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Title: DISCOVERING THE MISSING 2.2 < z < 3 QUASARS BY COMBINING OPTICAL VARIABILITY AND OPTICAL/NEAR-INFRARED COLORS

Abstract

The identification of quasars in the redshift range 2.2 < z < 3 is known to be very inefficient because the optical colors of such quasars are indistinguishable from those of stars. Recent studies have proposed using optical variability or near-infrared (near-IR) colors to improve the identification of the missing quasars in this redshift range. Here we present a case study combining both methods. We select a sample of 70 quasar candidates from variables in Sloan Digital Sky Survey (SDSS) Stripe 82, which are non-ultraviolet excess sources and have UKIDSS near-IR public data. They are clearly separated into two parts on the Y - K/g - z color-color diagram, and 59 of them meet or lie close to a newly proposed Y - K/g - z selection criterion for z < 4 quasars. Of these 59 sources, 44 were previously identified as quasars in SDSS DR7, and 35 of them are quasars at 2.2 < z < 3. We present spectroscopic observations of 14 of 15 remaining quasar candidates using the Bok 2.3 m telescope and the MMT 6.5 m telescope, and successfully identify all of them as new quasars at z = 2.36-2.88. We also apply this method tomore » a sample of 643 variable quasar candidates with SDSS-UKIDSS nine-band photometric data selected from 1875 new quasar candidates in SDSS Stripe 82 given by Butler and Bloom based on the time-series selections, and find that 188 of them are probably new quasars with photometric redshifts at 2.2 < z < 3. Our results indicate that the combination of optical variability and optical/near-IR colors is probably the most efficient way to find 2.2 < z < 3 quasars and is very helpful for constructing a complete quasar sample. We discuss its implications for ongoing and upcoming large optical and near-IR sky surveys.« less

Authors:
 [1]; ; ; ;  [2];  [3]
  1. Department of Astronomy, School of Physics, Peking University, Beijing 100871 (China)
  2. Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States)
  3. Max Planck Institut fuer Astronomie, Koenigstuhl 17, D-69117 Heidelberg (Germany)
Publication Date:
OSTI Identifier:
21582924
Resource Type:
Journal Article
Journal Name:
Astronomical Journal (New York, N.Y. Online)
Additional Journal Information:
Journal Volume: 142; Journal Issue: 3; Other Information: DOI: 10.1088/0004-6256/142/3/78; Journal ID: ISSN 1538-3881
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; COLOR MODEL; RED SHIFT; STARS; TELESCOPES; ULTRAVIOLET RADIATION; COMPOSITE MODELS; ELECTROMAGNETIC RADIATION; MATHEMATICAL MODELS; PARTICLE MODELS; QUARK MODEL; RADIATIONS

Citation Formats

Wu Xuebing, Wang Ran, Bian Fuyan, Jiang Linhua, Fan Xiaohui, and Schmidt, Kasper B., E-mail: wuxb@bac.pku.edu.cn. DISCOVERING THE MISSING 2.2 < z < 3 QUASARS BY COMBINING OPTICAL VARIABILITY AND OPTICAL/NEAR-INFRARED COLORS. United States: N. p., 2011. Web. doi:10.1088/0004-6256/142/3/78.
Wu Xuebing, Wang Ran, Bian Fuyan, Jiang Linhua, Fan Xiaohui, & Schmidt, Kasper B., E-mail: wuxb@bac.pku.edu.cn. DISCOVERING THE MISSING 2.2 < z < 3 QUASARS BY COMBINING OPTICAL VARIABILITY AND OPTICAL/NEAR-INFRARED COLORS. United States. doi:10.1088/0004-6256/142/3/78.
Wu Xuebing, Wang Ran, Bian Fuyan, Jiang Linhua, Fan Xiaohui, and Schmidt, Kasper B., E-mail: wuxb@bac.pku.edu.cn. Thu . "DISCOVERING THE MISSING 2.2 < z < 3 QUASARS BY COMBINING OPTICAL VARIABILITY AND OPTICAL/NEAR-INFRARED COLORS". United States. doi:10.1088/0004-6256/142/3/78.
@article{osti_21582924,
title = {DISCOVERING THE MISSING 2.2 < z < 3 QUASARS BY COMBINING OPTICAL VARIABILITY AND OPTICAL/NEAR-INFRARED COLORS},
author = {Wu Xuebing and Wang Ran and Bian Fuyan and Jiang Linhua and Fan Xiaohui and Schmidt, Kasper B., E-mail: wuxb@bac.pku.edu.cn},
abstractNote = {The identification of quasars in the redshift range 2.2 < z < 3 is known to be very inefficient because the optical colors of such quasars are indistinguishable from those of stars. Recent studies have proposed using optical variability or near-infrared (near-IR) colors to improve the identification of the missing quasars in this redshift range. Here we present a case study combining both methods. We select a sample of 70 quasar candidates from variables in Sloan Digital Sky Survey (SDSS) Stripe 82, which are non-ultraviolet excess sources and have UKIDSS near-IR public data. They are clearly separated into two parts on the Y - K/g - z color-color diagram, and 59 of them meet or lie close to a newly proposed Y - K/g - z selection criterion for z < 4 quasars. Of these 59 sources, 44 were previously identified as quasars in SDSS DR7, and 35 of them are quasars at 2.2 < z < 3. We present spectroscopic observations of 14 of 15 remaining quasar candidates using the Bok 2.3 m telescope and the MMT 6.5 m telescope, and successfully identify all of them as new quasars at z = 2.36-2.88. We also apply this method to a sample of 643 variable quasar candidates with SDSS-UKIDSS nine-band photometric data selected from 1875 new quasar candidates in SDSS Stripe 82 given by Butler and Bloom based on the time-series selections, and find that 188 of them are probably new quasars with photometric redshifts at 2.2 < z < 3. Our results indicate that the combination of optical variability and optical/near-IR colors is probably the most efficient way to find 2.2 < z < 3 quasars and is very helpful for constructing a complete quasar sample. We discuss its implications for ongoing and upcoming large optical and near-IR sky surveys.},
doi = {10.1088/0004-6256/142/3/78},
journal = {Astronomical Journal (New York, N.Y. Online)},
issn = {1538-3881},
number = 3,
volume = 142,
place = {United States},
year = {2011},
month = {9}
}