Peca, AlessandroCappelluti, NicoMarchesi, StefanoHodges-Kluck, EdmundFoord, Adi2024-07-262024-07-262024-06-01Peca, Alessandro, Nico Cappelluti, Stefano Marchesi, Edmund Hodges-Kluck, and Adi Foord. “X-Ray Redshifts for Obscured Active Galactic Nuclei with AXIS Deep and Intermediate Surveys.” Universe 10, no. 6 (June 2024): 245. https://doi.org/10.3390/universe10060245.https://doi.org/10.3390/universe10060245http://hdl.handle.net/11603/35109This 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 (AGNs) 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 (log Nₕ/cm⁻²≥24), underscoring the pivotal role of AXIS in sampling 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, the 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 redshifts. 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.8 pagesen-USThis work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.Public Domainhttps://creativecommons.org/publicdomain/mark/1.0/active galactic nucleiprobesredshiftssurveysX-raysText