Identification and Characterization of a Large Sample of Distant Active Dwarf Galaxies in XMM-SERVS

Active dwarf galaxies are important because they contribute to the evolution of dwarf galaxies and can reveal their hosted massive black holes. However, the sample size of such sources is still highly limited, especially beyond the local universe. In this work, we search for active dwarf galaxies in the recently completed XMM-SERVS survey, which is currently the largest medium-depth X-ray survey. After considering several factors that may lead to misidentifications, we identify 87 active dwarf galaxies at z < 1.2, which constitutes the current largest sample beyond the local universe. Our sources are generally less obscured than the prediction based on the massive-AGN (active galactic nucleus) X-ray luminosity function. Their Eddington ratios and X-ray bolometric corrections also significantly deviate from the expected relation. We find that our sources reside in similar environments as for inactive dwarf galaxies. We further quantify the accretion distribution of the dwarf-galaxy population after considering various selection effects and then analyze the dependence of the active fraction on stellar mass, redshift, and luminosity. Throughout this work, we highlight several fundamental problems in reliably measuring some basic parameters for distant active dwarf galaxies.