Title:	Misty, patchy, and turbulent: constraining the cool circumgalactic medium with mCC
Authors:	Bisht, Mukesh Singh Sharma, Prateek Dutta, Alankar Nath, Biman B.
Keywords:	Galaxy halo – galaxies haloes – quasars absorption lines
Issue Date:	12-Aug-2025
Publisher:	Oxford University Press on behalf of Royal Astronomical Society
Citation:	Monthly Notices of the Royal Astrnomical Society, 2025, Vol. 542, p1573
Abstract:	The circumgalactic medium (CGM) is the largest baryon reservoir around galaxies, but its extent, mass, and temperature distribution remain uncertain. We propose that cool gas (∼ 104 K) in the CGM resides in clumpy structures referred to as cloud complexes (CCs) rather than uniformly filling the entire CGM volume. Each CC contains a mist of tiny cool cloudlets dispersed in a warm/hot medium (∼ 105 –106 K). Modelling CCs in the mist limit (unit area covering fraction within a CC) simplifies the calculation of observables like ion absorption columns, equivalent widths, compared to modelling individual cloudlets from first principles. Through Monte Carlo realizations of CCs, we explore how CC properties affect the observed variation in observables. We find that a power-law distribution of CCs (dNCC /dR ∝ R−1 ) with a total of ∼ 103 CCs each with a radius of ∼ 10 kpc and total cool gas mass of ∼ 1010 M reproduces Mg II column density and equivalent width distribution trends with impact parameter for the COS-Halos sample (Werk+ 2013). We further show that the area-averaged Mg II column density, combined with the area covering fraction, provides a robust proxy for estimating the cool CGM mass, independent of other model parameters. Modelling a larger number of (smaller size) cloudlets within a CC shows that line blending from individual cloudlets results in turbulent broadening on the CC scale. This work presents a practical framework for linking CGM models with observations of a multiphase CGM, providing insights into the distribution of cool gas in galaxy haloes.
Description:	Open Access
URI:	http://hdl.handle.net/2289/8523
Alternative Location:	https://doi.org/10.1093/mnras/staf1319
Copyright:	2025 The Author(s)
Appears in Collections:	Research Papers (A&A)

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