{
  "id": "1502.01339",
  "version": "v1",
  "published": "2015-02-04T21:00:01.000Z",
  "updated": "2015-02-04T21:00:01.000Z",
  "title": "The merger rate of galaxies in the Illustris Simulation: a comparison with observations and semi-empirical models",
  "authors": [
    "Vicente Rodriguez-Gomez",
    "Shy Genel",
    "Mark Vogelsberger",
    "Debora Sijacki",
    "Annalisa Pillepich",
    "Laura V. Sales",
    "Paul Torrey",
    "Greg Snyder",
    "Dylan Nelson",
    "Volker Springel",
    "Chung-Pei Ma",
    "Lars Hernquist"
  ],
  "comment": "17 pages, 10 figures, submitted to MNRAS. Comments welcome",
  "categories": [
    "astro-ph.GA",
    "astro-ph.CO"
  ],
  "abstract": "We have constructed merger trees for galaxies in the Illustris Simulation by directly tracking the baryonic content of subhalos. These merger trees are used to calculate the galaxy-galaxy merger rate as a function of descendant stellar mass, progenitor stellar mass ratio, and redshift. We demonstrate that the most appropriate definition for the mass ratio of a galaxy-galaxy merger consists in taking both progenitor masses at the time when the secondary progenitor reaches its maximum stellar mass. Additionally, we avoid effects from `orphaned' galaxies by allowing some objects to `skip' a snapshot when finding a descendant, and by only considering mergers which show a well-defined `infall' moment. Adopting these definitions, we obtain well-converged predictions for the galaxy-galaxy merger rate with the following main features, which are qualitatively similar to the halo-halo merger rate except for the last one: a strong correlation with redshift that evolves as $\\sim (1+z)^{2.4-2.8}$, a power law with respect to mass ratio, and an increasing dependence on descendant stellar mass, which steepens significantly for descendant stellar masses greater than $\\sim 2 \\times 10^{11} \\, {\\rm M_{\\odot}}$. These trends are consistent with observational constraints for medium-sized galaxies ($M_{\\ast} \\gtrsim 10^{10} \\, {\\rm M_{\\odot}}$), but in tension with some recent observations of the close pair fraction for massive galaxies ($M_{\\ast} \\gtrsim 10^{11} \\, {\\rm M_{\\odot}}$), which report a nearly constant or decreasing evolution with redshift. Finally, we provide a fitting function for the galaxy-galaxy merger rate which is accurate over a wide range of stellar masses, progenitor mass ratios, and redshifts.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2015-02-04T21:00:01.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "illustris simulation",
      "galaxy-galaxy merger rate",
      "semi-empirical models",
      "observations",
      "descendant stellar masses greater"
    ],
    "publication": {
      "doi": "10.1093/mnras/stv264"
    },
    "note": {
      "typesetting": "TeX",
      "pages": 17,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 1343056
    }
  }
}