PI: Ioannis Georgantopoulos, National Athens Observatory, email@example.com
Address: Institute of Astronomy & Astrophysics, V. Paulou \& I. Metaxa, Athens 15236, Greece
CoI: Antonis Georgakakis, Imperial College, London, UK
CoI: Dimitris Athanasiadis, National Observatory Athens, Greece
CoI: Spyros Kitsionas, Astrophysikalisches Institut Potsdam
Title: Selecting AGN in the hardest possible X-ray band
Abstract: The \it intrinsic N_H distribution of AGN, a key parameter for understanding the diffuse X-ray background, remains poorly constrained because of our inability to compile unbiased AGN samples. X-ray surveys, although a powerful tool for studying AGN, are not completely unbiased, selecting against obscured systems, depending on the energy band used. Here we propose to improve on the number of redshifts known from existing surveys by following at optical wavelengths a unique AGN sample selected at the hardest band currently accessible to X-ray imaging: 7.5-12 keV. Selection at these ultra-hard energies extends by about 1 dex, compared to previous efforts, the column density baseline directly accessible to observations. This is a major step toward constraining the true underlying N_H distribution of AGN and refining current models.
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