| Issue |
A&A
Volume 411, Number 3, December I 2003
|
|
|---|---|---|
| Page(s) | 343 - 350 | |
| Section | Extragalactic astronomy | |
| DOI | https://doi.org/10.1051/0004-6361:20031291 | |
| Published online | 17 November 2003 | |
A submillimetre selected quasar in the field of Abell 478*
Leiden Observatory, PO Box 9513, 2300 RA Leiden, The Netherlands e-mail: [kraiberg,pvdwerf,jaffe]@strw.leidenuniv.nl
Corresponding author: K. K. Knudsen, kraiberg@strw.leidenuniv.nl
Received:
4
June
2003
Accepted:
21
August
2003
We present the discovery of a dusty quasar, SMM J04135+10277,
located behind the
galaxy cluster Abell 478. The quasar was discovered as the
brightest source in a submillimetre
survey of high redshift galaxies lensed by foreground
rich clusters of galaxies in a project aimed at studying the cosmic star
formation history of dusty galaxies. With
submillimetre fluxes of
and 
this object is one of the brightest submillimetre sources known.
Optical imaging revealed a point source with
(corrected for galactic extinction). Follow-up
optical spectroscopy showed this object to be a quasar at
redshift 
.
The quasar was also detected at shorter infrared wavelengths
with the Infrared Space Observatory.
This object is the first quasar discovered by its submillimetre
emission. Given the general lack of overlap between deep submillimetre
and X-ray samples, usually interpreted as a low incidence of active nuclei in
submillimetre samples, this is an unusual object. Analysis of number
counts of quasars and of submillimetre galaxies bears out this suggestion.
We compare the properties of SMM J04135+10277 to those
of optically selected quasars with submillimetre emission, and argue
that the optical faintness results from a large viewing angle with the
direction of relativistic beaming, and not from abnormally high
extinction. We also find indications that the bulk of the submillimetre
flux density is not powered by the quasar nucleus. This conclusion is
supported by analysis of the infrared spectral energy distribution.
These results are consistent with previous
observations that quasars at
higher redshift tend to have a more prominent cold dust component, most
likely powered by extended star formation in the host galaxy.
The temperature for the cold dust component is found be 
when assuming 
for a modified blackbody.
The quasar is found to have a total infrared luminosity of 
, dominated by the emission from cool dust.
Key words: quasars: individual: SMM J04135+10277 / infrared: galaxies
Based on observations made with ESO Telescopes at the Paranal Observatory under programme IDs 63.O-0087 and 68.A-0111. Also based on observations with ISO, an ESA project with instruments funded by ESA member states (especially the PI countries: the Netherlands, the United Kingdom, Germany, and France) with the participation of ISAS and NASA.
© ESO, 2003
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