Galaxy star formation in different environments

Abstract

We use a semi-analytic model of galaxy formation to study signatures of large-scale modulations in the star formation (SF) activity in galaxies. In order to do this we carefully define local and global estimators of the density around galaxies. The former are computed using a voronoi tessellation technique and the latter are parameterised by the normalised distance to haloes and voids, in terms of the virial and void radii, respectively. As a function of local density, galaxies show a strong modulation in their SF, a result that is in agreement with those from several authors. When taking subsamples of equal local density at different large-scale environments, we find relevant global effects whereby the fraction of red galaxies diminishes for galaxies in equal local density environments farther away from clusters and closer to voids. In general, the semianalytic simulation is in good agreement with the available observational results, and offers the possibility to disentangle many of the processes responsible for the variation of galaxy properties with the environment; we find that the changes found in samples of galaxies with equal local environment but different distances to haloes or voids come from the variations in the underlying mass function of dark-matter haloes. There is an additional possible effect coming from the host dark-matter halo ages, indicating that halo assembly also plays a small but significant role ($1.14\sigma$) in shaping the properties of galaxies, and in particular, hints at a possible spatial correlation in halo/stellar mass ages.