1997/10/27 by C. R. Benn, Chris Benn, M. Vigotti +5 · 47 citations
Physics and Astronomy · #Astronomy #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Astrophysics #Galaxies: Formation, Evolution, Phenomena #Galaxy #Infrared #Infrared excess #Luminous infrared galaxy #Physics #Population #QSOS #Quasar #Stars #astro-ph
paper · pdf · doi:10.1046/j.1365-8711.1998.t01-2-01327.x
published in Monthly Notices of the Royal Astronomical Society 295(2), 451-456 (Oxford University Press) · 16 pages TeX file + 2 PostScript figures. Accepted in MNRAS
arxiv created 1997/10/27 · openalex publication_date 1998/04/01 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
Webster et al. claimed that up to 80 per cent of QSOs may be obscured by dust. They inferred the presence of this dust from the remarkably broad range of B−K optical–infrared colours of a sample of flat-spectrum PKS radio QSOs. If such dust is typical of QSOs, it will have rendered invisible most of those which would otherwise have been detected by optical surveys. We used the William Herschel Telescope on La Palma to obtain K infrared images of 54 B3 radio QSOs selected at low frequency (mainly steep-spectrum), and we find that although several have very red optical–infrared colours, most of these can be attributed to an excess of light in K rather than a dust-induced deficit in B. We present evidence that some of the infrared excess comes from the light of stars in the host galaxy (some, as previously suggested, comes from synchrotron radiation associated with flat-spectrum radio sources). The B−K colours of the B3 QSOs provide no evidence for a large reddened population. Either the Webster et al. QSOs are atypical in having such large extinctions, or their reddening is not due to dust; either way, the broad range of their B−K colours does not provide evidence that a large fraction of QSOs has been missed from optical surveys.