Studying the multiphase interstellar medium in the Large Magellanic Cloud with SRG/eROSITA

I. Analysis of diffuse X-ray emission

¹ Dr. Karl Remeis Observatory, Erlangen Centre for Astroparticle Physics, Friedrich-Alexander-Universität Erlangen-Nürnberg, Sternwartstrasse 7, 96049 Bamberg, Germany
² Max-Planck Institut für extraterrestrische Physik, Giessenbachstrasse, 85748 Garching, Germany
³ Institute for Advanced Study, Gifu University, 1-1 Yanagido, Gifu, Gifu 501-1193, Japan
⁴ Department of Physics, Graduate School of Science, Nagoya University, Furo-cho, Chikusa, Nagoya 464-8602, Japan
⁵ Western Sydney University, Locked Bag 1797, Penrith South DC, NSW 2751, Australia
⁶ International Centre for Radio Astronomy Research (ICRAR), University of Western Australia, 35 Stirling Highway, Perth, WA 6009, Australia
⁷ Australia Telescope National Facility, CSIRO, Space and Astronomy, PO Box 76, Epping, NSW 1710, Australia
⁸ Cerro Tololo Inter-American Observatory, NOIRLab, Casilla 603, La Serena, Chile
⁹ Department of Physics, Maynooth University, Maynooth, Co. Kildare, Ireland

^★ Corresponding author: mgf.mayer@fau.de

Received: 1 April 2025
Accepted: 27 June 2025

Abstract

Context. The Large Magellanic Cloud (LMC), being a nearby and actively star-forming satellite galaxy of the Milky Way, is an ideal site to observe the multiphase interstellar medium (ISM) of a galaxy across the electromagnetic spectrum.

Aims. We aimed to exploit the available SRG/eROSITA all-sky survey data to study the distribution, composition and properties of the diffuse X-ray emitting hot gas in the LMC.

Methods. We constructed multiband X-ray images of the LMC, reflecting the morphology and temperatures of the diffuse hot gas. By performing spatially resolved X-ray spectroscopy of 175 independent regions, we constrained the distribution, temperature, mass, energetics and composition of the hot ISM phase throughout the galaxy, while also testing for the presence of X-ray synchrotron emission. We combined our constraints with multiwavelength data to obtain a comprehensive view of the different ISM phases.

Results. We measure a total X-ray luminosity of the hot ISM phase of 1.9 × 10³⁸ erg s⁻¹ (0.2–5.0 keV band), and constrain its thermal energy to around 9 × 10⁵⁴ erg. The typical density and temperature of the X-ray emitting plasma are around 5 × 10⁻³ cm⁻³ and 0.25 keV, respectively, with both exhibiting broad peaks in the southeast of the LMC. The observed degree of X-ray absorption correlates strongly with the distribution of foreground H I gas, whereas a spatial anticorrelation between the hot and cold ISM phases is visible on sub-kpc scales within the disk. The abundances of light metals show a strong gradient throughout the LMC, with the north and east exhibiting a strong α-enhancement, as expected from observed massive stellar populations there. In contrast, the enigmatic “X-ray spur” exhibits a local deficit in α-elements, and a peak in hot-gas pressure at P/k ∼ 10⁵ K cm⁻³, consistent with a dominant energy input through tidally driven gas collisions. Finally, we tentatively identify spectroscopic signatures of nonthermal X-ray emission from the supergiant shell LMC 2, although contamination by straylight cannot be excluded.