XRISM Reveals a Remnant Torus in the Low-luminosity AGN M81*

Up to 40% of galaxies in the local Universe host a low-luminosity active galactic nucleus (LLAGN), making it vital to understand this mode of black hole accretion. However, the presence or absence of Seyfert-like geometries—an accretion disk close to the black hole, an optical broad-line region, and a molecular torus—remains uncertain owing to the low flux levels of sources within this class. Herein we present an analysis of an XRISM/Resolve spectrum of M81*, the LLAGN in the heart of the nearby spiral galaxy M81. A weak, neutral Fe K emission line is detected and resolved into Kα,1 and Kα,2 components. It shows a negligible velocity shift and weak broadening (FWHM ) that corresponds to an inner emission radius of r ≥ 2.7 × 104 GM c−2 for likely inclinations. The Fe Kα line likely traces a torus. The upper limit on additional splitting of the Fe Kα line components translates to a limit on the local magnetic field of B ≤ 3.5 × 108 G, assuming Zeeman splitting. The spectra also reveal ionized plasma(s) through He-like Fe xxv and H-like Fe xxvi emission lines. These can be fit equally well assuming photoionization and collisional excitation. The H-like Fe xxvi line is better described when a second component is included with a redshift of v = 1600 km s−1, but this addition is of marginal statistical significance. We discuss these results in the context of radiatively inefficient accretion flow models, magnetically arrested disks, and possible links to the Fermi bubbles in the Milky Way.