Far-IR emission from bright high-redshift quasars

Abstract

The majority of quasars detected at high redshifts (z≳6z\gtrsim 6) strongly emit ultraviolet radiation with absolute magnitudes at rest-frame M1450Å,AB∼−(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] 158μm158\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] 158μm158\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] 158μm158\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•∼109M⊙{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.

Keywords

• early universe – galaxies: high-redshift – quasars: supermassive black holes – interstellar medium: dust
• extinction – ultraviolet: galaxies – infrared: galaxies