A XRISM study of highly ionized iron emission lines from the low-Eddington-ratio AGN in NGC 7213

We present an analysis of XRISM and NuSTAR data obtained for the nearby low-Eddington active galactic nucleus NGC 7213. Our goal is to examine whether its He-like and H-like iron emission lines can be reproduced by photoionization or collisional ionization processes. Using the broad-band energy coverage of our data (2–60 keV), we first constrained the continuum shape. Then, we focused on the iron-K band in the Resolve spectrum. Gaussian fits to Fe xxv He(Formula presented) and Fe xxvi Ly(Formula presented) lines suggest that they may have different velocity widths: (Formula presented)  km s(Formula presented) for Fe xxv and (Formula presented)  km s(Formula presented) for Fe xxvi. In this case, the He(Formula presented) resonance line (w) and forbidden line (z) have similar intensities of (Formula presented) –(Formula presented)  ph s(Formula presented)  cm(Formula presented), while the intercombination lines (x + y) are not significantly detected with upper limits of (Formula presented)  ph s(Formula presented)  cm(Formula presented). Motivated by the possible difference in the line widths, we tested one- and two-zone photoionized and collisionally ionized models. Our results show that the additional ionized component is not significantly required, and the current data cannot uniquely determine whether photoionization or collisional ionization dominates. Moreover, if the Fe xxv He(Formula presented) complex implies that the weak x + y lines are suppressed relative to the w and z lines, such a structure is difficult to reproduce with either ionization model adopted. Finally, by comparing NGC 7213 with M 81(Formula presented), accreting at a much lower Eddington ratio of (Formula presented), we found a decrease in the density of the gas responsible for highly ionized iron emission, which may imply that the density decreases with decreasing (Formula presented) .