Variability selected AGNs in the Chandra Deep Field South

Variability is a fundamental property of active galactic nuclei (AGN) and is adopted here as a selection criterion using multi epoch surveys. Low Luminosity AGNs (LLAGNs) are contaminated by the light of the host galaxies, thus they cannot be detected by the color techniques. Their evolution in cosmic time is poorly known and consistency with the evolution derived from X-ray detected samples has not been established. Since several variability surveys are conducted for the detection of supernovae (SNe), we have re-analyzed the SN datasets with a variability criterion optimized for AGN detection in order to select a new AGN sample and study its properties. We have used images taken in the framework of the STRESS supernova survey. We selected the AXAF field centered in the Chandra Deep Field South where, besides the deep Xray survey also various optical catalogs exist. Our method has yielded 132 variable AGN candidates and most of them are X-ray sources. A spectroscopic campaign for part of our candidates confirms their AGN nature. Most of the results have been published in Trevese et al. 2008.