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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 superwinds? • 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 Formation of faint need to do! galaxies supressed by Sne energy feedback has successfully depressed galaxy formation in small haloes The same problem is seen in simulations: Balogh et al., 2001; Springel & Hernquist 2003 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) Benson et al 2003; Keres et al 2009 What cooling+feedback Formation of faint need to do! galaxies supressed by Sne energy feedback has successfully depressed galaxy formation in small haloes The same problem is seen in simulations: Balogh et al., 2001; Springel & Hernquist 2003 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) Benson et al 2003; Keres et al 2009 Fountains or SuperWinds? MW galaxy 0.2~0.1 Dwarf 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 – Galaxies are self regulated (which why we stand a chance!) • 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=0.9 QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture. Z=0.1 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 Default Sne feedback “star formation efficiency puzzle” But where does the low entropy gas go? Data: Lin etal 2003 No feedback Too many stars! default High energy winds AGN driven winds McCarthy et al., 2009 Gas Expelled from system no feedback BCG Star Formation Rate “the cooling flow crisis” Voit & Bryan process seems to work! But where does the low entropy gas go? Default Sne feedback No feedback Too many stars! default High energy winds Gas Expelled AGN driven winds from system 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? Franx et al. 1999 Lya OII HST ACS BVI composite SiII SFROII ~ 42+/-8Mo/yr M* ~ 2+/-1x109Mo MDyn ~ 3+/-1x109Mo M*/SFR ~ 42Myr voutflow ~ 150km/s toutflow ~ 10Myr NIFS OII white light image NICMOS JH 3”