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Cool Halo Gas in a Cosmological Context

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).

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Cool Halo Gas in a Cosmological Context

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  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)

  2. 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

  3. 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

  4. Small halos have a lot of gas and few stars (especially at z~1) Stewart 2009 Abundance matching (Conroy & Wechsler ‘09) + baryonic TF

  5. Gas-rich mergers & galaxy assembly 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)

  6. Motivations • How do galaxy acquire their cool gas? • How can we test ideas? • Absorption-systems as probes of cool halo gas…

  7. Observing Gas Around Galaxies: QSO (Mg II) D ~ 100 kpc (or less) Image from Tripp & Bowen (2005) 2) Cloud vs. Galaxy Kinematics • Covering Fraction

  8. Observing Gas Around Galaxies: • Covering Fraction Mg II Cf ~20-80% 2) Cloud vs. Galaxy Kinematics But what ARE they? Spherical halo gas? Cold Filaments? Pressure-confined gas clouds? Outflowing winds? Tidal Streams? e.g. Tripp & Bowen ’05; Tinker & Chen ‘08; Kackprzak et al. '08

  9. Observing Gas Around Galaxies: Kacprzak et al. ‘09 (submitted) • Covering Fraction 2) Cloud vs. Galaxy Kinematics 7/10 Mg II absorbers show velocities that co-rotate with galaxy

  10. 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?

  11. Our Simulation: Log rHI [Msun/pc3 ]= [-8, -1] + Diemand et al. ‘08 Wadsley et al. ‘04 VL2 (initial conditions) 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 ‘Blast-wave’ feedback of Stinson et al. ‘06; Haardt & Madau ‘96 UV field; NOTE: no strong blow-out winds Log rstars [Msun/pc3 ] = [-7, 1]

  12. Results: Covering Fraction Router ~ 50 kpc (comoving) Ngrid ~ 1000 Rinner ~ 5 kpc (comoving) LOS “covered” if N(HI) >1016,18,20 atoms/cm2

  13. Results: Covering Fraction (averaged over 3 projections) Fragmented Flows + Mergers Covering Fraction Depends on Recent Gas Accretion! Cold flows (and mergers) Note: VL2 chosen to be quiescent at late times

  14. Gas and Galaxy Kinematics: LOS velocity [-250 to +250 km/s] Log rHI = [-7, 1]

  15. Gas and Galaxy Kinematics: LOS velocity [-250 to +250 km/s] Log rHI = [-7, 1]

  16. 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.

  17. Extra Slides:

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