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Feedback, Models and the effect of Environment Richard Bower & the GALFORM team Andrew Benson, Andreea Font, Ian McCarthy, Rowena Malbon, John Helly, Carlos Frenk, Carlton Baugh, Shaun Cole, Cedric Lacey….
Old stuff! Quick overview of the “new” Durham models - AGN feedback and what it does for you. New stuff! Galaxy Ecology - modeling how galaxies interact with their environment The flip-side of galaxy formation - the thermal history of the IGM/ICM What I want to say!
The three problems of galaxy formation • The bright end of the luminosity function • What sets the break in the galaxy luminosity function? • The “cooling flow” problem • Why don’t cooling flows result in bright blue galaxies at the centres of clusters? • The “hierarchy” problem • Why are the brightest galaxies old and red? These problems are closely interconnected: do AGN provide the solution? 4. Only 10% of the baryons form into stars!!! Where are the other baryons? what are their properties?
What cooling+feedback need to do! 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
The Power of AGN Comparison of energies: Total thermal energy of a 1013 Mo halo … 1061 erg Accretion energy of a 109 Mo black hole … 2 x 1062 erg It seems unlikely that AGN are unimportant!
The two forms of AGN feedback “Quasar” mode (eg. Granato et al., 2004, Springel et al 2005) “Radio” mode feedback (eg. Croton et al 2006, Bower et al 2006 Okamoto et al 2007) Radio Temperature X-rays Shock heating Uplifting matterial? Mixed plasma and ICM? M87: Forman et al 2006; Perseus: Fabian et al 2000, 2006 Springel et al 2005
The AGN feedback loop AGN fuelling Cooling “radio” mode Hydrostatic ? tcool>tfree-fall Keres et al 2005; Dekel & Birnboim 2003; Binney 2004
Present-day Galaxies No AGN • Bj and K luminosity functions • Switching “radio” feedback off leads to a population of very bright galaxies formed in cooling flows • But position of the LF break is set by the division between rapid and hydrostatic cooling haloes. Bj band dust No dust No AGN K-band
Evolution of the Stellar Mass Function • The evolution of the stellar mass function from Drory et al 2005. • More recent tests now possible (eg Van Dokkum et al 2007, Bundy/Stringer 2008) z=0 AGN model McClure et al 2006 Integrated SMD agrees with Stark et al 2006
Evolution of colours • Evolution of red sequence tracks passive evolution • …but the blue sequence also get bluer – matches the increase in SFR density Bower et al 2006 & De Lucia et al 2006 galaxy catalogues are public! www.mpa-garching.mpg.de and www.icc.dur.ac.uk
Summary (of part I) • AGN + semi-analytic galaxy formation provides a frame work for understanding the “anti-hierarchical” universe • B06 is by no means the only model to use AGN: eg., Hatton et al 2003, Granato et al ‘04, Croton et al. ‘06, De Lucia et al ‘07, Menci et al ‘07, Cattaneo ‘07, Summerville ‘08 - but be aware of the different flavours. • The model seems to do reasonably well …. (I’m sure someone will contradict me!)
But models that work are boring… Part II:Improving the model A better description of environmental processes (Pre-) heating the IGM
Problems with the standard model… (one of them) • Satellites are too red. Regardless of halo mass. • The effect of “strangulation” is overestimated • A satellite galaxy orbiting within another halo is assume to loose its own hot gas reservoir. • This is far too simplistic Weinmann et al 2006; Baldry et al 2006.
Environmental Physics is not correctly handled Satellite Galaxies All Galaxies All satellites are red! No blue satellites!
Environmental Physics is not correctly handled • Old Strangulation model • Remove gas reservoir as galaxy orbits larger halo Larson, Tinsley & Caldwell 1980 McCarthy et al – an improved model for halo stripping – depends on the orbit of the satellite and the gas content of the satellite and main halo. (Actually, Gunn & Gott’s formulae re-calibrated for halo gas using numerical simulations) Hot gas reservoir • Is this realistic? • Mass ratio of haloes • Gas atmosphere of the main halo SNe winds quickly exhaust disk gas Strangulation = suffocation = starvation
Controlled SPH and FLASH simulations McCarthy et al. 2007
Solving the problem by adjusting the environment physics • Dramatic improvement in the environmental dependence of satellite properties from reducing the effects of starvation. Font et al 2008
Problem solved? There are many more tests of the interaction of galaxies with their environment - more work is needed to extract the data and model in comparable ways (Balogh/Font/McGee/IGM/RGB et al 2008)
A closer look at the colour distribution of galaxies The Field The Clusters Too many intermediate colours galaxies, not enoough blue objects Too many faint red galaxies (Distributions shifted to to agree with red-sequence colours) Font, Balogh, McGee et al, in prep.
What about the ICM? The flip-side of galaxy formation Only 10% of the baryons form into stars!!! - what about the rest of the baryons???
X-ray Emission from Groups and Clusters • L-T relation : well known that the self-similar relation fails • AGN: standard model just prevents cooling… it doesn’t affect the X-ray luminosity B06 Model Data from Horner et al. Data from Osmond & Ponman
The AGN feedback loop (new version) • A note for pundits: • This is “in-situ” heating • there’s no “pre-heating” • its going to be expensive, but not prohibitively so. AGN fuelling Cooling “radio” mode P=min(Ledd,Mcool) Hydrostatic ? Heating redistribute halo gas Based on the “excess energy” method (Wu et al 1999), plus the hydrostatic criterion
X-ray Emission from Groups and Clusters • L-T relation : well known that the self-similar relation fails • AGN: standard model just prevents cooling • Revised model, AGN feedback redistributes halo gas until the cooling rate drops and AGN power is cut off AGN redistributes halo gas A huge step forward - I’ve been trying to achieve this for ten years! Scatter driven by diverse assembly history Voit & Bryan 2001; Bower et al 2008, MN, in press (astro-ph/0808.2994)
The baryon content of haloes - where are all those baryons? “Ejected” gas T (keV) Hot X-ray emitting gas Stars and cold gas
AGN regulate the formation of the brightest galaxies. The break in the LF is set by hydrostatic vs rapid cooling. The model describes the properties of field galaxies and their evolution well. Cluster galaxies form earlier than field galaxies But… Galaxy ecology is a formidable test Improved treatment of ram-pressure stripping of halo gas makes a huge improvement Font et al 2008 X-ray emission from groups and clusters Over estimated in standard model AGN do more than prevent cooling Bower et al 2008 Conclusions – what you should remember!
Evolution of the Stellar Mass Function • The evolution of the stellar mass function from Drory et al 2005. z=0 AGN model McClure et al 2006 Integrated SMD agrees with Stark et al 2006