Hydrodynamical simulations of galaxy properties: Environmental effects

Using N-body + hydro simulations we study relations between the local environments of galaxies on ≈0.5 Mpc scale and properties of the luminous components of galaxies. Our numerical simulations include effects of star formation and supernova feedback in different cosmological scenarios: the standard COBE-normalized Cold Dark Matter model (CDM), its variant, the Broken Scale Invariance model (BSI), and a model with cosmological constant (ΛCDM). The present time corresponds to quite different stages of clustering in these three models, and the range of environments reflects these differences. In this paper, we concentrate on the effects of environment on colors and morphologies of galaxies, on the star formation rate and on the relation between the total luminosity of a galaxy and its circular velocity. We demonstrate a statistically significant theoretical relationship between morphology and environment. In particular, there is a strong tendency for high-mass galaxies and for elliptical galaxies to form in denser environments, in agreement with observations. We find that in models with denser environments (CDM scenario) ∼13% of the galactic halos can be identified as field ellipticals, according to their colors. In simulations with less clustering (BSI and ΛCDM), the fraction of ellipticals is considerably lower (∼2-3%). The strong sensitivity of morphological type to environment is rather remarkable because our results are applicable to "field" galaxies and small groups. Because of small box size (5 Mpc) we did not have large groups or clusters in our simulations. If all galaxies in our simulations are included, we find a statistically significant dependence of the galaxy luminosity-circular velocity relation on dark matter overdensity within spheres of radius of 0.5 Mpc, for the CDM simulations. But if we remove "elliptical" galaxies from our analysis to mimic the Tully-Fisher relation for spirals, then no dependence is found in any model.