This study presents the capabilities of the AXIS telescope in estimating redshifts from X-ray spectra alone (X-ray redshifts, XZs). Through extensive simulations, we establish that AXIS observations enable reliable XZ estimates for more than 5500 obscured Active Galactic Nuclei (AGN) up to redshift z∼6 in the proposed deep (7 Ms) and intermediate (375 ks) surveys. Notably, at least 1600 of them are expected to be in the Compton-Thick regime (logNH/cm−2≥24), underscoring the pivotal role of AXIS in sample these elusive objects that continue to be poorly understood. XZs provide an efficient alternative for optical/infrared faint sources, overcoming the need for time-consuming spectroscopy, potential limitations of photometric redshifts, and potential issues related to multi-band counterpart association. This approach will significantly enhance the accuracy of constraints on the X-ray luminosity function and obscured AGN fractions up to high redshift. This White Paper is part of a series commissioned for the AXIS Probe Concept Mission; additional AXIS White Papers can be found at the AXIS website (http://axis.astro.umd.edu) with a mission overview here: arXiv:2311.00780.
@article{arxiv.2311.08449,
title = {X-ray Redshifts for Obscured Active Galactic Nuclei with AXIS Deep and Intermediate Surveys},
author = {Alessandro Peca and Nico Cappelluti and Stefano Marchesi and Edmund Hodges-Kluck and Adi Foord},
journal= {arXiv preprint arXiv:2311.08449},
year = {2024}
}