AGN feedback and its influence on massive galaxy evolution

Transcription

1 AGN feedback and its influence on massive galaxy evolution Darren Croton (University of California Berkeley) Simon White, Volker Springel, et al. (MPA) DEEP2 & AEGIS collaborations (Berkeley & everywhere else)

2 Outline Large-scale galaxy surveys have provided a new window into the Universe 1. Simple galaxy formation models 2. The mystery of massive galaxies 3. Is environment important?

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4 Properties of galaxies Baldry et al Kauffmann et al What is the origin of this bi-modal behaviour?

5 Properties of galaxies Baldry et al What is the origin of this bi-modal behaviour?

6 Semi-analytic galaxy formation models Semi-analytic models couple the analytic evolution of baryons to the dynamical evolution of a dark matter N-body simulation They provide a theoretical framework within which to explore galaxy formation (White & Frenk 1992, Croton et al. 2006)

7 Semi-analytic galaxy formation models Croton et al gas infall and cooling star formation supernova feedback galaxy mergers and starbursts metal enrichment (black hole growth and AGN) Text The physics we implement is simple, parameterised, and motivated by both theory and observation

8 How gas cools in a dark matter halo Furusho et al Infalling gas (fb) will heat to the virial temperature of the dark matter halo 2. The gas can be modelled as an isothermal sphere (!~1/r 2 ) 3. We can predict the rate at which this gas will cool => Where there s fuel, there s fire (i.e. star formation) (Bertschinger 1989, White & Frenk 1991)

9 Cooling rates in the model vs. observation model data ROSAT clusters (taken from Peres et al. 1998) Cooling rates inside the cooling radius

10 The Millennium Run dark matter simulation dark matter particles 500 Mpc/h box side length mass resolution of 8.6 x 10 8 Msun softening of 5 kpc/h up to ~25 million (sub)structures followed ~7 million galaxies identified at z=0 with L B > 0.1LB *

11 The predicted galaxy population The relationship between galaxy colour and stellar mass Croton et al The mean stellar ages of galaxies as a function of galaxy mass

12 The predicted galaxy population Croton et al The galaxy luminosity function grossly overpredicts the abundance of bright galaxies

13 Failure of the model The L<L* bi-modality is reasonably consistent with the observations due to the satellite/central galaxy distinction Clearly this model fails to produce a L>L * galaxy population like that observed. Why? Perhaps a more efficient mechanism is missing that can totally sweep the cold gas out of the galaxy during a merger? Quasar winds inject large amounts of energy into the IGM... Springel et al have used merger triggered quasar events to grow black holes and blow strong winds

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15 The over-cooling problem However its unlikely that this scenario can work as global mechanism: Quasars are common at high redshift (z~2-3) but not at the present day Halos grow significantly at z<1, thus any gas ejected at high redshift will have been replenished by z=0 De Lucia & Blaizot 2007 Richards et al. 2005

16 The over-cooling problem Locally, in massive clusters we do see substantial hot x-ray halos that should be cooling at their centre The fact that they are not indicates another heating source: low luminosity AGN

17 The AGN radio-mode Heating source that keeps gas out of the central galaxy Motivated by observations in cooling flow clusters Sub-Eddington accretion from hot gas onto black hole Efficient at late times, ongoing heating source ṁ BH 3 m BH V vir L BH = η ṁ BH c 2 black hole accretion rate radio-mode AGN luminosity Croton et al. 2006

18 The effect on cooling rates Suppression of cooling gas cooling flow suppression is most efficient in massive halos at late times

19 z=0 galaxy light

20 New colours and ages of massive galaxies massve galaxies are now red and old, consistent with that observed in the local universe

21 The luminosity function of galaxies The heating source is able to produce the correct knee in the galaxy luminosity function

22 A bi-modal galaxy distribution? spiral blue star-forming! elliptical red dead 1. The hierarchical evolution of dark matter halos provides excessive amounts of baryons at late times that can (presumably) cool on tcool<th 2. Transforming blue, star forming spirals into red and dead ellipticals requires more than just mergers and supernova

23 Is environment important for star formation quenching?

24 The smoothed 2dFGRS density field

25 Galaxy populations vs. environment Croton et al Relative populations: early and late type galaxies 2dFGRS Significant excess of late-type (star forming) galaxies in the voids. Early-type (quiescent) galaxies dominate in the clusters. What processes produce early type galaxies in such under-dense regions of the universe?

26 Theoretical predictions The Millennium Run semi-analytic galaxy formation model The model predicts that there should be a population of red earlytype galaxies in void regions of the universe Croton & Farrar (in prep.)

27 So what is special about void earlytype galaxies? Msun Msun Msun Croton & Farrar (in prep.) SFR vs. redshift in DM halos of fixed final mass

28 So what is special about void earlytype galaxies? Msun Msun Msun Croton & Farrar (in prep.) dashed=cluster solid=mean dotted=void SFR vs. redshift in DM halos of fixed final mass

29 So what is special about void earlytype galaxies? Croton & Farrar (in prep.) Halo mass function in different environments

30 Summary Can we understand massive galaxy formation in a LCDM universe? Quasar winds may shape the properties of high redshift galaxies, but at z<1 they are unlikely to significantly account for the observed properties. A heating source in the form of a low luminosity AGN, feed from the hot halo, is an energetically feasible solution that can dramatically alter the properties of massive galaxy evolution. Galaxies appear to only know about their large-scale environment through their DM halo. Everything I have shown today is publicly available: The full Millennium Run galaxy + halo catalogues (~25 million galaxies/halos, 0<z<127) are now available through the GAVO SQL interface for use by the community see astroph/