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 × 10 9 M ⊙ . 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>0.1</mml:mn> <mml:msubsup> <mml:mrow> <mml:mn>8</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.03</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.02</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> keV, with 0.5–2 keV unabsorbed luminosity of 1.3 × 10 38 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.