Unveiling the Hot Interstellar Medium in Nearby Galaxies with eROSITA
Abstract
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 log LX ∼ 39.5 + 0.9logSFR, with an intrinsic scatter of about 0.9 dex. The 0.5-2 keV thermal luminosity follows log LX ∼ 38.7 + 1.1logSFR, with an intrinsic scatter of about 0.7 dex. The thermal luminosity remains well correlated with SFR down to ∼ 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.
Related
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BibTeX
@misc{laktionov2026unveiling,
title = {{Unveiling the Hot Interstellar Medium in Nearby Galaxies with eROSITA}},
author = {Roman Laktionov and Manami Sasaki and Elias Kyritsis and Andreas Zezas and Steven Hämmerich and Fiona Knies and Jörn Wilms and Frank Haberl and Martin G. H. Krause and Ashley Coombs and Philipp Weber and Aafia Zainab},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.16936},
eprint = {2610.16936},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.16936},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Unveiling the Hot Interstellar Medium in Nearby Galaxies with eROSITA
AU - Roman Laktionov
AU - Manami Sasaki
AU - Elias Kyritsis
AU - Andreas Zezas
AU - Steven Hämmerich
AU - Fiona Knies
AU - Jörn Wilms
AU - Frank Haberl
AU - Martin G. H. Krause
AU - Ashley Coombs
AU - Philipp Weber
AU - Aafia Zainab
PY - 2026
DA - 2026/10/12
PB - arXiv
DO - 10.48550/arxiv.2610.16936
UR - https://arxiv.org/abs/2610.16936
AB - 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 log L_X ∼ 39.5 + 0.9logSFR, with an intrinsic scatter of about 0.9 dex. The 0.5-2 keV thermal luminosity follows log L_X ∼ 38.7 + 1.1logSFR, with an intrinsic scatter of about 0.7 dex. The thermal luminosity remains well correlated with SFR down to ∼ 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.
ER -