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|Title:||Variability-selected active galactic nuclei in the VST-SUDARE/VOICE survey of the COSMOS field||Authors:||De Cicco, D.
BOTTICELLA, MARIA TERESA
Brandt, W. N.
NAPOLITANO, NICOLA ROSARIO
|Issue Date:||2015||Journal:||ASTRONOMY & ASTROPHYSICS||Number:||574||First Page:||1||Abstract:||Context. Active galaxies are characterized by variability at every wavelength, with timescales from hours to years depending on the observing window. Optical variability has proven to be an effective way of detecting AGNs in imaging surveys, lasting from weeks to years. <BR /> Aims: In the present work we test the use of optical variability as a tool to identify active galactic nuclei in the VST multiepoch survey of the COSMOS field, originally tailored to detect supernova events. <BR /> Methods: We make use of the multiwavelength data provided by other COSMOS surveys to discuss the reliability of the method and the nature of our AGN candidates. <BR /> Results: The selection on the basis of optical variability returns a sample of 83 AGN candidates; based on a number of diagnostics, we conclude that 67 of them are confirmed AGNs (81% purity), 12 are classified as supernovae, while the nature of the remaining 4 is unknown. For the subsample of AGNs with some spectroscopic classification, we find that Type 1 are prevalent (89%) compared to Type 2 AGNs (11%). Overall, our approach is able to retrieve on average 15% of all AGNs in the field identified by means of spectroscopic or X-ray classification, with a strong dependence on the source apparent magnitude (completeness ranging from 26% to 5%). In particular, the completeness for Type 1 AGNs is 25%, while it drops to 6% for Type 2 AGNs. The rest of the X-ray selected AGN population presents on average a larger rms variability than the bulk of non-variable sources, indicating that variability detection for at least some of these objects is prevented only by the photometric accuracy of the data. The low completeness is in part due to the short observing span: we show that increasing the temporal baseline results in larger samples as expected for sources with a red-noise power spectrum. Our results allow us to assess the usefulness of this AGN selection technique in view of future wide-field surveys. <P />Observations were provided by the ESO programs 088.D-0370 and 088.D-4013 (PI G. Pignata).Table 3 is available in electronic form at <A href="http://www.aanda.org/10.1051/0004-6361/201424906/olm">http://www.aanda.org||Acknowledgments:||This work was supported by the PRIN-INAF “Galaxy Evolution with the VLT Surveys Telescope (VST)” (PI A. Grado). Funding for SDSS-III has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, and the US Department of Energy Office of Science. The SDSS-III web site is http://www.sdss3.org/ . SDSS-III is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS-III Collaboration including the University of Arizona, the Brazilian Participation Group, Brookhaven National Laboratory, University of Cambridge, Carnegie Mellon University, University of Florida, the French Participation Group, the German Participation Group, Harvard University, the Instituto de Astrofisica de Canarias, the Michigan State/Notre Dame/JINA Participation Group, Johns Hopkins University, Lawrence Berkeley National Laboratory, Max Planck Institute for Astrophysics, Max Planck Institute for Extraterrestrial Physics, New Mexico State University, New York University, Ohio State University, Pennsylvania State University, University of Portsmouth, Princeton University, the Spanish Participation Group, University of Tokyo, University of Utah, Vanderbilt University, University of Virginia, University of Washington, and Yale University. G.P. acknowledges support provided by the Millennium Institute of Astrophysics through grant IC120009 of the Programa Iniciativa Cientifica Milenio del Ministerio de Economia, Fomento y Turismo de Chile. M.V. acknowledges funding from the Square Kilometre Array South Africa project and from the South African National Research Foundation. We thank Marcella Brusa, Francesca Civano, and Stefano Marchesi for providing access to updated versions of the COSMOS catalogs. We also thank the anonymous referee for helpful comments and suggestions.||URI:||http://hdl.handle.net/20.500.12386/23583||URL:||https://www.aanda.org/articles/aa/abs/2015/02/aa24906-14/aa24906-14.html||ISSN:||0004-6361||DOI:||10.1051/0004-6361/201424906||Bibcode ADS:||2015A&A...574A.112D||Fulltext:||open|
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