Galaxy Clustering Properties at z=1: Results from the DEEP2
Redshift Survey
Alison CoilSteward Observatory
April 2006
Talk Overview
•DEEP2 Redshift Survey overview•Luminosity-dependence of clustering at z=1•QSO-galaxy clustering
The DEEP2 Collaboration
U.C. BerkeleyM. Davis (PI) M. Davis (PI)
M. Cooper M. Cooper
B. Gerke B. Gerke
R. Yan R. Yan
C. ConroyC. Conroy
Steward Obs. A. Coil
U.C. Santa Cruz S. Faber (Co-PI)
D. Koo
P. Guhathakurta
D. Phillips
K. Noeske
A. Metevier
L. Lin
N. Konidaris
G. Graves
LBNL J. NewmanJ. Newman
Maryland B. Weiner
Virginia R. Schiavon
The DEEP2 Galaxy Redshift Survey, which uses the DEIMOS spectrograph on the Keck II telescope, is studying
both galaxy properties and large-scale structure at z=1.
C. Willmer
Large-Scale Structure in 2dF
220,000 galaxies in 1500 sq. degrees - z=0.1
Comparison with Other Surveys
1.00E+03
1.00E+04
1.00E+05
1.00E+06
1.00E+05 1.00E+06 1.00E+07 1.00E+08
Volume ( h -3 Mpc 3)
Number of Galaxies z~0z~1
DEEP2
SDSS
2dF
CFA+SSRS
LCRS
PSCZ
DEEP2 was designed to have comparable size and density to previous generation local redshift surveys and is
>50 times larger than previous intermediate surveys at z~0.3-1.
DEEP2 has a different geometry than local
surveys: 20x~80x1000 h-3 Mpc3 per field
few x smaller than 2dF~4x larger than 1st
epoch VVDS~2.5x COMBO-17
1.5 x COSMOS
Vital Statistics of DEEP2
• 3 sq. degrees of sky• 4 fields (0.5o x <2o) - lower cosmic variance errors• primary z~0.7-1.4 (pre-selected using BRI photometry)• >40,000 redshifts• comoving volume: ~5·106 h-3 Mpc3
• 400 slitmasks over 80 Keck nights• One-hour exposures• RAB=24.1 limiting magnitude• 1200 l/mm: ~6500-9200 Å• 1.0” slit: FWHM 68 km/s - high-resolution
Coordinated observations ofthe Extended Groth Strip
(EGS)Spitzer MIPS, IRAC
DEEP2 spectra and Caltech / JPL Ks imaging
HST/ACSV,I (Cycle 13)
Background: 2 x 2 degfrom POSS
DEEP2/CFHTB,R,I
GALEX NUV+FUV
Chandra & XMM: Past coverage Awarded (1.4Ms)
Plus VLA (6 & 21 cm), SCUBA, etc….
Redshift Distribution of Data: z~0.7-1.4
Status: -three-year survey-currently ~90% complete-hoping to finish EGS this spring…
Target galaxies to be at z>0.7 with B-R, R-I colors. The cuts are very successful! Only miss 3% of high-z objects (blue). We do not apply z cuts in the EGS!Redshifts are precise (30 km/s) and have high confidence: OII doublet and Ca H+K abs. features
Observing conditions in spring ‘04 were poor…
The CFHT dome as seen from Gemini
Redshift Maps in 4 Fields: z=0.7-1.3
Cone diagram of 1/12 of the full DEEP2 sample
Galaxy Clustering Primer
(r) follows a ~power-law prescription locally:
(r) = (r0/r) with r0~5 Mpc/h and ~1.8
r0 = scale where the prob. of finding a galaxy pair is 2x random
Smallest scales (r < 100 kpc/h): mergers + galaxy-galaxy interactionsIntermediate scales (100 kpc/h < r < 2 Mpc/h): radial profiles of
galaxies w/in groups and clusters Large scales (r > 2 Mpc/h): large-scale density field / cosmology
Locally, both 2dF and SDSS quantify galaxy clustering to few %-can now measure to similar accuracy at z=1
Luminosity-dependence of clusteringat z=1 in DEEP2 data
From a sample of 25,000 redshifts over 3 deg2 in 4 fields -
create volume-limited subsamples as a function of
luminosity.
