Evolution of Galaxies and their Environments at z = 0.1 to 3 in COSMOS
  Large-scale structures (LSS) out to z $< 3.0$ are measured in the Cosmic
Evolution Survey (COSMOS) using extremely accurate photometric redshifts
(photoz). The Ks-band selected sample (from Ultra-Vista) is comprised of
155,954 galaxies. Two techniques -- adaptive smoothing and Voronoi tessellation
-- are used to estimate the environmental densities within 127 redshift slices.
Approximately 250 statistically significant overdense structures are identified
out to z $= 3.0$ with shapes varying from elongated filamentary structures to
more circularly symmetric concentrations. We also compare the densities derived
for COSMOS with those based on semi-analytic predictions for a $\Lambda$CDM
simulation and find excellent overall agreement between the mean densities as a
function of redshift and the range of densities. The galaxy properties (stellar
mass, spectral energy distributions (SEDs) and star formation rates (SFRs)) are
strongly correlated with environmental density and redshift, particularly at z
$< 1.0 - 1.2$. Classifying the spectral type of each galaxy using the
rest-frame b-i color (from the photoz SED fitting), we find a strong
correlation of early type galaxies (E-Sa) with high density environments, while
the degree of environmental segregation varies systematically with redshift out
to z $\sim 1.3$. In the highest density regions, 80% of the galaxies are early
types at z=0.2 compared to only 20% at z = 1.5. The SFRs and the star formation
timescales exhibit clear environmental correlations. At z $> 0.8$, the star
formation rate density (SFRD) is uniformly distributed over all environmental
density percentiles, while at lower redshifts the dominant contribution is
shifted to galaxies in lower density environments.
