{
  "id": "1603.04855",
  "version": "v1",
  "published": "2016-03-15T20:00:03.000Z",
  "updated": "2016-03-15T20:00:03.000Z",
  "title": "Organized Chaos: Scatter in the relation between stellar mass and halo mass in small galaxies",
  "authors": [
    "Shea Garrison-Kimmel",
    "James S. Bullock",
    "Michael Boylan-Kolchin",
    "Emma Bardwell"
  ],
  "comment": "13 pages, 6 figures, 1 table. Submitted to MNRAS; comments welcome",
  "categories": [
    "astro-ph.GA",
    "astro-ph.CO"
  ],
  "abstract": "We use Local Group galaxy counts together with the ELVIS N-body simulations to jointly constrain the scatter and slope in the stellar mass vs. halo mass relation at low masses, $M_\\star \\simeq 10^5 - 10^8 M_\\odot$. Assuming log-normal scatter about a median relation of the form $M_\\star \\propto M_{\\rm halo}^\\alpha$, the preferred log-slope steepens from $\\alpha \\simeq 1.8$ in the limit of zero scatter to $\\alpha \\simeq 2.6$ in the case of 2 dex of scatter in $M_\\star$ at fixed halo mass. We provide fitting functions for the best-fit relations as a function of scatter, including cases where the relation becomes increasingly stochastic with decreasing mass. We show that if the scatter at fixed halo mass is large enough ($\\gtrsim 1$ dex) and if the median relation is steep enough ($\\alpha \\gtrsim 2$), then the \"too-big-to-fail\" problem seen in the Local Group can be self-consistently eliminated in about $\\sim 5-10\\%$ of realizations. This scenario requires that the most massive subhalos host unobservable ultra-faint dwarfs fairly often; we discuss potentially observable signatures of these systems. Finally, we compare our derived constraints to recent high-resolution simulations of dwarf galaxy formation in the literature. Though simulation-to-simulation scatter in $M_\\star$ at fixed $M_{\\rm halo}$ is large among separate authors ($\\sim 2$ dex), individual codes produce relations with much less scatter and usually give relations that would over-produce local galaxy counts.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2016-03-15T20:00:03.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "stellar mass",
      "small galaxies",
      "organized chaos",
      "fixed halo mass",
      "over-produce local galaxy counts"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 13,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "adsabs": "2016arXiv160304855G",
      "inspire": 1428624
    }
  }
}