paper

An Unbiassed Census of Active Galactic Nuclei in the Two Micron All Sky Survey

arXiv:astro-ph/0310396 · doi:10.1086/380939

Abstract

(Abridged) We present an unbiassed near-IR selected AGN sample, covering 12.56 square degrees down to K ~ 15.5, selected from the Two Micron All Sky Survey (2MASS). Our only selection effect is a moderate color cut (J-K>1.2) designed to reduce contamination from galactic stars. We observed both point-like and extended sources. Using the brute-force capabilities of the 2dF multi-fiber spectrograph on the Anglo-Australian Telescope, we obtained spectra of 65% of the target list: an unbiassed sub-sample of 1526 sources. 80% of the 2MASS sources in our fields are galaxies, with a median redshift of 0.15. The remainder are K- and M-dwarf stars. Seyfert-2 Galaxies are roughly three times more common in this sample than in optically selected galaxy samples (once corrections have been made for the equivalent width limit and for different aperture sizes). We find 14 broad-line (Type-1) AGNs, giving a surface density down to K<15 comparable to that of optical samples down to B=18.5. Half of our Type-1 AGNs could not have been found by normal color selection techniques. In all cases this was due host galaxy light contamination rather than intrinsically red colors. We conclude that the Type-1 AGN population found in the near-IR is not dramatically different from that found in optical samples. There is no evidence for a large population of AGNs that could not be found at optical wavelengths, though we can only place very weak constraints on any population of dusty high-redshift QSOs.

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