Transcript Slide 1

Cool Halo Gas in a Cosmological Context
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
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Theoretical Motivations
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Baryonic content of DM halos
Gas accretion via gas-rich mergers
Observing Cool Halo Gas
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Unresolved / open questions
The Simulation: VL2 + GASOLINE
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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)
Stewart 2009
Abundance matching (Conroy & Wechsler ‘09)
+ baryonic TF
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Stewart et al. 2009
Gas-rich mergers & galaxy assembly
~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)
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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)
1) Covering Fraction
Image from
Tripp & Bowen (2005)
2) Cloud vs. Galaxy
Kinematics
Observing Gas Around Galaxies:
1) Covering Fraction
2) Cloud vs. Galaxy
Kinematics
But 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 Fraction
2) Cloud vs. Galaxy
Kinematics
Kacprzak et al. ‘09
(submitted)
7/10 Mg II absorbers
show velocities that
co-rotate with galaxy
Galaxies Probing Galaxies
Rubin et al. ‘09
z~0.5
z~0.7
Keck/LRIS
absorption spectrum
Spatially-extended complex of cool clouds at d>17kpc from
galaxy (with high velocity width)
Cool gas ejected from host galaxy during past merger?
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Log rHI [Msun/pc3 ]= [-8, -1]
+
VL2 (initial conditions)
Wadsley et al. ‘04
Diemand et al. ‘08
Our Simulation:
GASOLINE (sph code)
Some stats:
WMAP3 cosmo: W0=0.24, L=0.76, h=0.73, σ8=0.77, Wb=0.042
mDM, mgas, mstar ~3e5, 4e5, 1e5 Msun,
Np~4 million. Sph smooth len: 332 pc. Final halo mass Mvir~2.e12
Msun
3
rstars
=field;
[-7,
sun/pc
‘Blast-wave’ feedback of Stinson Log
et al. ‘06;
Haardt[M
& Madau
‘96 ]UV
NOTE: no strong blow-out winds
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
(averaged over 3 projections)
Cold flows
(and mergers)
Fragmented Flows
+ Mergers
Note: VL2 chosen to be
quiescent at late times
Gas and Galaxy Kinematics:
Log rHI = [-7, 1]
LOS velocity
[-250 to +250 km/s]
Gas and Galaxy Kinematics:
Log rHI = [-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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