{
  "id": "1502.06958",
  "version": "v1",
  "published": "2015-02-24T21:00:03.000Z",
  "updated": "2015-02-24T21:00:03.000Z",
  "title": "An X-ray Selected Sample of Candidate Black Holes in Dwarf Galaxies",
  "authors": [
    "Sean Lemons",
    "Amy Reines",
    "Richard Plotkin",
    "Elena Gallo",
    "Jenny Greene"
  ],
  "comment": "Accepted for publication in the Astrophysical Journal",
  "categories": [
    "astro-ph.GA",
    "astro-ph.HE"
  ],
  "abstract": "We present a sample of hard X-ray selected candidate black holes (BHs) in 19 dwarf galaxies. BH candidates are identified by cross-matching a parent sample of ~44,000 local dwarf galaxies (M_stellar < 3 x 10^9 Msun, z<0.055) with the Chandra Source Catalog, and subsequently analyzing the original X-ray data products for matched sources. Of the 19 dwarf galaxies in our sample, 8 have X-ray detections reported here for the first time. We find a total of 43 point-like hard X-ray sources with individual luminosities L(2-10 keV) ~ 10^37 - 10^40 erg/s. Hard X-ray luminosities in this range can be attained by stellar-mass X-ray binaries (XRBs), and by massive BHs accreting at low Eddington ratio. We place an upper limit of 53% (10/19) on the fraction of galaxies in our sample hosting a detectable hard X-ray source consistent with the optical nucleus, although the galaxy center is poorly defined in many of our objects. We also find that 42% (8/19) of the galaxies in our sample exhibit statistically significant enhanced hard X-ray emission relative to the expected galaxy-wide contribution from low-mass and high-mass XRBs, based on the L(2-10 keV)-M_stellar-SFR relation defined by more massive and luminous systems. For the majority of these X-ray enhanced dwarf galaxies, the excess emission is consistent with (but not necessarily due to) a nuclear X-ray source. Follow-up observations are necessary to distinguish between stellar-mass XRBs and active galactic nuclei powered by more massive BHs. In any case, our results support the notion that X-ray emitting BHs in low-mass dwarf galaxies may have had an appreciable impact on reionization in the early Universe.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2015-02-24T21:00:03.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "dwarf galaxies",
      "x-ray selected sample",
      "hard x-ray source consistent",
      "selected candidate black holes",
      "x-ray selected candidate black"
    ],
    "publication": {
      "doi": "10.1088/0004-637X/805/1/12"
    },
    "note": {
      "typesetting": "TeX",
      "pages": 0,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 1346358
    }
  }
}