{
  "id": "1411.2590",
  "version": "v1",
  "published": "2014-11-10T21:00:02.000Z",
  "updated": "2014-11-10T21:00:02.000Z",
  "title": "The suppression of direct collapse black hole formation by soft X-ray irradiation",
  "authors": [
    "Kohei Inayoshi",
    "Takamitsu L. Tanaka"
  ],
  "comment": "12 pages, 5 figures, 2 tables, submitted to MNRAS",
  "categories": [
    "astro-ph.GA",
    "astro-ph.CO"
  ],
  "abstract": "The origins of supermassive black holes (SMBHs) in galactic nuclei is one of the major unsolved problems in astrophysics. One hypothesis is that they grew from >10^5 Msun black holes that formed in the `direct collapse' of massive gas clouds that have low concentrations of both metals and molecular hydrogen (H2). Such clouds could form in the early (z>10) Universe if pre-galactic gas is irradiated by H2-photodissociating, far-ultraviolet (FUV) light from a nearby star-forming galaxy. The key uncertainties with this scenario are (1) how strong the FUV flux must be to sufficiently suppress the H2 abundance to prevent fragmentation and ordinary star formation; and (2) whether the requisite conditions arise frequently enough in nature to account for the observed number density of SMBHs (luminous quasars) at high redshifts. In this work, we re-examine the critical FUV flux J_crit that is required to keep H2 photodissociated and lead to direct collapse. We show that J_crit could be much higher than previously believed if the same FUV sources also produce X-rays, which can work to offset H2 photodissociation by increasing the ionization fraction and promoting H2 formation via electron-catalyzed reactions. We stress that soft (~ 1 keV) X-rays are far more effective at promoting H2 formation than hard (~ 10 keV) X-rays. Further, we estimate how much soft X-rays can suppress the number density of direct-collapse black holes compared to previous calculations. We find that, even for conservative sets of assumptions, if J_crit is higher than 400-1000 then direct collapse would occur too rarely to explain the observed abundance of z>6 quasars.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2014-11-10T21:00:02.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "direct collapse black hole formation",
      "soft x-ray irradiation",
      "promoting h2 formation"
    ],
    "publication": {
      "doi": "10.1093/mnras/stv871",
      "journal": "Monthly Notices of the Royal Astronomical Society",
      "year": 2015,
      "month": "Jul",
      "volume": 450,
      "number": 4,
      "pages": 4350
    },
    "note": {
      "typesetting": "TeX",
      "pages": 12,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 1327183,
      "adsabs": "2015MNRAS.450.4350I"
    }
  }
}