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arXiv · 1011.2280

Probing the faint end of the quasar luminosity function at z ~ 4 in the COSMOS field

H. Ikeda·T. Nagao·K. Matsuoka·Y. Taniguchi·Y. Shioya·J. R. Trump·P. Capak·A. Comastri·M. Enoki·Y. Ideue·Y. Kakazu·A. M. Koekemoer·T. Morokuma·T. Murayama·T. Saito·M. Salvato·E. Schinnerer·N. Z. Scoville·J. D. Silverman
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Abstract

We searched for quasars that are ~ 3 mag fainter than the SDSS quasars in the redshift range 3.7 < z < 4.7 in the COSMOS field to constrain the faint end of the quasar luminosity function. Using optical photometric data, we selected 31 quasar candidates with 22 < i' < 24 at z ~ 4. We obtained optical spectra for most of these candidates using FOCAS on the Subaru telescope, and identified 8 low-luminosity quasars at z ~ 4. In order to derive the quasar luminosity function (QLF) based on our spectroscopic follow-up campaign, we estimated the photometric completeness of our quasar survey through detailed Monte Carlo simulations. Our QLF at z ~ 4 has a much shallower faint-end slope beta = -1.67^{+0.11}_{-0.17} than that obtained by other recent surveys in the same redshift. Our result is consistent with the scenario of downsizing evolution of active galactic nuclei inferred by recent optical and X-ray quasar surveys at lower redshifts.

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H. Ikeda, T. Nagao, K. Matsuoka, Y. Taniguchi, Y. Shioya, J. R. Trump, P. Capak, A. Comastri, M. Enoki, Y. Ideue, Y. Kakazu, A. M. Koekemoer, T. Morokuma, T. Murayama, T. Saito, M. Salvato, E. Schinnerer, N. Z. Scoville, J. D. Silverman. 2010-11-10. Probing the faint end of the quasar luminosity function at z ~ 4 in the COSMOS field. https://doi.org/10.1088/2041-8205/728/2/l25

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