1. Clustering properties and environment of AGN
R. Gilli,
T. Miyaji, J. Silverman, G. Zamorani
and many others (mainly from the COSMOS collaboration)

2. A few issues and questions
Where do AGN live?
(host galaxies, enviroment, dark matter halos)
Does environment play a role in triggering an AGN?
Mergers, galaxy interactions or internal secular processes?
From AGN clustering:
Duty cycle and lifetime
Descendants and progenitors
L/LEDD distribution
Towards an evolutionary sequence

3. Clustering = spatial distribution
The correlation function – w(θ), ξ(r), wp(rp) - is a statistical
description of a spatial distribution: it simply measures how
many pairs of objects are found over a random distribution

4. Random distribution

5. Highly clustered distribution

6. Clustering of dark matter and halos
z=3.0
z=0.0
ξ(r)
r [Mpc]
z=0.0
z=3.0
Millennium simulation (Springel+05)
Moustakas & Somerville 04
Halos form in high
density peaks;
at each redshift more
massive halos are
more clustered

7. Infos from AGN clustering
Correlation length r0 ≈
powerlaw normalization
On small scales (< 1-2 Mpc): objects
in the same dark matter halo
(1-halo term).
Infos on the mechanisms triggering
nuclear activity: mergers, fly by or
secular processes?
On large scales (>1-2 Mpc): objects in
different halos (2-halo term).
Infos on location of AGN within the
cosmic web;
hosting dark matter halos and
galaxies; typical environment
From 2dF

8. Host galaxies and dark matter halos at z~1
r0 (z~1) = Mpc/h
Minimum halo mass:
logM > Msun/h
AGN at z~1 seem to
be preferentially
hosted by massive
galaxies (M*> Msun)
Consistent with non-clustering studies
(eg. Silverman +09)

9. AGN lifetime from clustering
tA nA
tH nH =
Optical QSOs (logLbol~46.5 , z~1-2): tA ~ Myr
X-ray AGN (logLbol~45.5 , z~1): tA ~ 1 Gyr

10. Clustering as a function of redshift
Despite earlier claims, X-ray AGN
cluster similarly to optically
selected QSOs at the same redshifts
Radio-galaxies, instead are more
clustered.
Halo mass, logM/Mo~ ,
typical of poor groups,
seems the be the same at any
epoch: is there any halo threshold
mass for nuclear triggering??
CDFS
Millennium halos

11. The Hickox et al. (2009) cartoon
Threshold halo mass (group mass) to start the sequence through galaxy
mergers

12. Descendants of z~0.7 X-ray AGN
Red, early
green, transitional
blue, late
Loh+10, GALEX
X-ray AGN
conserving scenario (Nusser & Davis 94, Moscardini +98): objects in halos with a
given mass simply evolve without merging along the density field
X-ray AGN at z~0.7 will switch off by z=0 and their relic SMBHs will be hosted
by local bright (L~L*) early type galaxies

13. So mergers are the triggering mechanism?
Hopkins+08
z<0.4
1-halo term
QSOs are consistent with being triggered by mergers, Seyferts probably not
Issue still to be solved..