Volume 627, July 2019
|Number of page(s)||13|
|Published online||27 June 2019|
Millennium Institute of Astrophysics (MAS), Nuncio Monseñor Sotero Sanz 100, Providencia, Santiago, Chile
e-mail: email@example.com; firstname.lastname@example.org
2 Instituto de Astrofísica, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 7820436 Macul, Santiago, Chile
3 Department of Physics, University of Napoli “Federico II”, Via Cinthia 9, 80126 Napoli, Italy
4 INFN – Sezione di Napoli, Via Cinthia 9, 80126 Napoli, Italy
5 INAF – Osservatorio Astronomico di Capodimonte, Via Moiariello 16, 80131 Napoli, Italy
6 KTH Royal Institute of Technology, Brinellvägen 8, 114 28 Stockholm, Sweden
7 Institut für Astro- und Teilchenphysik, Universität Innsbruck, Technikerstraße 25/8, Innsbruck 6020, Austria
8 Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802, USA
9 Institute for Gravitation and the Cosmos, The Pennsylvania State University, University Park, PA 16802, USA
10 Space Science Institute, 4750 Walnut Street, Suite 2015, Boulder, CO 80301, USA
11 Department of Physics, University of Roma “Tor Vergata”, Via della Ricerca Scientifica 1, 00133 Roma, Italy
12 Departamento de Ciencias Fisicas, Universidad Andres Bello, Avda. Republica 252, Santiago, Chile
13 Department of Physics and Astronomy, University of the Western Cape, Private Bag X17, 7535 Bellville, Cape Town, South Africa
14 INAF – Istituto di Radioastronomia, Via Gobetti 101, 40129 Bologna, Italy
15 INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
16 Max Planck Institut für Extraterrestrische Physik, Giessenbachstraße 1, 85748 Garching bei München, Germany
17 School of Physics and Astronomy, Sun Yat-sen University, Zhuhai Campus, Guangzhou 519082, PR China
18 Department of Astronomy, University of Cape Town, Private Bag X3, Rondebosch 7701 Cape Town, South Africa
Accepted: 22 May 2019
Context. The analysis of the variability of active galactic nuclei (AGN) at different wavelengths and the study of possible correlations of different spectral windows are a current main field of inquiry. Optical variability has been largely used to identify AGN in multivisit surveys. The strength of a selection based on optical variability lies in the opportunity of analyzing data from surveys of large sky areas by ground-based telescopes. However, the effectiveness of optical variability selection with respect to other multiwavelength techniques has been poorly studied down to the depth that is expected from next-generation surveys.
Aims. Here we present the results of our r-band analysis of a sample of 299 optically variable AGN candidates in the VST survey of the COSMOS field, counting 54 visits spread over three observing seasons spanning more than three years. This dataset is more than three times larger than the dataset presented in our previous analysis, and the observing baseline is about eight times longer.
Methods. We push toward deeper magnitudes (r(AB) ∼ 23.5 mag) than were reached in past studies. We made wide use of ancillary multiwavelength catalogs in order to confirm the nature of our AGN candidates, and constrained the accuracy of the method based on spectroscopic and photometric diagnostics. We also performed tests aimed at assessing the relevance of dense sampling in view of future wide-field surveys.
Results. We demonstrate that the method allows the selection of high-purity (> 86%) samples. We take advantage of the longer observing baseline to achieve great improvement in the completeness of our sample with respect to X-ray and spectroscopically confirmed samples of AGN (59% vs. ∼15% in our previous work), as well as in the completeness of unobscured and obscured AGN. The effectiveness of the method confirms the importance of developing future more refined techniques for the automated analysis of larger datasets.
Key words: galaxies: active / quasars: general / X-rays: galaxies / surveys
Table 3 is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (126.96.36.199) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/627/A33.
© ESO 2019
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