The Deep2 Galaxy Redshift Survey: Evolution of the Color-density Relation At

Using a sample of 19,464 galaxies drawn from the DEEP2 Galaxy Redshift Survey, we study the relationship between galaxy color and environment at 0.4 < z < 1.35. We find that the fraction of galaxies on the red sequence depends strongly on local environment out to z > 1, being larger in regions of greater galaxy density. At all epochs probed, we also find a small population of red, morphologically early-type galaxies residing in regions of low measured overdensity. The observed correlations between the red fraction and local overdensity are highly significant, with the trend at z > 1 detected at a greater than 5σ level. Over the entire redshift regime studied, we find that the color-density relation evolves continuously, with red galaxies more strongly favoring overdense regions at low z relative to their red-sequence counterparts at high redshift. At z ∼ 1.3, the red fraction only weakly correlates with overdensity, implying that any color dependence to the clustering of ∼ L galaxies at that epoch must be small. Our findings add weight to existing evidence that the build-up of galaxies on the red sequence has occurred preferentially in overdense environments (i.e., galaxy groups) at z . 1.5. The strength of the observed evolutionary trends at 0 < z < 1.35 suggests that the correlations observed locally, such as the morphology-density and color-density relations, are the result of environment-driven mechanisms (i.e., “nurture”) and do not appear to have been imprinted (by “nature”) upon the galaxy population during their epoch of formation. Subject headings: galaxies:high-redshift, galaxies:evolution, galaxies:statistics, galaxies: funamental parameters, large-scale structure of universe