AGN Populations in Large Volume X-ray Surveys: Photometric Redshifts and Population Types found in the Stripe 82X Survey

TL;DR

This study presents a comprehensive catalog of X-ray sources in the Stripe 82X survey, with photometric redshifts for most sources, aiding the understanding of AGN populations in large-area surveys.

Contribution

The paper provides an updated multi-wavelength catalog with photometric redshifts for nearly all X-ray sources in Stripe 82X, addressing challenges of wide-area AGN identification.

Findings

Photometric redshifts for 96% of sources with $\sigma_{nmad}=0.06$

Outlier fraction of 13.7% in redshift estimates

Guidance for future large-area surveys like eROSITA and LSST

Abstract

Multi-wavelength surveys covering large sky volumes are necessary to obtain an accurate census of rare objects such as high luminosity and/or high redshift active galactic nuclei (AGN). Stripe 82X is a 31.3 deg$^2$ X-ray survey with $Chandra$ and $XMM$-Newton observations overlapping the legacy Sloan Digital Sky Survey (SDSS) Stripe 82 field, which has a rich investment of multi-wavelength coverage from the ultraviolet to the radio. The wide-area nature of this survey presents new challenges for photometric redshifts for AGN compared to previous work on narrow-deep fields because it probes different populations of objects that need to be identified and represented in the library of templates. Here we present an updated X-ray plus multi-wavelength matched catalog, including $Spitzer$ counterparts, and estimated photometric redshifts for 5961 (96% of a total of 6181) X-ray sources, which have a normalized median absolute deviation, $\sigma_{\rm nmad}$ = 0.06 and an outlier fraction, $\eta$ = 13.7%. The populations found in this survey, and the template libraries used for photometric redshifts, provide important guiding principles for upcoming large-area surveys such as $eROSITA$ and 3$XMM$ (in X-ray) and the Large Synoptic Survey Telescope (LSST; optical).