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Published February 20, 2011 | Published
Journal Article Open

Probing the Faint End of the Quasar Luminosity Function at z~4 in the COSMOS Field


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 (QLF). 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 eight low-luminosity quasars at z ~ 4. In order to derive the 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 (β = −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.

Additional Information

© 2011 American Astronomical Society. Received 2010 November 9; accepted 2010 December 20; published 2011 January 25. We thank the Subaru staff for their invaluable help and all members of the COSMOS team. T.M., K.M., and Y.I. are financially supported by the Japan Society for the Promotion of Science (JSPS) through the JSPS Research Fellowship.

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Published - Ikeda2011p13025Astrophys_J_Lett.pdf


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