The $N_H$ Distribution of Hard X-ray Selected AGN in the NEP Field

Abstract

X-ray surveys are one of the most unbiased methods for detecting Compton Thick (CT; $N_{\mathrm{H}}\ge 10^{24}$ cm${}^{-2}$) AGN, which are thought to comprise up to $60\%$ of AGN within $z\lesssim 1.0$. These CT AGN are often difficult to detect with current instruments, but the X-ray data within the JWST-North Ecliptic Pole (NEP) Time Domain Field (TDF) present a unique opportunity to study faint and obscured AGN. The NEP contains the deepest NuSTAR survey to date, and Zhao et al. (2024) detected 60 hard X-ray sources from the combined exposure of NuSTAR's Cycle 5 and 6 observations. In this work, we utilize the NuSTAR Cycle 5+6+8+9 data and simultaneous XMM-Newton observations in order to perform the first spectroscopic analysis of the 60-source catalog. We present this analysis and measure the $N_{\mathrm{H}}$ distribution of the sample. We measure an observed CT fraction of $0.13_{-0.04}^{+0.15}$ down to an observed $8-24$ keV flux of $6.0\times 10^{-14}$ erg/s/cm${}^2$, and we correct our analysis for absorption bias to estimate an underlying CT fraction of $0.32_{-0.08}^{+0.23}$. The derived obscuration distribution and CT fraction are consistent with population synthesis models and previous surveys.

24 pages, 14 figures, 7 tables

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