Dusty Gas Accretion onto Massive Black Holes and Infrared Diagnosis of the Eddington Ratio

Hidenobu Yajima, Massimo Ricotti, Kwangho Park, Kazuyuki Sugimura

Research output: Contribution to journalArticlepeer-review

6 Citations (Scopus)

Abstract

Evidence for dust around supermassive black holes (SMBHs) in the early universe is strongly suggested by recent observations. However, the accretion mechanism of SMBHs in dusty gas is not well understood yet. We investigate the growth of intermediate-mass black holes (IMBHs) of ∼104 10 6 - M· in dusty clouds by using onedimensional radiative-hydrodynamics simulations. We find that the accretion of dusty gas onto IMBHs proceeds gently with small fluctuations of the accretion rate, whereas that of pristine gas causes more violent periodic bursts. At dust-to-gas mass ratios similar to the solar neighborhood, the time-averaged luminosity becomes smaller than that for primordial gas by one order of magnitude and the time-averaged Eddington ratio ranges from ∼10-4 to ∼10-2 in clouds with initial gas densities of nH = 10 1000 cm - -3. Our calculations show that the effect of dust opacity alone is secondary compared to the radiation pressure on dust in regulating the BH growth. We also derive spectral energy distributions at IR bands by calculating dust thermal emission and show that the flux ratio between l ≲ 20 mm and ≳100 mm is closely related to the Eddington ratio. Thermal emission from hot dust near the BH dominates only during the phase of high accretion, producing higher flux density at ≲20 mm. Therefore, we suggest that a combination of mid-IR observations by the James Webb Space Telescope and far-IR observations by ALMA or Spitzer can be used to estimate the Eddington ratio of massive BHs. We also extend our simple modeling to SMBHs of 108 109 - M· and show that ALMA can detect SMBHs of ∼109 M· at z ≳ 5.

Original languageEnglish
Article number3
JournalAstrophysical Journal
Volume846
Issue number1
DOIs
Publication statusPublished - 2017 Sep 1

Keywords

  • dust
  • extinction
  • galaxies: evolution
  • galaxies: high-redshift
  • quasars: supermassive black holes
  • radiative transfer

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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