Alison Coil UC-Berkeley

for the DEEP2 Survey Team

August 2004

Galaxy Clustering and Environment Results from the DEEP2 Survey

The DEEP2 Collaboration

U.C. Berkeley: M. Davis (PI), A. Coil, M. Cooper, B. Gerke, R. Yan, C. Conroy

U.C. Santa Cruz: S. Faber (Co-PI), D. Koo, P. Guhathakurta, D. Phillips, C. Willmer, B. Weiner, R. Schiavon, K. Noeske, A. Metevier, L. Lin, N. Konidaris, G. Graves

Hawaii: N. Kaiser LBNL: J. Newman U. Pitt.: A. Connolly JPL: P. Eisenhardt Princeton: D. Finkbeiner

A Redshift Survey at z=1:

The DEEP2 Galaxy Redshift Survey, which uses the DEIMOS spectrograph on the Keck II telescope, will study both galaxy

properties and the clustering of galaxies at z=1.

• 3.5 sq. degrees • 4 fields (0.5o x 2o)• primary z~0.7-1.4• ~50,000 redshifts• ~6·106 h-3 Mpc3

• 90 Keck nights• One-hour exposures• RAB=24.1

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 Mpc3)

Number of Galaxiesz~0z~1

DEEP2

SDSS

2dF

CFA+SSRS

Comparison with local samples:

LCRS

PSCZ

Our color cuts are highly successful!

By applying a relatively simple BRI color cut, we have a sample that is 13% z<0.75, vs. >60% with no cut.Only 3% of objects that we reject are at z>0.75.

In the Extended Groth Strip, we apply no color cut, enhancing multiwavelength studies and also making this test possible.

DEEP2 vs. previous surveys of distant galaxies

Galaxies found in large numbers well beyond z=1

Obs. R-I

Rest U-B

Color bimodality

note the z=0.7 color cut

Slitmask spectroscopy

Using custom-milled slitmasks with DEIMOS we are obtaining spectra of ~120 targets at a time. A total of 480 slitmasks will be required for the survey; we can tilt slits up to 30 degrees to obtain rotation curves.

A fully automated reduction pipeline

A few percent of one DEEP2 mask, rectified, flat-fielded, CR cleaned, wavelength-rectified, and sky subtracted. Note the resolved [OII] doublets. Shown is a small group of galaxies with velocity dispersion 250 km/s at

z1. Note the clean residuals of sky lines!

SDSS spectral pipeline code by Schlegel et al. allowed us to rapidly develop a full 2d and 1d spectral reduction pipeline that is completely automated. Check z’s by eye.

Status of the DEEP2 Survey

• DEIMOS commissioning began June 2002 under clear skies and was extremely successful.

• DEEP2 observing campaign began in July 2002. At the end of 3 semesters of the 6 planned, we had completed 48% of the survey slitmasks! We are on schedule!

• Observations complete mid-2005.

Currently ~60% done!

Clustering in DEEP2: First Redshift Maps

Projected maps of two DEEP2 pointings (of 13 total). Red = early-type (from PCA).

2-point correlation function: (r)

From the projected function wp(rp) we can recover the real-space correlation

function (r)= (r0/r)

z=0.7-0.9: r0=3.53 +/-0.81z=0.9-1.35: r0=3.12 +/-0.72

both have slope = 1.66 +/-0.12Errors are estimated using mock catalogs - dominated by cosmic variance

(r) follows a power-law prescription locally:

(r) = (r0/r) with r0~5 Mpc/h and ~1.8.

r0 = scale where the probability of finding a galaxy pair is 2x random

Galaxy bias: galaxy/dark matter clustering

Bias evolves with redshift: z=3: b~4 z=0: b~1

Galaxy formation simulation by Kauffmann et al. grey=dark matter particles colors=galaxies

DEEP2 sample as a whole: b=0.96 +/-0.13 for 8=1 today

b=1.19 +/-0.16 for 8=0.8 todaycould be the result of our R-band target selection – we’re under-

sampling older, red stellar populations

Coil et al. 2004 astro-ph/0305586

Clustering as a function of Color and Spectral Type

Redder galaxies have a larger correlation length and larger velocity dispersion, as do absorption-line galaxies:

reside in more clustered / dense environments.

