1. 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….

2. What I want to say! Old stuff! New 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

3. 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?

4. 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

5. AGN the new ingredient

6. The Power of AGN Comparison of energies:
Total thermal energy of a 1013 Mo halo … erg
Accretion energy of a 109 Mo black hole
… 2 x 1062 erg
It seems unlikely that AGN are unimportant!

7. 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
X-rays
Temperature
Shock heating
Uplifting matterial?
Mixed plasma and ICM?
M87: Forman et al 2006; Perseus: Fabian et al 2000, 2006
Springel et al 2005

8. The AGN feedback loop AGN fuelling Cooling “radio” mode Hydrostatic ?
tcool>tfree-fall
Keres et al 2005; Dekel & Birnboim 2003; Binney 2004

9. Present-day Galaxies Bj and K luminosity functions
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

10. 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

11. 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!
and

12. 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!)

13. Part II: Improving the model
But models that work are boring…
Part II: Improving the model
A better description of environmental processes
(Pre-) heating the IGM

14. 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.

15. Environmental Physics is not correctly handled
Satellite Galaxies
All Galaxies
All satellites are red!
No blue satellites!

16. 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

17. Controlled SPH and FLASH simulations
McCarthy et al

18. 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

19. 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)

20. 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.

21. The flip-side of galaxy formation
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???

22. 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

23. 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

24. 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/ )

25. The baryon content of haloes - where are all those baryons?
“Ejected” gas
T (keV)
Hot X-ray emitting gas
Stars and cold gas

26. Conclusions – what you should remember!
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

27. Thank you!

28. 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