Gravitational potential environment of galaxies. I. Simulation

Abstract

We extend the concept of galaxy environment from the local galaxy number density to the gravitational potential and its functions like the shear tensor. For this purpose, we examine whether or not one can make an accurate estimation of the gravitational potential from an observational sample which is finite in volume, biased due to galaxy biasing, and subject to redshift space distortion. Dark halos in a ΛCDM simulation are used in this test. We find that one needs to stay away from the sample boundaries by more than 30h -1Mpc to reduce the error within 20% of the rms values of the potential or the shear tensor. The error due to the galaxy biasing can be significantly reduced by using the galaxy mass density field instead of the galaxy number density field. The error caused by the redshift space distortion can be effectively removed by correcting galaxy positions for the peculiar velocity effects. We inspect the dependence of dark matter halo properties on four environmental parameters: local density, gravitational potential, and the ellipticity, and prolateness of the shear tensor. We find that the local density has the strongest correlation with halo properties. This is evident that the internal physical properties of dark halos are mainly controlled by small-scale physics. In high-density regions dark halos are on average more massive and spherical and have higher spin parameter and velocity dispersion. We also study the relation between the environmental parameters and the subtypes of dark halos. The spin parameter of satellite halos depends only weakly on the local density for all mass ranges studied, while that of isolated or central halos depends more sensitively on the local density. The gravitational potential and the shear tensor have weaker correlations with halo properties, but have environmental information independent of the local density. © 2010. The American Astronomical Society. All rights reserved.