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arXiv · 2504.03840

Retrieving the hot circumgalactic medium physics from the X-ray radial profile from eROSITA with an IlustrisTNG-based forward model

Soumya Shreeram·Johan Comparat·Andrea Merloni·Gabriele Ponti·Paola Popesso·Yi Zhang·Kirpal Nandra·Mara Salvato·Ilaria Marini·Johannes Buchner·Nicola Locatelli·Zsofi Igo
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Abstract

Recent eROSITA measurements of the radial profiles of the hot CGM in the Milky-Way stellar mass (MW-mass) regime provide us with a new benchmark to constrain the hot gas around MW-mass central and satellite galaxies and their halo mass distributions. Modelling this rich data set with state-of-the-art hydrodynamical simulations is required to further our understanding of the shortcomings in the current paradigm of galaxy formation and evolution models. We develop forward models for the stacked X-ray radial surface brightness profile measured by eROSITA around MW-mass galaxies. Our model contains two emitting components: hot gas (around central galaxies and satellite galaxies hosted by more massive halos) and X-ray point sources (X-ray binaries and Active Galactic Nuclei). We model the hot gas profile using the TNG300-based products. We generate mock observations with our TNG300-based model (matching stellar mass and redshift with observations) with different underlying halo mass distributions. We show that for the same mean stellar mass, a factor 2x increase in the mean value of the underlying halo mass distribution results in a ~4x increase in the stacked X-ray luminosity from the hot CGM. The point sources are described by a simple point-spread-function (PSF) of eROSITA, and we fit their normalization in this work. Using empirical models to derive a permissible range of AGN and XRB luminosities in the MW-mass X-ray galaxy stack, we choose our forward model best describing the hot CGM for the eROSITA observations. We find that at < 40 kpc from the galaxy centre, the hot CGM from central galaxies and the X-ray point sources emission each account for 40-50% of the total X-ray emission budget. In summary, we show that the gas physics driving the shape of the observed hot CGM (in stellar-mass-selected samples) is tightly correlated by the underlying halo-mass distribution (abridged).

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Soumya Shreeram, Johan Comparat, Andrea Merloni, Gabriele Ponti, Paola Popesso, Yi Zhang, Kirpal Nandra, Mara Salvato, Ilaria Marini, Johannes Buchner, Nicola Locatelli, Zsofi Igo. 2025-04-04. Retrieving the hot circumgalactic medium physics from the X-ray radial profile from eROSITA with an IlustrisTNG-based forward model. https://doi.org/10.1051/0004-6361%2F202554508

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