J/MNRAS/406/1583 Quasar from SDSS and UKIDSS (Wu+, 2010)
Quasar candidate selection and photometric redshift estimation based on SDSS
and UKIDSS data.
Wu X.-B., Jia Z.
<Mon. Not. R. Astron. Soc., 406, 1583-1594 (2010)>
=2010MNRAS.406.1583W 2010MNRAS.406.1583W
ADC_Keywords: Surveys ; QSOs ; Redshifts ; Photometry, SDSS ;
Photometry, infrared
Keywords: catalogues - surveys - quasars: emission lines - quasars: general
Abstract:
We present a sample of 8498 quasars with both Sloan Digital Sky Survey
(SDSS) ugriz optical and United Kingdom Infrared Telescope (UKIRT)
Infrared Deep Sky Survey (UKIDSS) YJHK near-infrared (near-IR)
photometric data. With this sample, we obtain the median colour-z
relations based on 7400 quasars with magnitude uncertainties less than
0.1mag in all bands. By analysing the quasar colours, we propose an
empirical criterion in the Y-K versus g-z colour-colour diagram
to separate stars and quasars with redshift z<4, and two other
criteria for selecting high-redshift quasars. Using the SDSS-UKIDSS
colour-z relations, we estimate the photometric redshifts of 8498
SDSS-UKIDSS quasars, and find that 85.0 per cent of them are
consistent with the spectroscopic redshifts within |Δz|<0.2, which
leads to a significant increase of the photometric redshift accuracy
from that based on the SDSS colour-z relations only. As two tests,
we compare our colour-selection criterion with a small UKIDSS/EDR
quasar/star sample and a sample of 4671 variable sources in the SDSS
Stripe 82 region with both SDSS and UKIDSS data. We find that they can
be clearly divided into two classes (quasars and stars) by our
criterion in the Y-K versus g-z plot.
Description:
We cross-identify all quasars in SDSS Data Release 7 (DR7) with the
UKIDSS DR3, by finding the closest counterparts within 3-arcsec
between the positions in two surveys and requesting all detections in
both SDSS ugriz and UKIDSS YJHK bands for each quasar. To do the
cross-identifications, we use the CrossID form available at the UKIDSS
WFCAM Science Archive web site
(http://surveys.roe.ac.uk:8080/wsa/crossID_form.jsp/) and use only the
data in UKIDSS Large Area Survey (LAS) in order to avoid the
misidentifications in the crowded fields with lower Galactic
latitudes. This results in a sample of 8498 quasars with both SDSS and
UKIDSS data.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 91 8498 Parameters of 8498 SDSS-UKIDSS quasars
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See also:
http://www.sdss.org : SDSS Home Page
http://www.ukidss.org : UKIDSS Home Page
http://surveys.roe.ac.uk/wsa/theSurveys.html : UKIDSS
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 11 F11.7 deg RAdeg SDSS right ascension (J2000)
13- 22 F10.7 deg DEdeg SDSS declination (J2000)
24- 28 F5.3 --- z Redshift (from SDSS)
30- 34 F5.3 arcsec Offset SDSS-UKIDSS offset
36- 41 F6.2 mag umag ?=-99.99 SDSS u magnitude (Vega system)
43- 48 F6.2 mag gmag ?=-99.99 SDSS g magnitude (Vega system)
50- 54 F5.2 mag rmag SDSS r magnitude (Vega system)
56- 60 F5.2 mag imag SDSS i magnitude (Vega system)
62- 67 F6.2 mag zmag ?=-99.99 SDSS z magnitude (Vega system)
69- 73 F5.2 mag Ymag UKIDSS Y magnitude (Vega system)
75- 79 F5.2 mag Jmag UKIDSS J magnitude (Vega system)
81- 85 F5.2 mag Hmag UKIDSS H magnitude (Vega system)
87- 91 F5.2 mag Kmag UKIDSS K magnitude (Vega system)
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 01-Feb-2011