Unveiling the Hot Interstellar Medium in Nearby Galaxies with eROSITA

Diffuse X-ray emission in galaxies originates from stellar-feedback-heated gas and unresolved compact sources. We investigate its thermal component and the scaling of X-ray luminosity with star formation rate (SFR), including galaxies with very low SFRs. We analyzed eROSITA/SRG data from the four all-sky surveys (eRASS:4) for a blind, volume-limited sample of 140 galaxies within 25 Mpc from the Updated Nearby Galaxy Catalog (Karachentsev et al. 2013), cross-matched with HECATEv2 (Kyritsis et al. 2026b). Early-type galaxies were analyzed separately, while star-forming galaxies were divided into low-, medium-, and high-specific-SFR (sSFR) subsamples. We modeled the integrated X-ray spectra with thermal plasma and power-law components, stacked spectra for each subsample, and derived total and thermal X-ray luminosities. The stacked spectra show a stronger soft thermal component at high sSFR, whereas low-sSFR and early-type galaxies are increasingly dominated by the harder non-thermal continuum. For star-forming galaxies, the total 0.5-8 keV luminosity follows L X about 39.5 + 0.9 SFR, with an intrinsic scatter of about 0.9 dex. The 0.5-2 keV thermal luminosity follows L X about 38.7 + 1.1 SFR, with an intrinsic scatter of about 0.7 dex. The thermal luminosity remains well correlated with SFR down to about 10-5, M, yr-1 and is consistent with previous relations for star-forming galaxies. By contrast, the flatter and more scattered total X-ray luminosity-SFR relation suggests that unresolved X-ray binaries likely dominate at low SFR, while thermal X-ray emission remains a robust tracer of stellar feedback.