Far-IR emission from bright high-redshift quasars

Abstract

The majority of quasars detected at high redshifts ( z≳6 ) strongly emit ultraviolet radiation with absolute magnitudes at rest-frame M1450Å,AB∼−(29–27) . Some of them have high luminosities in [CII] 158μm line and in far-infrared (FIR) continuum, which leads to the expectation of a large amount of much cold dusty gas in these quasars. We have studied the relation between luminosities in the [CII] 158μm and the FIR continuum for a slightly absorbed supermassive black hole (SMBH) obscured by an ensemble of dense clouds with a low covering factor. We have found that dense clouds with a low covering factor can give sufficient luminosities in [CII] 158μm line and the underlying FIR continuum to reproduce the [CII]-FIR ratio observed in high-redshift quasars for a reasonable SMBH mass of M∙∼109M⊙ . We note that many distant mildly/heavily obscured active galactic nuclei are to avoid detection in near-infrared (IR) wavelengths; if this is the case, blind IR/FIR surveys are needed.