{
  "id": "1702.06129",
  "version": "v1",
  "published": "2017-02-20T19:00:03.000Z",
  "updated": "2017-02-20T19:00:03.000Z",
  "title": "Local Group Ultra-Faint Dwarf Galaxies in the Reionization Era",
  "authors": [
    "Daniel R. Weisz",
    "Michael Boylan-Kolchin"
  ],
  "comment": "6 pages, 4 Figures. Submitted to MNRAS. Comments welcome",
  "categories": [
    "astro-ph.GA",
    "astro-ph.CO"
  ],
  "abstract": "Motivated by the stellar fossil record of Local Group (LG) dwarf galaxies, we show that the star-forming ancestors of the faintest ultra-faint dwarf galaxies (UFDs; ${\\rm M}_{\\rm V}$ $\\sim -2$ or ${\\rm M}_{\\star}$ $\\sim 10^{2}$ at $z=0$) had ultra-violet (UV) luminosities of ${\\rm M}_{\\rm UV}$ $\\sim -3$ to $-6$ during reionization ($z\\sim6-10$). The existence of such faint galaxies has substantial implications for early epochs of galaxy formation and reionization. If the faint-end slopes of the UV luminosity functions (UVLFs) during reionization are steep ($\\alpha\\lesssim-2$) to ${\\rm M}_{\\rm UV}$ $\\sim -3$, then: (i) the ancestors of UFDs produced $>50$% of UV flux from galaxies; (ii) galaxies can maintain reionization with escape fractions that are $>$2 times lower than currently-adopted values; (iii) direct HST and JWST observations may detect only $\\sim10-50$% of the UV light from galaxies; (iv) the cosmic star formation history increases by $\\gtrsim4-6$ at $z\\gtrsim6$. Significant flux from UFDs, and resultant tensions with LG dwarf galaxy counts, are reduced if the high-redshift UVLF turns over. Independent of the UVLF shape, the existence of a large population of UFDs requires a non-zero luminosity function to ${\\rm M}_{\\rm UV}$ $\\sim -3$ during reionization.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2017-02-20T19:00:03.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "dwarf galaxy",
      "local group ultra-faint dwarf galaxies",
      "reionization era",
      "cosmic star formation history increases",
      "luminosity function"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 6,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}