What determines the gas content of galaxies?

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

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

The “new” consensus 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

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?

How do galaxies get their gas? 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?

What cooling+feedback need to do! dark matter mass function (fixed M/L) feedback has successfully depressed galaxy formation in small haloes 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 NB: exacerbated by the high value of WMAP Ω b Benson et al 2003; Keres et al 2009 Formation of faint galaxies supressed by Sne energy

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

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

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

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

Evolution of star formation rates - just cosmology?

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

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

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

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

BCG Star Formation Rate 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 Too many stars! Gas Expelled from system Default Sne feedback no feedback

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?

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?

HST ACS BVI composite 3” NICMOS JH Franx et al NIFS OII white light image SFR OII ~ 42+/-8M o /yr M * ~ 2+/-1x10 9 M o M Dyn ~ 3+/-1x10 9 M o M * /SFR ~ 42Myr v outflow ~ 150km/s t outflow ~ 10Myr OII Ly a SiII