{
  "id": "1402.2279",
  "version": "v3",
  "published": "2014-02-10T21:00:10.000Z",
  "updated": "2015-05-05T13:33:03.000Z",
  "title": "The origin of the Far-infrared continuum of z ~ 6 quasars: a radiative transfer model for SDSS J1148+5251",
  "authors": [
    "Raffaella Schneider",
    "Simone Bianchi",
    "Rosa Valiante",
    "Guido Risaliti",
    "Stefania Salvadori"
  ],
  "comment": "11 pages, 5 figures, to appear in A&A",
  "categories": [
    "astro-ph.GA",
    "astro-ph.CO"
  ],
  "abstract": "We investigate the origin of the FIR continuum of SDSS J1148+5251, using it as a prototype for the more general class of high-luminosity high-redshift QSOs. We run the radiative transfer code TRADING to follow the transfer of radiation from the central source and from stellar sources through the dusty environment of the host galaxy. The model is based on the output of the semi-analytical merger tree code, GAMETE/QSOdust, which enables to predict the evolution of the host galaxy and of its nuclear black hole, following the star formation history and chemical evolution -- including dust -- in all the progenitor galaxies of SDSS J1148+5251. We find that the radiation emitted by the central source can also provide an important source of heating for the dust distributed in the host galaxy, powering at least 30% and up to 70% of the observed far infrared emission at rest-frame wavelengths [20 - 1000]micron. The remaining fraction is contributed by stellar sources and can only be achieved if the host galaxy is able to sustain a star formation rate of ~ 900 Msun/yr at z=6.4. This points to a co-evolution scenario where, during their hierarchical assembly, the first SMBHs and their host galaxies first grow at the same pace until the black hole reaches a mass of ~ 2 10^8 Msun and starts growing faster than its host, reaching the bright quasar phase when the black hole and stellar mass fall within the scatter of the scaling relation observed in local galaxies. This same evolutionary scenario has been recently shown to explain the properties of a larger sample of 5 < z <6.4 QSOs, and imply that current dynamical mass measurements may have missed an important fraction of the host galaxy stellar mass. We conclude that the FIR luminosity of high-z quasars is a sensitive tracer of the rapidly changing physical conditions in the host galaxy.",
  "revisions": [
    {
      "version": "v2",
      "updated": "2014-02-12T14:42:19.000Z",
      "title": "The spectral energy distribution of z ~ 6 quasars: the case of SDSS J1148+5251",
      "abstract": "We investigate the origin of the spectral energy distribution of SDSS J1148+5251, using it as a prototype for the more general class of high-luminosity high-redshift quasars. To this aim, we run the radiative transfer code TRADING using a simple model for the central source,including all the radiation that can travel beyond the dusty torus, and following the transfer of radiation from the central source and from stellar sources through the dusty environment of the host galaxy. Comparing the model predictions with the observational data, including the recently published Herschel detections, we find that the spectral energy distribution of SDSSJ1148+5251 points to an evolutionary scenario where ~ 60% of the observed FIR luminosity is due to dust heating by the central AGN; heating due to stellar radiation provides a necessary but not dominant component to the emission at 20 - 60 micron. We also find that the required stellar luminosity can only be achieved if the host galaxy is able to sustain a star formation rate of ~ 1000 Msun/yr at 6.4 < z < 8 through efficient merger-driven bursts; even if all the stars were formed in this last burst of ~200 Myr of star formation, this inevitably leads to a final stellar mass that exceeds the limits imposed by dynamical mass measurements for SDSSJ1148+5251, Mdyn ~ 5.5 x 10^{10} Msun; moreover, a larger stellar mass in the range [2.3 - 4.6] x 10^{11} Msun is also required to reproduce the observed dust mass if the stars form with a standard Salpeter-like initial mass function. We discuss the implications of these results for the more general population of high-z quasars, which also show large dust masses and relatively under-massive stellar bulges.",
      "comment": "Submitted to MNRAS in the present form on October 4th 2013. Still waiting for the first referee report. Comments are welcome",
      "journal": null,
      "doi": null
    },
    {
      "version": "v3",
      "updated": "2015-05-05T13:33:03.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "spectral energy distribution",
      "standard salpeter-like initial mass function",
      "central source",
      "star formation",
      "host galaxy"
    ],
    "publication": {
      "doi": "10.1051/0004-6361/201526105",
      "journal": "Astronomy and Astrophysics",
      "year": 2015,
      "month": "Jul",
      "volume": 579
    },
    "note": {
      "typesetting": "TeX",
      "pages": 11,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 1280875,
      "adsabs": "2015A&A...579A..60S"
    }
  }
}