A new extensive catalog of optically variable AGN in the GOODS Fields and a new statistical approach to variability selection

TL;DR: In this paper, the authors discuss and test different statistical methods for the detection of variability in sparsely sampled data that allow full control over the false positive rates and present a catalog of variable sources in the z band in both the North and South fields.

Abstract: Variability is a property shared by practically all AGN This makes variability selection a possible technique for identifying AGN Given that variability selection makes no prior assumption about spectral properties, it is a powerful technique for detecting both low-luminosity AGN in which the host galaxy emission is dominating and AGN with unusual spectral properties In this paper, we will discuss and test different statistical methods for the detection of variability in sparsely sampled data that allow full control over the false positive rates We will apply these methods to the GOODS North and South fields and present a catalog of variable sources in the z band in both GOODS fields Out of 11931 objects checked, we find 155 variable sources at a significance level of 999%, corresponding to about 13% of all objects After rejection of stars and supernovae, 139 variability selected AGN remain Their magnitudes reach down as faint as 255 mag in z Spectroscopic redshifts are available for 22 of the variability selected AGN, ranging from 0046 to 37 The absolute magnitudes in the rest-frame z-band range from ~ -18 to -24, reaching substantially fainter than the typical luminosities probed by traditional X-ray and spectroscopic AGN selection in these fields Therefore, this is a powerful technique for future exploration of the evolution of the faint end of the AGN luminosity function up to high redshifts