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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