Hydrodynamical simulations of galaxy properties: Environmental effects

Using N-body + hydro simulations we study relations between the local envir onments of galaxies on approximate to 0.5 Mpc scale and properties of the l uminous components of galaxies. Our numerical simulations include effects o f star formation and supernova feedback in different cosmological scenarios : the standard COBE-normalized Cold Dark Matter model (CDM), its variant, t he Broken Scale Invariance model (BSI), and a model with cosmological const ant (Lambda CDM). The present time corresponds to quite different stages of clustering in these three models, and the range of environments reflects t hese differences. In this paper, we concentrate on the effects of environme nt on colors and morphologies of galaxies, on the star formation rate and o n the relation between the total luminosity of a galaxy and its circular ve locity. We demonstrate a statistically significant theoretical relationship between morphology and environment. In particular, there is a strong tende ncy for high-mass galaxies and for elliptical galaxies to form in denser en vironments, in agreement with observations. We find that in models with den ser environments (CDM scenario) similar to 13% of the galactic halos can be identified as field ellipticals, according to their colors. In simulations with less clustering (BSI and Lambda CDM), the fraction of ellipticals is considerably lower ( similar to 2 - 3%). The strong sensitivity of morpholo gical type to environment is rather remarkable because our results are appl icable 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 ga laxies in our simulations are included, we find a statistically significant dependence of the galaxy luminosity-circular velocity relation on dark mat ter overdensity within spheres of radius of 0.5 Mpc, for the CDM simulation s. But if we remove "elliptical'' galaxies from our analysis to mimic the T ully-Fisher relation for spirals, then no dependence is found in any model. (C) 1999 Elsevier Science B.V. All rights reserved.