2010/01/31 by Onsi Fakhouri, Chung-Pei Ma, Michael Boylan-Kolchin · 2 citations
Physics and Astronomy · #astro-ph.CO
paper · pdf · doi:10.1111/j.1365-2966.2010.16859.x
published as Mon.Not.Roy.Astron.Soc.406:2267,2010 · 12 pages, 9 figures, accepted in MNRAS
arxiv created 2010/04/30 · arxiv updated 2010/10/26
We construct merger trees of dark matter haloes and quantify their merger rates and mass growth rates using the joint dataset from the Millennium and Millennium-II simulations. The finer resolution of the Millennium-II Simulation has allowed us to extend our earlier analysis of halo merger statistics to an unprecedentedly wide range of descendant halo mass (1010 < M0 < 1015 Msun), progenitor mass ratio (10-5 < xi < 1), and redshift (0 < z < 15). We update our earlier fitting form for the mean merger rate per halo as a function of M0, xi, and z. The overall behavior of this quantity is unchanged: the rate per unit redshift is nearly independent of z out to z~15; the dependence on halo mass is weak (M00.13); and it is nearly a power law in the progenitor mass ratio (xi-2). We also present a simple and accurate fitting formula for the mean mass growth rate of haloes as a function of mass and redshift. This mean rate is 46 Msun/yr for 1012 Msun haloes at z=0, and it increases with mass as M1.1 and with redshift as (1+z)2.5 (for z > 1). When the fit for the mean mass growth rate is integrated over a halo's history, we find excellent match to the mean mass assembly histories of the simulated haloes. By combining merger rates and mass assembly histories, we present results for the number of mergers over a halo's history and the statistics of the redshift of the last major merger.