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Stewart et al. 2009
~30% of an L* galaxy’s baryons accreted in Major, gas-rich mergers over it’s history (since z=2).
~20% of bright galaxies at z~1 have had a Major, gas-rich merger in last Gyr(not based on this plot)
Motivations
• How do galaxy acquire their cool gas?
• How can we test ideas?
• Absorption-systems as probes of cool halo gas…
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Observing Gas Around Galaxies:
QSO (Mg II)
D ~ 100 kpc
(or less)Image from
Tripp & Bowen (2005)
1) Covering Fraction
2) Cloud vs. Galaxy Kinematics
Observing Gas Around Galaxies:
1)Covering Fraction2) Cloud vs. Galaxy KinematicsBut what ARE they?
Spherical halo gas?Cold Filaments? Pressure-confined gas clouds?Outflowing winds? Tidal Streams?
Mg II Cf ~20-80%
e.g. Tripp & Bowen ’05;
Tinker & Chen ‘08; Kackprzak et al. '08
Observing Gas Around Galaxies:
1)Covering Fraction2) Cloud vs. Galaxy Kinematics
Kacprzak et al. ‘09 (submitted)
7/10 Mg II absorbers show velocities that co-rotate with galaxy
Galaxies Probing Galaxies
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z~0.5
z~0.7
Rubin et al. ‘09
Keck/LRIS absorption spectrum
Cool gas ejected from host galaxy during past merger?
Spatially-extended complex of cool clouds at d>17kpc from galaxy (with high velocity width)
Our Simulation:
VL2 (initial conditions)
+
GASOLINE (sph code)
Die
mand e
t al. ‘
08
Wadsl
ey e
t al. ‘
04
Some stats:WMAP3 cosmo: =0.24, =0.76, h=0.73, σ8=0.77, b=0.042mDM, mgas, mstar ~3e5, 4e5, 1e5 Msun,
Np~4 million. Sph smooth len: 332 pc. Final halo mass Mvir~2.e12 Msun
‘Blast-wave’ feedback of Stinson et al. ‘06; Haardt & Madau ‘96 UV field; NOTE: no strong blow-out winds
Log HI [Msun/pc3 ]= [-8, -1]
Log stars [Msun/pc3 ] = [-7, 1]
Results: Covering Fraction
Router ~ 50 kpc (comoving)
Ngrid ~ 1000
Rinner ~ 5 kpc (comoving)
LOS “covered” if N(HI)
>1016,18,20
atoms/cm2
Results: Covering Fraction
Note: VL2 chosen to be quiescent at late
times
Fragmented Flows + Mergers
Cold flows(and mergers)
(averaged over 3 projections)
Covering Fractio
n Depends on
Recent Gas A
ccretion!
Gas and Galaxy Kinematics:
Log HI = [-7, 1] LOS velocity
[-250 to +250 km/s]
Gas and Galaxy Kinematics:
Log HI = [-7, 1] LOS velocity
[-250 to +250 km/s]
Summary:• High-res SPH simulation of VL2 halo with gas + stars
• Extended cool halo gas betrays a complex assembly history:– Gas-rich & star-poor mergers are common and responsible for much
of the halo gas (especially at z<2)
– These mergers would be invisible to pair-counts at fixed luminosity
• Cool halo gas tends to co-rotate with the galaxy, as indicated by observations. This gas includes clouds, streams, and other complex structures – the gas that will build the galaxy itself.
• Covering Fraction for cool gas depends on recent gas accretion: smooth (or fragmented) filaments, mergers, etc.
• Covering fraction in VL2 remains high well past the time associated with the canonical cold flow epoch, as a result of mergers and infalling fragments.
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Extra Slides:
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