Optically variable active galactic nuclei in the 3 yr VST survey of the COSMOS field

Abstract

The analysis of the variability of active galactic nuclei (AGNs) at different wavelengths and the study of possible correlations among different spectral windows are nowadays a major field of inquiry. Optical variability has been largely used to identify AGNs in multivisit surveys. The strength of a selection based on optical variability lies in the chance to analyze 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 expected from next generation surveys. 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 > 3 yr. This dataset is > 3 times larger in size than the one presented in our previous analysis (De Cicco et al. 2015), and the observing baseline is ~8 times longer. We push towards deeper magnitudes (r(AB) ~23.5 mag) compared to past studies; we make wide use of ancillary multiwavelength catalogs in order to confirm the nature of our AGN candidates, and constrain the accuracy of the method based on spectroscopic and photometric diagnostics. We also perform tests aimed at assessing the relevance of dense sampling in view of future wide-field surveys. 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 AGNs (59%, vs. ~15% in our previous work), as well as in the completeness of unobscured and obscured AGNs. The effectiveness of the method confirms the importance to develop future, more refined techniques for the automated analysis of larger datasets.

arXiv comment21 pages, 10 figures; accepted for publication in A&A

References in corpus (46)

• A Fundamental Relation Between Supermassive Black Holes and Their Host Galaxies
• The Demography of Massive Dark Objects in Galaxy Centres
• The Infrared Array Camera (IRAC) for the Spitzer Space Telescope
• The COSMOS2015 Catalog: Exploring the 1<z<6 Universe with half a million galaxies
• The First Release COSMOS Optical and Near-IR Data and Catalog
• The COSMOS Survey: Hubble Space Telescope / Advanced Camera for Surveys (HST/ACS) Observations and Data Processing
• Obscured and unobscured active galactic nuclei in the Spitzer Space Telescope First Look Survey
• Active Galactic Nuclei: what's in a name?
• Identifying Luminous AGN in Deep Surveys: Revised IRAC Selection Criteria
• The Chandra Deep Field-South Survey: 4 Ms Source Catalogs
• The Chandra COSMOS Legacy survey: overview and point source catalog
• COSMOS : Hubble Space Telescope Observations
• Deep Extragalactic X-ray Surveys
• Photometric redshift and classification for the XMM-COSMOS sources
• Cosmic X-ray Surveys of Distant Active Galaxies: The Demographics, Physics, and Ecology of Growing Supermassive Black Holes
• The Chandra COSMOS Legacy survey: optical/IR identifications
• Galaxy Zoo : 'Hanny's Voorwerp', a quasar light echo?
• The XMM-Newton Wide-Field Survey in the COSMOS field (XMM-COSMOS): demography and multiwavelength properties of obscured and unobscured luminous AGN
• The COSMOS-WIRCam near-infrared imaging survey: I: BzK selected passive and star forming galaxy candidates at z>1.4
• The Chandra COSMOS Survey: III. Optical and Infrared Identification of X-ray Point Sources
• XMM-Newton observation of the Lockman Hole II. Spectral analysis
• Optical spectroscopy and X-ray detections of a sample of quasars and AGN selected in the mid-infrared from two Spitzer wide-area surveys
• Finding counterparts for All-sky X-ray surveys with Nway: a Bayesian algorithm for cross-matching multiple catalogues
• Selecting Quasars by their Intrinsic Variability
• Quasar Selection Based on Photometric Variability
• VEGAS: A VST Early-type GAlaxy Survey. I. Presentation, wide-field surface photometry, and substructures in NGC 4472
• A novel variability-based method for quasar selection: evidence for a rest frame ~54 day characteristic timescale
• How are AGN Found?
• Tracing the accretion history of supermassive Black Holes through X-ray variability: results from the Chandra Deep Field-South
• Bayesian High-Redshift Quasar Classification from Optical and Mid-IR Photometry
• The Chandra Deep Field North Survey. X. X-ray Emission from Very Red Objects
• Variability of Active Galactic Nuclei from the Optical to X-ray Regions
• A new extensive catalog of optically variable AGN in the GOODS Fields and a new statistical approach to variability selection
• Variability-selected Active Galactic Nuclei in the VST-SUDARE/VOICE Survey of the COSMOS Field
• Variability-selected active galactic nuclei from supernova search in the Chandra deep field south
• Variability-based AGN selection using image subtraction in the SDSS and LSST era
• The X-ray/UV ratio in Active Galactic Nuclei: dispersion and variability
• Supernova rates from the SUDARE VST-Omegacam search II. Rates in a galaxy sample
• Variability and Multiwavelength Detected AGN in the GOODS Fields
• SUDARE-VOICE variability-selection of Active Galaxies in the Chandra Deep Field South and the SERVS/SWIRE region
• Robust Identification of Active Galactic Nuclei through HST Optical Variability in GOODS-S: Comparison with the X-ray and mid-IR Selected Samples
• Pan-STARRS1 variability of XMM-COSMOS AGN. I. Impact on photometric redshifts
• Optical Variability of Infrared Power Law-Selected Galaxies & X-ray Sources in the GOODS-South Field
• A weak lensing analysis of the Abell 383 cluster
• Spectroscopic follow-up of variability-selected active galactic nuclei in the Chandra Deep Field South
• A multi-wavelength survey of AGN in the XMM-LSS field: I. Quasar selection via the KX technique

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• Ensemble power spectral density of SDSS quasars in UV/optical bands
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• Dark Energy Survey Identification of A Low-Mass Active Galactic Nucleus at Redshift 0.823 from Optical Variability
• Long-term NIR Variability in the UKIDSS Ultra Deep Survey: a new probe of AGN activity at high redshift
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• Variability and transient search in the SUDARE-VOICE field: a new method to extract the light curves
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• X-ray Unveiling Events in a z~1.6 Active Galactic Nucleus in the 7 Ms Chandra Deep Field-South
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• On the Origin of the Strong Optical Variability of Emission-line Galaxies
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• VarIabiLity seLection of AstrophysIcal sources iN PTF (VILLAIN) I. Structure function fits to 71 million objects