Studying the multi-phase interstellar medium in the Large Magellanic Cloud with SRG/eROSITA -- I. Analysis of diffuse X-ray emission

TL;DR

This study uses SRG/eROSITA X-ray data to analyze the distribution, properties, and composition of hot diffuse gas in the Large Magellanic Cloud, revealing its physical state, metallicity gradients, and interactions with cold gas.

Contribution

First comprehensive spatially resolved X-ray spectroscopic analysis of the LMC's hot ISM, integrating multiwavelength data to characterize its distribution, composition, and physical properties.

Findings

Measured total X-ray luminosity of hot ISM: 1.9×10^38 erg/s.

Constrained hot gas density (~5×10^-3 cm^-3) and temperature (~0.25 keV).

Identified metallicity gradients and regions with enhanced α-elements.

Abstract

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 multi-phase interstellar medium (ISM) of a galaxy across the electromagnetic spectrum. We aim 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. We construct multi-band 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 regions, we constrain the distribution, physical state, and composition of the hot ISM phase throughout the LMC. We combine our constraints with multiwavelength data to obtain a comprehensive view of the different ISM phases. We measure a total X-ray luminosity of the hot ISM phase of $1.9\times10^{38}\,\mathrm{erg\,s^{-1}}$ ($0.2-5.0\,\mathrm{keV}$ band), and constrain its thermal energy to around $5\times10^{54}\,\mathrm{erg}$. The typical density and temperature of the X-ray emitting plasma are around $5\times10^{-3}\,\mathrm{cm^{-3}}$ and $0.25\,\mathrm{keV}$, 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 HI 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 $\alpha$-enhancement, as expected from observed massive stellar populations there. In contrast, the enigmatic ``X-ray spur'' exhibits a local deficit in $\alpha$-elements, and a peak in hot-gas pressure at $P/k\sim10^5\,\mathrm{K\,cm^{-3}}$, consistent with a dominant energy input through tidally driven gas collisions.