Variability-Selected AGNs in the VST-SUDARE Survey of the COSMOS Field

Variability is characteristic of active galaxies; luminosity variations generally occur at all wavelengths, affecting both continuum and line emission, with timescales and amplitudes depending on the wavelength. We made use of optical variability to select AGNs in the VST-SUDARE survey of the COSMOS field, and confirmed 95 % of them by means of multiwavelength data from overlapping surveys. The analysis returns a sample of AGN candidates with 81 % purity and 15 % completeness with respect to the X-ray confirmed AGNs in the field with an optical counterpart. This study provides an estimate of the reliability of the AGN selection techniques based on variability, which will be used by future wide-field surveys, such as those by LSST.