Brighter samples are more clustered (r0~3.7-4.4 Mpc/h) and have steeper slopes on
small scales -- preferentially found in groups at z=1 -- sub-
structure.
Coil et al. ApJ, astro-ph/0512233100 kpc/h 20 Mpc/h
Galaxy separation(Mpc/h)
wp(
r p) -
clu
ster
ing
ampl
itud
e
Deviations from a power-law at z=1
Similar deviations from a power-law that are seen at z=0.1.Generally interpreted as one-halo and two-halo terms.
Coil et al. 2006, ApJ
SDSS z=0.1 DEEP2 z=1
Measure one-halo and two-halo terms
Coil et al., 2005 ApJ
Can measure the one-halo and two-halo terms directly with a group catalog! Compare with mock catalogs that use an HOD model + DM NFW profile and find a discrepancy on small scales - ?
Data Mock
Bias: galaxy clustering/dark matter clustering
Observations + theory: z=3: b~4 z=0: b~1
Galaxy formation sim. at z=3 by Kauffmann et al. grey=dark matter particles colors=galaxies
Bias is expected to evolve with redshift, as first galaxies at high-z
formed in densest regions.
LBGs SDSS
Evolution of bias and dependence on scale and galaxy
properties places strong constraints on galaxy formation
theories.
Luminosity/scale-dependence of bias
From the observed bias can infer the dark matter halo masses that host these galaxies: M > 9 1011-3 1012 M/h
Have now measured the scale-dependence and
luminosity-dependence of galaxy bias at z=1 (assuming CDM).Rise in bias on small
scales reflects physics of galaxy formation and
radial profile of galaxies in halos.
DEEP2 sample - large-scales: b =1.26 (0.04) - 1.54 (0.05)
Theoretical Modelling of (r)
Risa will talk about predicting the luminosity-dependent (r) using dark matter simulations and
assigning luminosities to halos:Conroy, Wechsler, Kravtsov astro-ph/0512234
Good agreement with our data implies that luminosity-dependence of clustering is driven by
mass of (sub)halos.
Zheng will talk about performing direct HOD fits to these results, measuring relation between galaxy
luminosity and halo mass and determining the halo mass distributions for central vs. satellite galaxies. We
are comparing with SDSS - measure evolution in HOD.
SDSS QSOs in DEEP2 fields
Coil et al., ApJ submitted
36 SDSS + 16 DEEP2 spectroscopic QSOs in the DEEP2 fields between z=0.7-1.4:
Work done w/ Joe Hennawi + Jeff
Newman
Clustering of Galaxies around QSOs
Clustering of DEEP2 galaxies around SDSS QSOs at z=0.7-1.4.
Errors include Poisson errors + cosmic variance.
Why measure the cross-correlation? Divide by the clustering of DEEP2 galaxies around DEEP2 galaxies to get the bias of QSO hosts…
Coil et al., ApJ submitted
Relative bias of QSOs to DEEP2 galaxies
The relative bias is ~1 +/-0.2
Galaxies that host QSOs at z=1 have the same clustering properties (same halo mass) as typical DEEP2 galaxies.
Don’t have same clustering as red/early-type galaxies (2 result) --- see the same result using local environment/overdensity
Places constraints on theoretical and semi-analytic models of quasars (Hopkins, Croton, etc.)
Coil et al., ApJ submitted
Summary
Have measured the luminosity-dependence of galaxy clustering at z=1 in the DEEP2 data. The clustering amplitude is lower than z=0.1 and can be explained as mass-dependent using a simple model to relate luminosity to dark matter halo mass.
See deviations from a power-law on small scales at z=1 for bright galaxies - due to sub-structure.
Directly measure the one-halo and two-halo components of (r) for galaxies in groups.
Can now model the HOD at z=1 and compare with z=0.1 to measure evolution.
Galaxies that host QSOs at z=1 reside in the same mass halos as typical DEEP2 galaxies.
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