ESA Science & Technology - Large structures and galaxy evolution in COSMOS at z < 1.1

Publication date: 14 December 2006

Authors: Scoville, N. et al.

Year: 2006

E-print arXiv:astro-ph/0612384, for ApJS COSMOS Special Issue, 2007 in press

We present the first identification of large-scale structures (LSS) at z < 1.1 in the Cosmic Evolution Survey (COSMOS). The structures are identified from adaptive smoothing of galaxy counts in the pseudo-3d space (R.A., Dec., z) using the COSMOS photometric redshift catalog. The technique is tested on a simulation including galaxies distributed in model clusters and a field galaxy population - recovering structures on all scales from 1 to 202 without a priori assumptions for the structure size or density profile. Our procedure makes no a priori selection on galaxy spectral energy distribution (SED, for example the Red Sequence), enabling an unbiased investigation of environmental effects on galaxy evolution. The COSMOS photometric redshift catalog yields a sample of 1.5 × 10⁵ galaxies with redshift accuracy, delta z_FWHM/(1 + z) d 0.1 at z < 1.1 down to I_AB d 25 mag. Using this sample of galaxies, we identify 42 large-scale structures and clusters. Projected surface-density maps for the structures indicate multiple peaks and internal structure in many of the most massive LSS. The stellar masses (determined from the galactic SEDs) for the LSS range from M_* ~ 10¹¹ up to ~ 3 × 10¹³ Msun. Five LSS have total stellar masses exceeding 10¹³ Msun. (Total masses including non-stellar baryons and dark matter are expected to be ~ 50 - 100 times greater.) The derived mass function for the LSS is consistent (within the expected Poisson and cosmic variances) with those derived from optical and X-ray studies at lower redshift.