Extra! Extra! X-ray Emission!: X-rays in Romulus25, Part II - Physical Drivers of X-ray Emission in the CGM
Abstract
Characterizing the hot (T ~ 106 K) circumgalactic medium (CGM) around Milky Way-mass (MW-mass) galaxies is critical to a full understanding of galaxy evolution. In this second paper of the "X-rays in Romulus25" series, we unpack the specific physical processes giving rise to the presence of hot X-ray emitting gas in the halos of galaxies from the Romulus25 (R25) simulation, focusing on L* galaxies. We determine that a strong correlation appears between the mass of hot CGM gas, Mgas, T > 105.5 K, and the X-ray emissivity, εχ, measured in the first paper of this series, (Sanchez et al. 2026a, submitted). There is also a secondary correlation between Mgas, T > 105.5 K and εχ with the average metallicity of the hot CGM gas, Z̅gas, T > 105.5 K. We use the well-studied PIONEER simulations from Sanchez et al. (2019), a set of zoom-in MW-mass galaxies run with the genetic modification technique of Roth et al. (2016) and the same physics as R25, to interpret these correlations. We determine that the presence of hot X-ray emitting gas is determined by two key processes: 1) the quantity of hot gas mass in the CGM, Mgas, T > 105.5 K, is set by the combined total energy injection of both stellar and AGN feedback, and 2) together the average temperature and metallicity of the hot CGM changes the soft X-ray spectrum of the gas resulting in brighter metal-rich CGM and dimmer metal-poor CGM for the same quantity of Mgas, T > 105.5 K. These results indicate, for the first time, that metal-rich gas halos may bias X-ray observations of MW-mass galaxies.
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BibTeX
@misc{sanchez2026extra,
title = {{Extra! Extra! X-ray Emission!: X-rays in Romulus25, Part II - Physical Drivers of X-ray Emission in the CGM}},
author = {N. Nicole Sanchez and Andrew Benson and Gwen Rudie and Ben Oppenheimer and Hannah Bish and John ZuHone and Michael Tremmel},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.37769},
eprint = {2610.37769},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.37769},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Extra! Extra! X-ray Emission!: X-rays in Romulus25, Part II - Physical Drivers of X-ray Emission in the CGM
AU - N. Nicole Sanchez
AU - Andrew Benson
AU - Gwen Rudie
AU - Ben Oppenheimer
AU - Hannah Bish
AU - John ZuHone
AU - Michael Tremmel
PY - 2026
DA - 2026/10/27
PB - arXiv
DO - 10.48550/arxiv.2610.37769
UR - https://arxiv.org/abs/2610.37769
AB - Characterizing the hot (T ~ 10^6 K) circumgalactic medium (CGM) around Milky Way-mass (MW-mass) galaxies is critical to a full understanding of galaxy evolution. In this second paper of the "X-rays in Romulus25" series, we unpack the specific physical processes giving rise to the presence of hot X-ray emitting gas in the halos of galaxies from the Romulus25 (R25) simulation, focusing on L_* galaxies. We determine that a strong correlation appears between the mass of hot CGM gas, M_gas, T > 10^5.5 K, and the X-ray emissivity, ε_χ, measured in the first paper of this series, (Sanchez et al. 2026a, submitted). There is also a secondary correlation between M_gas, T > 10^5.5 K and ε_χ with the average metallicity of the hot CGM gas, Z̅_gas, T > 10^5.5 K. We use the well-studied PIONEER simulations from Sanchez et al. (2019), a set of zoom-in MW-mass galaxies run with the genetic modification technique of Roth et al. (2016) and the same physics as R25, to interpret these correlations. We determine that the presence of hot X-ray emitting gas is determined by two key processes: 1) the quantity of hot gas mass in the CGM, M_gas, T > 10^5.5 K, is set by the combined total energy injection of both stellar and AGN feedback, and 2) together the average temperature and metallicity of the hot CGM changes the soft X-ray spectrum of the gas resulting in brighter metal-rich CGM and dimmer metal-poor CGM for the same quantity of M_gas, T > 10^5.5 K. These results indicate, for the first time, that metal-rich gas halos may bias X-ray observations of MW-mass galaxies.
ER -