Clusters, Galaxies and the COSMOS

Clusters, Galaxies and the COSMOS

J Berian James (IfA Edinburgh),John Peacock, Alexis Finoguenov,

Henry Joy McCracken & Gigi Guzzo

for the COSMOS collaboration

Berian James (IfA Edinburgh)

COSMOS – The Cosmic Evolution Survey

The primary goal of COSMOS is to study the relationship between large-scale structure and the formation of galaxies, dark matter, and nuclear activity in galaxies.

• 0.5 < z < 3

• 2 million objects (IAB ~ 27)

• Volume ~ SDSS/2dFGRS


COSMOS & Large-scale structure The assembly of galaxies, clusters and

dark matter on mass scales up to 1014; Reconstruction of the dark matter

distribution and content at z ~ 1.5; The redshift and environment evolution

of galaxy morphology, merger rates and star formation;

The evolution of AGN and dependence of black hole growth on galaxy morphology and environment; and

The clustering, mass and luminosity distribution of the earliest galaxies, AGN and intergalactic gas at 3 < z < 6.

VLA

Spitzer

HST (ACS)

Subaru

UKIRT

ESO-VLT

CHFT

NOAO

Galex

XMM

Chandra

Scoville et al., astro-ph/0612305


Data product: Catalogue of approximately 150 cluster locations, including photometric redshifts.

Clusters and galaxy groups VLA

Spitzer

HST (ACS)

Subaru

UKIRT

ESO-VLT

CHFT

NOAO

Galex

XMM

Chandra

e.g. Finoguenov et al., astro-ph/0612360


Optical galaxies Observations

Subaru broad-bands (B, V, r+, i+, z+) Intermediate- and narrow-bands

(redshift refinement and high-redshift galaxy search)

Data products Photometric, flux-calibrated images

(.05 mag rms) with absolute astrometry (0.1 x ACS pixel) over the full COSMOS field;

Million-source photometric redshift catalogue.

VLA

Spitzer

HST (ACS)

Subaru

UKIRT

ESO-VLT

CFHT

NOAO

Galex

XMM

Chandra

e.g. Capak et al., astro-ph/0704.2430


The galaxy-cluster cross-correlation


Projected cross-correlation function

Phleps et al.., A&A 468 113

Decompose the separation into line-of-sight (redshift) and transverse components;

The uncertainties in photometric redshifts cause distortion along line-of-sight;

To remove this effect, integrate along the line-of-sight.


The galaxy-cluster cross-correlation

Using 110 clusters at 0.3 < z < 1

Measurement is relative to cluster-random galaxy pairs; the latter reproduces the selection effects of the survey, but is otherwise Poisson-distributed.

Separation

Corr

ela

tion

am

plit

ud

e


Evolution with mass and redshift

3 redshift bins for 0 < z < 1.0

3 bins in log M from ~1012 to 1014

For each bin, measure wp with just the clusters in that bin;

To examine the trend in clustering, compare the amplitude at a fixed value of rp.

z increasing

M in

creasi

ng


Adaptive binning in the M-z plane

Division of the plane based on clusters available;

For each bin, measure wp with just the clusters in that bin;

Trends not obvious, but can be improved by optimising the number of clusters per bin

z

M


Summary The cluster-galaxy correlation displays evolution

with mass and with redshift; But at higher redshift, the survey probes higher

mass clusters, so how much of the redshift trend is really a trend in mass?

Can adaptive binning simultaneously capture the features of the trends in both mass and redshift?

The generation of random cluster catalogues would go some way to improving the result, by allowing the use of more sophisticated cross-correlation measures.

Clusters, Galaxies and the COSMOS

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