Probing the Hot Gaseous Halo of the Low-mass Disk Galaxy NGC 7793 with eROSITA and Chandra

Abstract

Galaxy formation models predict that local galaxies are surrounded by hot X-ray-emitting halos, which are technically difficult to detect due to their extended and low surface brightness nature. Previous X-ray studies have mostly focused on disk galaxies more massive than the Milky Way, with essentially no consensus on the halo X-ray properties at the lower mass end. We utilize the early-released eROSITA and archival Chandra observations to analyze the diffuse X-ray emission of NGC 7793, a nearby spiral galaxy with an estimated stellar mass of only 3.2 × 109M⊙. We find evidence for extraplanar hot gas emission from both the radial and vertical soft X-ray intensity profiles, which spreads up to a galactocentric distance of ∼6 kpc, nearly 30% more extended than its stellar disk. Analysis of the eROSITA spectra indicates that the hot gas can be characterized by a temperature of keV, with 0.5–2 keV unabsorbed luminosity of 1.3 × 1038 erg s−1. We compare our results with the IllustrisTNG simulations and find overall consistence on the disk scale, whereas excessive emission at large radii is predicted by TNG50. This work provides the latest detection of hot corona around a low-mass galaxy, putting new constraints on state-of-the-art cosmological simulations. We also verify the detectability of hot circumgalactic medium around even low-mass spirals with future high-resolution X-ray spectrometers such as the Hot Universe Baryon Surveyor.