The halo mass dependence of physical and observable properties in the circumgalactic medium at z = 0

Cook, AWS ORCID: 0009-0001-9328-6903, Van de Voort, F ORCID: 0000-0002-6301-638X, Pakmor, R ORCID: 0000-0003-3308-2420 and Grand, RJJ ORCID: 0000-0001-9667-1340 (2025) The halo mass dependence of physical and observable properties in the circumgalactic medium at z = 0. Monthly Notices of the Royal Astronomical Society, 543 (2). pp. 1224-1238. ISSN 0035-8711

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Abstract

We study the dependence of the physical and observable properties of the circumgalactic medium on its halo mass in 25 highresolution cosmological ‘zoom-in’ simulations from the Auriga suite. We focus on the current epoch (z = 0) and on halo masses
of 1010 M ≤ M200c ≤ 1012 M and stellar masses of 107 M ≤ M ≤ 1011 M. The mass resolution of our simulations
is 5.4 × 103 M. This work analyses the temperature, density, metallicity, and radial velocity of these haloes and the column
density of H I, Mg II, Si II, C IV, and O VI. We find median temperature and metallicity increase with halo mass as expected. We find
a larger scatter in temperature at higher halo masses, suggesting that the multiphase nature of the CGM is halo-mass-dependent.
Our H I column densities show good agreement with observations at all radii. Mg II and Si II match observations between 0.1R200c
and 0.3R200c, but decrease steeply with radius. O VI column densities are underpredicted by our simulations for stellar masses in
the range 109.5 M ≤ M < 1010.2 M at large radii with reasonable agreement at 1011 M. C IV column densities agree with
observational detections above a halo mass of 109.5 M. We find that O VI (H I) traces the highest (lowest) temperatures, and
the lowest (highest) density and metallicity. O VI (C IV) is photoionized (collisionally ionized) at low (high) halo masses with
a transition to higher temperatures at 1011 M. Our results demonstrate similarities and discrepancies between simulations of
Milky Way-mass haloes and observations. They also show further observational constraints are needed in less massive haloes.
Key words: MHD – methods: numerical – galaxies: dwarf – galaxies: evolution – galaxies: haloes – cosmology: theory.

Item Type:	Article
Uncontrolled Keywords:	5101 Astronomical Sciences; 51 Physical Sciences; 0201 Astronomical and Space Sciences; Astronomy & Astrophysics; 5101 Astronomical sciences; 5107 Particle and high energy physics; 5109 Space sciences
Subjects:	Q Science > QB Astronomy Q Science > QC Physics
Divisions:	Astrophysics Research Institute
Publisher:	Oxford University Press (OUP)
Date of acceptance:	9 September 2025
Date of first compliant Open Access:	6 January 2026
Date Deposited:	06 Jan 2026 14:59
Last Modified:	06 Jan 2026 14:59
DOI or ID number:	10.1093/mnras/staf1537
URI:	https://researchonline.ljmu.ac.uk/id/eprint/27821

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