Issue |
A&A
Volume 505, Number 1, October I 2009
|
|
---|---|---|
Page(s) | 97 - 104 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361/200811161 | |
Published online | 22 June 2009 |
Discovery of a redshift 6.13 quasar in the UKIRT infrared deep sky survey
1
Astrophysics Group, Imperial College London, Blackett Laboratory, Prince Consort Road, London, SW7 2AZ, UK e-mail: mortlock@ic.ac.uk
2
Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA, UK
3
Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead, CH41 1LD, UK
4
Anglo Australian Observatory, PO Box 296, Epping, NSW 1710, Australia
5
Centre for Astrophysics Research, Science and Technology Research Institute, University of Hertfordshire, Hatfield, AL10 9AB, UK
6
School of Physics & Astronomy, Queens Building, Cardiff University, The Parade, Cardiff CF24 3AA, UK
7
Institute of Astronomy, School of Physics, The University of Sydney, NSW 2006, Australia
8
Laboratorio de Astrofísica Espacial y Física Fundamental, European Space Astronomy Center, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain
Received:
15
October
2008
Accepted:
17
April
2009
Optical and near-infrared (NIR) spectra are presented for
ULAS J131911.29+095051.4 (hereafter ULAS J1319+0950), a new redshift z = 6.127
± 0.004 quasar discovered in the Third Data Release (DR3) of the
UKIRT Infrared Deep Sky Survey (UKIDSS).
The source has = 19.10 ± 0.03, corresponding to
=
-27.12, which is comparable to the absolute magnitudes of the
z
6 quasars discovered in the Sloan Digital Sky Survey (SDSS).
ULAS J1319+0950 was, in
fact, registered by SDSS as a faint source with
=
20.13 ± 0.12, just below the signal-to-noise ratio limit of the
SDSS high-redshift quasar survey. The faint z-band magnitude is a
consequence of the weak Ly α/N v emission line, which has a
rest-frame equivalent width of ~20Å and
provides only a small boost to the z-band flux. Nevertheless,
there is no evidence of a significant new population of high-redshift
quasars with weak emission lines from this UKIDSS-based search.
The Ly α optical depth to ULAS J1319+0950 is consistent with that measured
towards similarly distant SDSS quasars, implying that results from
optical- and NIR-selected quasars may be combined in studies of
cosmological reionization.
Also presented is a new NIR-spectrum of the previously discovered UKIDSS
quasar ULAS J020332.38+001229.2, which reveals the object to be a broad
absorption line quasar. The new spectrum shows that the emission
line initially identified as Ly α is actually N v, leading to a
revised redshift of z = 5.72, rather than z = 5.86 as
previously estimated.
Key words: galaxies: quasars: individual: ULAS J020332.38+001229.2, ULAS J131911.29+095051.4 / infrared: general / cosmology: observations
© ESO, 2009
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