Environmental dependence of dark matter halo growth - I. Halo merger rates
Abstract
In an earlier paper, we quantified the mean merger rate of dark matter haloes as a function of redshift z, descendant halo mass M0, and progenitor halo mass ratio ξ using the Millennium simulation of the Λ cold dark matter cosmology. Here, we broaden that study and investigate the dependence of the merger rate of haloes on their surrounding environment. A number of local mass overdensity variables, both including and excluding the halo mass itself, are tested as measures of a halo's environment. The simple functional dependence on z, M0, and ξ of the merger rate found in our earlier work, is largely preserved in different environments, but we find that the overall amplitude of the merger rate has a strong positive correlation with the environmental densities. For galaxy-mass haloes, we find mergers to occur ~2.5 times more frequently in the densest regions than in voids at both z = 0 and higher redshifts. Higher mass haloes show similar trends. We present a fitting form for this environmental dependence that is a function of both mass and local density and valid out to z = 2. The amplitude of the progenitor (or conditional) mass function shows a similar correlation with local overdensity, suggesting that the extended Press-Schechter model for halo growth needs to be modified to incorporate environmental effects.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- April 2009
- DOI:
- 10.1111/j.1365-2966.2009.14480.x
- arXiv:
- arXiv:0808.2471
- Bibcode:
- 2009MNRAS.394.1825F
- Keywords:
-
- galaxy: formation;
- galaxy: halo;
- cosmology: theory;
- dark matter;
- large-scale structure of Universe;
- Astrophysics
- E-Print:
- 14 pages, 8 figures, Moderate revisions in version 2. Accepted in MNRAS