The evolution of the X-ray luminosity functions of unabsorbed and absorbed AGNs out to z∼ 5

Abstract

We present new measurements of the evolution of the X-ray luminosity\nfunctions (XLFs) of unabsorbed and absorbed Active Galactic Nuclei (AGNs) out\nto z~5. We construct samples containing 2957 sources detected at hard (2-7 keV)\nX-ray energies and 4351 sources detected at soft (0.5-2 keV) energies from a\ncompilation of Chandra surveys supplemented by wide-area surveys from ASCA} and\nROSAT. We consider the hard and soft X-ray samples separately and find that the\nXLF based on either (initially neglecting absorption effects) is best described\nby a new flexible model parametrization where the break luminosity,\nnormalization and faint-end slope all evolve with redshift. We then incorporate\nabsorption effects, separately modelling the evolution of the XLFs of\nunabsorbed ($20<\\log N_\\mathrm{H}<22$) and absorbed ($22<\\log N_\\mathrm{H}<24$)\nAGNs, seeking a model that can reconcile both the hard- and soft-band samples.\nWe find that the absorbed AGN XLF has a lower break luminosity, a higher\nnormalization, and a steeper faint-end slope than the unabsorbed AGN XLF out to\nz~2. Hence, absorbed AGNs dominate at low luminosities, with the absorbed\nfraction falling rapidly as luminosity increases. Both XLFs undergo strong\nluminosity evolution which shifts the transition in the absorbed fraction to\nhigher luminosities at higher redshifts. The evolution in the shape of the\ntotal XLF is primarily driven by the changing mix of unabsorbed and absorbed\npopulations.\n