Seyfert galaxies and the hard X-ray background: Artificial Chandra observations of z=0.3 active galaxies

Deep X-ray surveys have resolved much of the X-ray background radiation below 2 keV into discrete sources, but the background above 8 keVremains largely unresolved. The obscured ( type 2) active galactic nuclei (AGNs) that are expected to dominate the hard X-ray background have not yet been detected in sufficient numbers to account for the observed background flux. However, deep X-ray surveys have revealed large numbers of faint quiescent and star-burst galaxies at moderate redshifts. In hopes of recovering the missing AGN population, it has been suggested that the defining optical spectral features of low-luminosity Seyfert nuclei at large distances may be overwhelmed by their host galaxies, causing them to appear optically quiescent in deep surveys. We test this possibility by artificially red-shifting a sample of 23 nearby, well-studied active galaxies to z = 0.3, testing them for X-ray AGN signatures, and comparing them to the objects detected in deep X-ray surveys. We find that these redshifted galaxies have properties consistent with the deep-field normal and optically bright, X-ray-faint galaxy (OBXF) populations, supporting the hypothesis that the numbers of AGNs in deep X-ray surveys are being underestimated and suggesting that OBXFs should not be ruled out as candidate AGN hosts that could contribute to the hard X-ray background source population.