SDSS :
Why do galaxies cluster?
initial fluctuations in early universe
gravity
cosmology
physics: galaxy formation
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Why high redshift?
time leverage
earlier phase of galaxy evolution
additional constraint on models

DEEP2: A Redshift Survey at z=1
Collaboration b/w UC-Berkeley and UC-Santa Cruz using the DEIMOS spectrograph on the Keck II telescope to study both galaxy properties and largescale structure at z=1.
Observational details:
• 3 sq. degrees
• 4 fields on sky
• primary z~0.7-1.4
• ~7-9 Gyr ago
•
40k redshifts
• ~5·10 6 h -3 Mpc 3
•
80 Keck nights - 3 years
• One-hour exposures
•
R
AB
=24.1
• high resolution - robust z’s

DEEP2 Redshift Survey: z=0.7-1.3
Cone diagram of 1/12 of the full DEEP2 sample

Quantify clustering:
probability of two galaxies separated by r
relative to a random unclustered distribution
large on small scales, small on large scales r
0 x
(r) follows a ~power-law prescription locally: x
(r) = (r
0
/r) g with r
0
~5 Mpc/h and g
~1.8
= scale where the prob. of a galaxy pair is 2x random larger r
0
= more clustered

Trace different physics on different scales:
- small scales (r < 100 kpc/h): mergers + galaxy-galaxy interactions
- intermediate scales (100 kpc/h < r < 2 Mpc/h): radial profiles of galaxies w/in halos / clusters
- large scales (r > 2 Mpc/h): large-scale density field / cosmology / host dark matter halo mass

star-forming, gas+dust, spiral, ‘late-type’
Red: non-star-forming, little gas/dust, elliptical, ‘early-type’ red sequence
Blanton et al.
2003 blue cloud
Bi-modal color distribution magnitude

Willmer et al. 2006 ApJ / Faber et al. 2006 ApJ

Galaxy Clustering as a Function of Color
Red
Red galaxies are more clustered and have larger velocity dispersion/fingers of god: reside in overdense environments + groups.
Detect coherent infall on large scales for blue and red galaxies.
First time this has been seen at z=1! Need precise z’s.

Galaxy Clustering as a Function of Color green
Color-density relation strongly in place at z=1.
No color dependence w/in red sequence, but there is w/in blue cloud. Green galaxies as clustered as red.
blue red red: blue:
(for M
B
<-20, L>L*, z=0.7-1.0) r r
0
=5.17 (0.26) g
=1.97 (0.04)
0
=3.83 (0.19) g
=1.67 (0.05)
Which galaxies move to the red sequence by z=0?
Redder of the blue cloud + green galaxies.
Coil et al. in prep

Galaxy Clustering as a Function of Color
Quantify minimum dark matter halos mass as a function of galaxy color (for M
B
<-20): red: b=1.6, M halo
>2 10 12 M o
/h blue: b=1.3, M halo
>4 10 11 M o
/h
- important for color bimodality theories and simulations of gas accretion and star formation
Color-density relation is not caused by clusters - very few clusters at z=1. Either caused by groups or intrinsic galaxy or halo property such as age/stellar mass/halo mass.
The ‘green’ population is distinct - as clustered as red galaxies, but kinematics of blue galaxies. Shows infall on large scales likely at the edges of groups/filaments and falling in. Likely a transition population moving to red sequence.
Coil et al. in prep

QSO/AGN may be important in how galaxies evolve:
many/most galaxies have SMBH
m
BH
s bulge relation
simulations: feedback from AGN or SNe is needed to shut off SF and create the color-mag diagram
mergers are needed to create ellipticals - may involve quasars as disk galaxies collide
Can test galaxy and QSO/AGN formation and evolution models with observed clustering

36 SDSS + 16 DEEP2 spectroscopic broad-line
QSOs in the DEEP2 fields between z=0.6-1.4:
DEEP2
SDSS
(near M*)

Cross-correlation of DEEP2 galaxies and SDSS QSOs.
Errors include Poisson errors + cosmic variance.
Similar errors as surveys with
1000s of QSOs (eg. 2dF).
Divide by the clustering of
DEEP2 galaxies around DEEP2 galaxies to get the bias of QSO hosts…
Coil et al. 2007 ApJ

QSO relative bias = 0.9 (0.2)
QSO absolute bias = 1.2 (0.3)
Cluster more like blue galaxies than red! (2 s
) ---not what is found locally at z=0.
Constrains host type for QSOs
(blue) and QSO host halo masses:
Min. halo mass = 5x10 11 M
0
Mean halo mass = 3x10 12 M
0
No dependence is seen on magnitude or redshift.
Coil et al. 2007 ApJ

red color blue
Chandra survey in the
EGS: 200 ks depth
Have ~10,000 galaxies and ~200 (so far) X-ray sources w/ redshifts.
Can measure the crosscorrelation of X-ray AGN with galaxies.
z=0.7-1.4
-16 M
B
Nandra et al. 2006 ApJL
Barger et al. 2003 AJ quasars
-24
X-ray AGN hosts are bright and on red sequence or massive end of blue cloud.
(even the faint ones:
L x
~10 42-44 erg/s, f x
~1.5 x 10 -15 erg/s/cm 2 )

First results:
significant dependence with optical luminosity: brighter AGN
(-20.5>M
B
>-23) are ~50% more biased/clustered than fainter
AGN (-17.5>M
B
>-20.5)
-X-ray AGN cluster more like red than blue galaxies
-cluster more than QSOs!
-redder X-ray AGN cluster more than bluer AGN
-consistent w/ galaxies undergoing a QSO phase before settling on the red sequence w/ an AGN
Coil et al. in prep

Competing QSO/AGN formation and evolution models predict different clustering properties, through assumed accretion and lifetimes:
- all begin with major mergers
Kauffmann and Haenelt 2001 predict a strong luminositydependence to QSO clustering:
assume an exponentially declining light curve, time= t
M_B ~ gas mass accreted / t
gas mass accreted ~ host halo mass
luminosity~halo mass brighter QSOs cluster more

Lidz, Hopkins et al. 2005 predict less luminosity-dependence (but still some), as the light curve is not exponential
- bright and faint QSOs are similar objects in same halos, but in different stages of their evolution - similar clustering
- bias at z~1 is too high (b~2)
- X-ray AGN cluster like quasars
Croton et al. 2006 include a second mode for low-L AGN: if halo M > M threshold then no gas accretion (~5 10 11 M
0
)
- gas is shock heated, shuts off SF, creates color bimodality, shuts off black hole accretion - no QSO - but there is a low-L AGN
- predict blue galaxies have QSOs at z<2 and red galaxies have low-L
AGN - good qualitative agreement with our results!
Clustering of QSOs constrains lifetimes, host halo mass, host galaxy type and differentiates between formation models.

•
Galaxies have a bimodal color distribution at z=1, similar to z=0.
LF studies show that red galaxies have been forming since z=1.
•
Red galaxies are more clustered than blue galaxies at z=1, with a steeper slope and stronger fingers of god.
•
Galaxies that are likely to evolve from blue to red are the reddest of the blue galaxies and green galaxies.
•
Color-density relation is not due to clusters!
•
Galaxies that host QSOs at z=1 reside in the same mass halos as typical DEEP2 galaxies and have blue host galaxies.
•
X ray-selected AGN cluster like red galaxies at z=1 - at later stage in evolution from QSOs?
•
Place strong constraints on QSO/AGN formation models.