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What determines the gas content of galaxies?

Delve into the puzzle of galaxy formation and the key elements influencing gas content, such as hot and cold fractions, wind loading, AGN feedback, and star formation efficiency. Explore the role of baryons in galaxies and the challenges in understanding gas dynamics.

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What determines the gas content of galaxies?

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  1. What determines the gas content of galaxies?

  2. Galaxy formation - a reminder of the puzzle • The fraction of baryons that are “cold” (stars+cold gas) is small. • ~10% overall. • Rising to 25% in MW haloes. Guo et al 2010; Trujillo-Gomez et al 2010

  3. Galaxies are part of the bigger picture • In groups we can make a complete baryon census • The cold fraction is ~10% • Hot gas is ~20% in groups rising to 70% in clusters McCarthy et al 2009

  4. The supply of new gas is limited by halo growth. Galaxies recycle their gas into the halo many times. Wind loading suppresses the formation of dwarf galaxies. Winds and recycling timescale determine galaxy formation efficiency, not star formation. At high masses, the gas supply is shut off. things you have to give up! The supply of gas is limited by cooling Galaxies accrete their gas and slowly consume it. Star formation efficiency needs to be understood The “new” consensus

  5. Some Questions • How do galaxies get their gas? • What determines the balance of inflow and outflow? • Where are the baryons in galaxies? • Are galaxies part of a bigger picture?

  6. Hot accretion aka “cooling flows” Not relevant when we talk about real galaxies. Shutdown with AGN feedback? rapid accretion aka “cold flows” Flows that never heat up? So what? Reionisation Not part of today’s story. Recycled gas Need to get the velocity and mass loading right! Fixed wind speed destroys L* galaxies SA models need  ~ v-2 to v-3 Galactic fountains or super-winds? Is there any evidence for high mass loading? Reheated gas cools again - or does it? High velocity clouds? Hot gas in groups and galaxy haloes? DLA abundance? How do galaxies get their gas?

  7. What cooling+feedback need to do! Formation of faint galaxies supressed by Sne energy feedback has successfully depressed galaxy formation in small haloes dark matter mass function (fixed M/L) NB: exacerbated by the high value of WMAP Ωb but cooling is now too effective in high mass haloes (there's more gas left over) The same problem is seen in simulations: Balogh et al., 2001; Springel & Hernquist 2003 Benson et al 2003; Keres et al 2009

  8. What cooling+feedback need to do! Formation of faint galaxies supressed by Sne energy feedback has successfully depressed galaxy formation in small haloes GIMIC simulation (Crain et al 2010) dark matter mass function (fixed M/L) NB: exacerbated by the high value of WMAP Ωb but cooling is now too effective in high mass haloes (there's more gas left over) The same problem is seen in simulations: Balogh et al., 2001; Springel & Hernquist 2003 Benson et al 2003; Keres et al 2009

  9. Fountains or SuperWinds? Schaye & Dalla Vecchia 2008, Mitchel et al 2010 MW galaxy 0.2~0.1 Dwarf galaxy 0.2~1

  10. Where are the Baryons? How did they get there? Bower et al 2008 McCarthy et al 2010

  11. What determines the balance of inflow and outflow? • Star formation efficiency • Probably the least important (which why we stand a chance!) • Galaxies are self regulated • Evolution of SSFR • The end of down-sizing • Supernova “Feedback” • Wind loading and energetics • Galactic fountains vs superwinds

  12. Evolution of star formation rates - just cosmology?

  13. The end of “Down-Sizing”? Z=0.9 Z=0.1 Roles+DEEP2 (Gilbank et al 2010) Factor 3.5+ increase in normalisation, but no change of shape. No “down-sizing”!

  14. What form is the gas? • “sub-grid” models vs molecular cooling • The role of pressure • The role of the Toomre criterion? • Predicting observations

  15. A bigger picture? • Galaxy haloes are not “closed boxes” • Most of the baryons are missing • How and why?

  16. Cooled Gas Mass Default Sne feedback • “star formation efficiency puzzle” • But where does the low entropy gas go? • No feedback • default • High energy winds • AGN driven winds no feedback Data: Lin etal 2003 Too many stars! Gas Expelled from system McCarthy et al., 2009

  17. BCG Star Formation Rate • “the cooling flow crisis” • Voit & Bryan process seems to work! • But where does the low entropy gas go? • No feedback • default • High energy winds • AGN driven winds Default Sne feedback no feedback Too many stars! Gas Expelled from system

  18. But… • No evidence for cold flows. • Why do you believe outflows? Even M82 only ~ SFR. • What is the mass budget of galaxies? How many baryons are there in the MW’s halo?

  19. And… • Clusters. 80% why not more. • Triggered star formation in jets? • IMF varied. Why? Submm? Obscurred? • Alpha-enhanced. Why? • How do these winds get out. • Measure 300 km/s blueshift. Grav lens? • Environment. Solved?

  20. Franx et al. 1999 Lya OII SiII SFROII ~ 42+/-8Mo/yr M* ~ 2+/-1x109Mo MDyn ~ 3+/-1x109Mo M*/SFR ~ 42Myr voutflow ~ 150km/s toutflow ~ 10Myr HST ACS BVI composite NIFS OII white light image 3” NICMOS JH

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