Red galaxies:dashed lines

Blue galaxies: solid lines

Galaxy Clustering: color, type, luminosity

Redder, passively-evolving and/or more luminous galaxies cluster more strongly than bluer, star-forming, less luminous galaxies - similar as z~0

results

ColorB-R>0.7: r0= 4.32 (0.73) =1.84 (0.07)B-R<0.7: r0= 2.81 (0.48) =1.52 (0.06)

Spectral TypeAbsorption: r0= 6.61 (1.12) =1.48 (0.06)Emission: r0= 3.17 (0.54) =1.68 (0.07)

LuminosityBrighter MB<-19.75: r0= 3.70 (0.65) =1.60 (0.06)Fainter MB>-19.75: r0= 2.80 (0.48) =1.54 (0.06)

Projected Angular 2-pt corr. fnct: Have photometry for many more galaxies than spectra:

~350,000 galaxies over 5 deg2, incl. z<0.7Projected angular 2-point correlation function:

Constrain the 3d galaxy clustering (r) * if the z dist. of the sources is known

7” 3’

slope = -0.8:

Smooth decrease in clustering with magnitude. Errors are variance across 15 pointings.

Evolution of Galaxy Clustering

(r,z)=(r,z=0) (1+z) –(3+)

=-1.2 fixed in comoving coords.=0 fixed in proper coords.

>0 clustering grows in proper coords.

We find no single value of fits our data – must evolve with z.We see significant growth in the clustering amplitude from z>1 to 0.

Use DEEP2 spectroscopic sample to measure the redshift distribution of sources in various

magnitude ranges. Data is from the Groth Strip where we have no photo-z cut – 3320

galaxies.

dn/dz=A z2 e(-z/z0)/z03

Angular correlation function is an integral of the 3-d clustering along the line of sight.

Angular Clustering as fnct. of R-I color

redblueIn addition to a trend of redder

galaxies being more clustered, the bluest galaxies (R-I <0.2) are also

highly clustered – unexpected!

blue

red

Redshift distribution of color samples:

Reddest galaxies are at z~0.85, narrow Bluer samples are at lower z, wider

Bluest samples have significant components at z<0.5 and z~1.7

Clustering as a function of R-I color

Reddest galaxies are likely z>0.5 progenitors of local ellipticals

Bluest galaxies are a mix of brightest objects at z>1.4, local faint blue dwarfs,

and AGN between z~0-2

Corrected for z>1.4 galaxies

Coil et al. 2004 astro-ph/0403423

Galaxy properties and environment Measure galaxy environment using projected Nth-nearest neighbor

distance. See strong trends of restframe color and OII equivalent width with environment. No residual trend in OII EW once the

correlation of environment with color is removed.

Cooper et al. in prepblue color red

envi

ronm

ent

OII equivalent width

Color-magnitude vs environment

Redder galaxies reside in denser environments, with the brightest red galaxies in the most dense environments. Within the blue galaxy population, the brightest also lie in the most dense environments - progenitors of central

cluster galaxies at z~0?

Bright blue galaxies in densest environments

Color vs mag. w/ density contoursdarker regions = more dense

Galaxy Groups and Clusters in DEEP2

Gerke et al. in prep

red=pairs; blue=N>2; sizelog () log (halo mass)

Voronoi-based methods can also be used to identify clusters and groups of galaxies (Marinoni et al. 2002).

DEEP2 group catalogs in two of our pointings will be published shortly.

This will allow both the study of group property distributions and of group vs. field galaxies.

red=absorption-dominated

Now looking at group correlations and void statistics…

Coil et al. in prep

Group-group correlation function is larger than the galaxy-galaxy correlation function. Field galaxies are less clustered than the full galaxy sample, which is less clustered than galaxies in groups.

Conclusions

1. r0~3.5 Mpc/h at z~1, b~1.0-1.2 for DEEP2 galaxies.2. Red, passively-evolving galaxies have larger fingers of God and r0

than blue, star-forming galaxies at z~1.3. See some luminosity-dependence in the clustering strength.4. Strong dependence of angular clustering on observed color:

red galaxies at z~0.8 have r0~6.5 Mpc/h blue galaxies at z>1.4 have r0>~5 Mpc/h

Galaxy Clustering:

Environment:1. Color and OII EW correlate strongly with local environment at z~1.

2. Find a population of bright blue galaxies in the densest environments at z~1 which do not exist at z~0 - central cluster galaxies?