Dissecting the Nuclear Structure of NGC 5548 with XRISM I. Physical Properties of the Highly Ionized Outflows

We present a detailed spectral analysis of an X-Ray Imaging and Spectroscopy Mission (XRISM) observation of the prototypical Seyfert 1 galaxy NGC 5548. XRISM’s Resolve microcalorimeter reveals, for the first time, highly ionized outflows in this active galactic nucleus (AGN) through the detection of Fe xxv and Fe xxvi absorption lines in the Fe K band. Modeling the XRISM/Resolve spectrum alongside XMM-Newton Reflection Grating Spectrometer data allows us to probe the ionization and kinematic structure of the outflows in this AGN. We identify four distinct ionization components, with ionization parameters (Formula presented) logξ ranging from 0.9 to 3.4. Three of these components are further resolved into two velocity subcomponents, demonstrating the multiphase structure of the outflows. The measured outflow velocities span 240–2730 km s−1. We find a trend of increasing column density with ionization parameter (ξ), along with a general pattern of increasing outflow velocity with ξ. The XRISM/Resolve spectrum provides a far more detailed absorption measure distribution than was previously possible, revealing two distinct slopes above and below (Formula presented) logξ∼2.6. A comparison of the Fe xxv absorption line profile with UV absorption lines (C iv and Lyα) observed with the Hubble Space Telescope reveals both overlaps and deviations. The XRISM/Resolve results suggest a multiphase, clumpy outflow in NGC 5548, consistent with a “hybrid wind” scenario in which the observed parameter trends arise from multiple origins and driving mechanisms.