DISCOVERY OF NUCLEAR X-RAY SOURCES IN SINGS GALAXIES

Abstract

We present the results of a search for nuclear X-ray activity in nearby galaxies using Chandra archival data in a sample of 62 galaxies from the Spitzer Infrared Nearby Galaxy Survey. We detect 37 nuclear X-ray sources; seven of these are new detections. Most of the nuclear X-ray sources are likely to be active galactic nuclei (AGNs). The fraction of galaxies hosting AGNs is thus about 60%, much higher than that found with optical searches, and demonstrates the efficacy of X-ray observations to find hidden AGNs in optically normal galaxies. We find that the nuclear X-ray sources are preferentially present in earlier type galaxies. Unlike what is observed at high redshift for high-luminosity AGNs, we do not find a strong correlation between the AGN luminosity and the 24 mu m luminosity of the host galaxy; we find a strong correlation with the 3.6 mu m luminosity instead. This suggests that at the present epoch, the accretion rate depends on the total mass of the galaxy, as perhaps does the black hole mass.