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Description
This table contains an all-sky sample of ~1.4 million active galactic nuclei (AGNs) meeting a two-color infrared photometric selection criterion for AGNs as applied to sources from the Wide-field Infrared Survey Explorer final catalog release (AllWISE). The authors assess the spatial distribution and optical properties of their sample and find that the results are consistent with expectations for AGNs. These sources have a mean density of ~38 AGNs per square degree on the sky, and their apparent magnitude distribution peaks at g ~ 20, extending to objects as faint as g ~ 26. The authors test the AGN selection criterion against a large sample of optically identified stars and determine the "leakage" (that is, the probability that a star detected in an optical survey will be misidentified as a quasi-stellar object (QSO) in their sample) rate to be <= 4.0 x 10<sup>-5</sup>. They conclude that their sample contains almost no optically identified stars (<= 0.041%), making this sample highly promising for future celestial reference frame work as it significantly increases the number of all-sky, compact extragalactic objects. The authors further compare their sample to catalogs of known AGNs/QSOs and find a completeness value of >= 84% (that is, the probability of correctly identifying a known AGN/QSO is at least 84%) for AGNs brighter than a limiting magnitude of R <= 19. This sample includes approximately 1.1 million previously uncataloged AGNs. The WISE survey is an all-sky mid-IR survey at 3.4, 4.6, 12, and 22 microns (W1, W2, W3, and W4, respectively) conducted between 2010 January 7 and August 6, during the cryogenic mission phase, and first made available to the public on 2011 April 14. WISE has angular resolutions of 6.1, 6.4, 6.5, and 12.0 arcseconds in its four bands, respectively. The AllWISE data release, which was used for this work, incorporates data from the WISE Full Cryogenic, 3-Band Cryo, and NEOWISE Post-Cryo survey (Mainzer et al. 2014, ApJ, 792, 30) phases, which were co-added to achieve a depth of coverage ~0.4 mag deeper than previous data releases. AllWISE contains the positions, apparent motions, magnitudes, and point-spread function (PSF)-profile fit information for almost 748 million objects. Astrometric calibration of sources in the WISE catalog was done by correlation with bright stars from the 2MASS point source catalog, and the astrometric accuracy for sources in the AllWISE release was further improved by taking into account the proper motions of these reference stars, taken from the fourth USNO CCD Astrograph Catalog (UCAC4, Zacharias et al. 2013, AJ, 145, 44). A comparison with ICRF sources shows that AllWISE Catalog sources in the brightness range of 8 < W1 < 12 mag have positional accuracies to within 50 mas, and half of these sources have positional accuracies to within 20 mas. For more details on the WISE mission, see Wright et al. (2010, AJ, 140, 1868). The authors took all sources from the AllWISE catalog following Equations (3) and (4) from Mateos et al. (2012, MNRAS, 426, 3271) and they require that all of their sources have S/N >= 5 in the first three bands, as recommended in Mateos et al. (2012); as a further constraint, they limit their results to those with cc_flags = "0000," meaning that the sources are unaffected by known artifacts such as diffraction spikes, persistence, halos, or optical ghosts. In order to characterize the optical properties of their sample, the authors cross-matched it to SDSS-DR12, which is the final data release of SDSS-III (Eisenstein et al. 2011, AJ, 142, 72), within a radial tolerance of R < 1", obtaining 424,366 matches. To determine the fraction of false positive positional matches (that is, incorrectly correlating an object in their sample with a different SDSS object due to random positional agreement), they performed the same match on a scrambled version of their sample coordinates, determining that less than 1% of other cross-matches are false positive positional matches between the two catalogs. The authors also cross-matched their sample sources with he second release of the Large Quasar Astrometric Catalog (LQAC-2; Souchay et al. 2012, A&A, 537, A99), which contains 187,504 quasars, including radio-selected quasars from the ICRF2, optically selected quasars from SDSS, and infrared-selected quasars from 2MASS, and thus represents a robust sample of quasars over a wide range of wavelengths. They find that 93,403 quasars from LQAC-2 have clean detections. The majority of non-detections are due to sources in LQAC-2 that are too faint, having R >~ 19. This table was created by the HEASARC in January 2016 based on the machine-readable version of Table 1 from the reference paper which was obtained from the ApJS web site. This is a service provided by NASA HEASARC .
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