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Constraints on the Faint End of the Quasar Luminosity Function at z ~ 5 in the COSMOS Field

Ikeda, H. and Nagao, T. and Matsuoka, K. and Taniguchi, Y. and Shioya, Y. and Kajisawa, M. and Enoki, M. and Capak, P. and Civano, F. and Koekemoer, A. M. and Masters, D. and Morokuma, T. and Salvato, M. and Schinnerer, E. and Scoville, N. Z. (2012) Constraints on the Faint End of the Quasar Luminosity Function at z ~ 5 in the COSMOS Field. Astrophysical Journal, 756 (2). Art. No. 160. ISSN 0004-637X. http://resolver.caltech.edu/CaltechAUTHORS:20121106-101127819

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Abstract

We present the result of our low-luminosity quasar survey in the redshift range of 4.5 ≲ z ≲ 5.5 in the COSMOS field. Using the COSMOS photometric catalog, we selected 15 quasar candidates with 22 < i' < 24 at z ~ 5 that are ~3 mag fainter than the Sloan Digital Sky Survey quasars in the same redshift range. We obtained optical spectra for 14 of the 15 candidates using FOCAS on the Subaru Telescope and did not identify any low-luminosity type-1 quasars at z ~ 5, while a low-luminosity type-2 quasar at z ~ 5.07 was discovered. In order to constrain the faint end of the quasar luminosity function at z ~ 5, we calculated the 1σ confidence upper limits of the space density of type-1 quasars. As a result, the 1σ confidence upper limits on the quasar space density are Φ < 1.33 × 10^(–7) Mpc^(–3) mag^(–1) for –24.52 < M_(1450) < –23.52 and Φ < 2.88 × 10^(–7) Mpc^(–3) mag^(–1) for –23.52 < M_1450 < –22.52. The inferred 1σ confidence upper limits of the space density are then used to provide constraints on the faint-end slope and the break absolute magnitude of the quasar luminosity function at z ~ 5. We find that the quasar space density decreases gradually as a function of redshift at low luminosity (M_1450 ~ –23), being similar to the trend found for quasars with high luminosity (M_1450 < –26). This result is consistent with the so-called downsizing evolution of quasars seen at lower redshifts.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1088/0004-637X/756/2/160DOIUNSPECIFIED
http://iopscience.iop.org/0004-637X/756/2/160PublisherUNSPECIFIED
Additional Information:© 2012 American Astronomical Society. Received 2011 July 9; accepted 2012 July 6; published 2012 August 24. We thank the Subaru staff for their invaluable help and all members of the COSMOS team. This work was financially supported in part by the Japan Society for the Promotion of Science (JSPS; grant Nos. 23244031 and 23654068). This work was also partly supported by the FIRST program “Subaru Measurements of Images and Redshifts (SuMIRe),” which was initiated by the Council for Science and Technology Policy (CSTP). K.M. is financially supported by the JSPS through the JSPS Research Fellowship.
Group:COSMOS
Funders:
Funding AgencyGrant Number
Japan Society for the Promotion of Science (JSPS)23244031
Japan Society for the Promotion of Science (JSPS)23654068
Council for Science and Technology Policy (CSTP)UNSPECIFIED
Japan Society for the Promotion of Science (JSPS) Research FellowshipUNSPECIFIED
Subject Keywords:cosmology: observations; quasars: general; surveys
Record Number:CaltechAUTHORS:20121106-101127819
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20121106-101127819
Official Citation:Constraints on the Faint End of the Quasar Luminosity Function at z ~ 5 in the COSMOS Field H. Ikeda et al. 2012 ApJ 756 160
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:35297
Collection:CaltechAUTHORS
Deposited By: Jason Perez
Deposited On:06 Nov 2012 21:42
Last Modified:06 Jul 2015 17:48

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