A Detection of an X-ray Wind and an Ionized Disk in the Chandra HETGS Observation of the Seyfert 2 Galaxy IRAS 18325-5926

TL;DR

This paper analyzes Chandra HETGS data of Seyfert 2 galaxy IRAS 18325-5926, revealing ionized winds, a broad Fe K emission line, and insights into the geometry of the accretion disk and surrounding gas.

Contribution

It presents the first detection of a blueshifted ionized absorber and characterizes the accretion disk and outflows in IRAS 18325-5926 using high-resolution X-ray spectroscopy.

Findings

Detection of a blueshifted ionized absorber with specific velocity and ionization parameters.

Identification of a broad Fe K emission line likely from a highly ionized accretion disk.

Evidence suggesting a patchy surrounding gas or a grazing viewing angle of the obscuring torus.

Abstract

We analyze the \textit{Chandra} High Energy Transmission Grating Spectrometer (HETGS) observation of the Seyfert $2$ AGN IRAS\,18325-5926. We detect a $v=-360^{+41}_{-66}$~km~s$^{-1}$ blueshifted ionized absorber in the X-ray spectrum, with photoionization parameter $\log\xi=2.0^{+0.1}_{-0.1}$ and hydrogen column density $N_{\rm H}=1.55^{+0.75}_{-0.38}\times10^{21}$~cm$^{-2}$. The absorber may be a photoionized wind originating in the obscuring torus/global covering around the black hole or outer edge of the accretion disk. The estimated mass outflow rate suggests that the supermassive black hole in IRAS\,18325-5926 may significantly affect the large-scale environment of the host galaxy, unless the solid angle subtended by the outflow or the gas filling factor is small. A second warm absorber may be needed to explain the absorption features in the vicinity of the iron K edge, although insufficient counts in the data beyond $7.0$~keV make it difficult to assess the nature of the second absorber. Most plausible is a high ionization ($\log\xi\sim 2.3$ to $2.6$), high column density ($N_{\rm H}\sim10^{23}$~cm$^{-2}$) absorber with $v\sim -3000$ to $0$~km~s$^{-1}$, although these parameters are not well constrained. We also examine the broad Fe K emission line in the spectrum, which is likely due to Fe XXV in a highly ionized accretion disk inclined at $25^\circ$, consistent with the \textit{XMM-Newton} EPIC observations of the emission line. Because we are able to view both the obscuring gas and the accretion disk of IRAS\,18325-5926, the surrounding gas of IRAS\,18325-5926 may be patchy or we are viewing the system at an angle just grazing the obscuring torus.