Far-IR emission from bright high-redshift quasars

Abstract The majority of quasars detected at high redshifts ( z ≳ 6 z\gtrsim 6 ) strongly emit ultraviolet radiation with absolute magnitudes at rest-frame M 1450 Å , A B ∼ − ( 29 – 27 ) {M}_{1450\mathring{\rm A} ,AB}\hspace{0.33em} \sim \hspace{0.33em}-\left(29\hspace{0.1em}\text{–}\hspace{0.1em}27) . Some of them have high luminosities in [CII] 158 μ m 158\hspace{0.33em}{\rm{\mu }}{\rm{m}} 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] 158 μ m 158\hspace{0.33em}{\rm{\mu }}{\rm{m}} 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] 158 μ m 158\hspace{0.33em}{\rm{\mu }}{\rm{m}} line and the underlying FIR continuum to reproduce the [CII]-FIR ratio observed in high-redshift quasars for a reasonable SMBH mass of M • ∼ 1 0 9 M ⊙ {M}_{\bullet }\hspace{0.33em} \sim \hspace{0.33em}1{0}^{9}{M}_{\odot } . 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.