Environmental dependence of dark matter halo growth – I. Halo merger rates |
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Authors: | Onsi Fakhouri Chung-Pei Ma |
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Institution: | Department of Astronomy, 601 Campbell Hall, University of California, Berkeley, CA 94720, USA |
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Abstract: | In an earlier paper, we quantified the mean merger rate of dark matter haloes as a function of redshift z , descendant halo mass M 0, 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 , M 0 , 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. |
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Keywords: | galaxy: formation galaxy: halo cosmology: theory dark matter large-scale structure of Universe |
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