Large Scale Structure in Dark Matter and Galaxies

Galaxy evolution and AGN growth in the early universe are believed to be strongly driven by merging (hierarchical growth) and galaxy dynamical interactions. Thus, a full exploration of the environmental influences is absolutely essential to understanding this early evolution. The Cosmic Evolution Survey (COSMOS, Scoville et al. (2007a)) is specifically designed to probe the correlated coevolution of galaxies, star formation, active galactic nuclei (AGN) and dark matter (DM) large-scale structures (LSS) over the redshift range z > 0.5 to 3. The survey includes multi-wavelength imaging and spectroscopy from X-ray to radio wavelengths covering a 2 square degree equatorial field. Photometric redshifts are derived for 800,000 galaxies with accuracy reaching sigma(z)/(1 + z) = 0.7 - 1.6% for bright galaxies (I-AB = 22 - 24mag). Deep imaging with Subaru S-CAM has been instrumental to these accurate photo-z at faint magnitudes (Taniguchi et al. 2007). Large scale structures have been traced in COSMOS from z = 0.2 to 2.5 in the baryons (from galaxy density distribution) and in the dark matter to z = 1.1 (from weak lensing). These LSS extend over 20 Mpc with total mass tip to similar to 10(15)M(circle dot). The overall distribution of galaxy overdensities agrees well with those predicted from the Millennium simulation. A trend for an increasingly high overdensity toward low z is clearly apparent in these data. The median galaxy spectral energy distribution (SED) and star formation rate (SFR) is seen to vary systematically with both redshift and environmental density - early type SEDs and lower SFRs in denser regions and at lower redshift. This evolution is probably driven by the exhaustion of the ISM and by galaxy interactions. Strong evolution is seen the frequency of close pairs of galaxies - particularly for lower mass companions at projected separations 10 - 20 kpc.