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Published August 20, 2022 | Submitted + Published
Journal Article Open

The Impact of Cosmic Rays on the Kinematics of the Circumgalactic Medium

Abstract

We use hydrodynamical simulations of two Milky Way–mass galaxies to demonstrate the impact of cosmic-ray pressure on the kinematics of cool and warm circumgalactic gas. Consistent with previous studies, we find that cosmic-ray pressure can dominate over thermal pressure in the inner 50 kpc of the circumgalactic medium (CGM), creating an overall cooler CGM than that of similar galaxy simulations run without cosmic rays. We generate synthetic sight lines of the simulated galaxies' CGM and use Voigt profile-fitting methods to extract ion column densities, Doppler-b parameters, and velocity centroids of individual absorbers. We directly compare these synthetic spectral line fits with HST/COS CGM absorption-line data analyses, which tend to show that metallic species with a wide range of ionization potential energies are often kinematically aligned. Compared to the Milky Way simulation run without cosmic rays, the presence of cosmic-ray pressure in the inner CGM creates narrower O vi absorption features and broader Si iii absorption features, a quality that is more consistent with observational data. Additionally, because the cool gas is buoyant due to nonthermal cosmic-ray pressure support, the velocity centroids of both cool and warm gas tend to align in the simulated Milky Way with feedback from cosmic rays. Our study demonstrates that detailed, direct comparisons between simulations and observations, focused on gas kinematics, have the potential to reveal the dominant physical mechanisms that shape the CGM.

Additional Information

© 2022. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Received 2021 June 28; revised 2022 June 29; accepted 2022 July 4; published 2022 August 17. The authors thank Philip Hopkins, Suoqing Ji, Peng Oh, and the anonymous referee for their insightful comments. I.B. was supported by HST theory grant HST-AR-15046, the DuBridge Postdoctoral Fellowship from Caltech, and her tenure as a Blue Waters Graduate Fellow. The Blue Waters sustained-petascale computing project is supported by the National Science Foundation (grant No. OCI-0725070 and No. ACI-1238993) and the State of Illinois. J.K.W. acknowledges support as a Cottrell Scholar, from the Research Corporation for Science Advancement, grant ID number 26842. Additionally, J.K.W. and K.T. acknowledge support for this work from NSF-AST 1812521. D.B.F., through the Flatiron Institute, is supported by the Simons Foundation. This research benefited from the KITP Program: "Fundamentals of Gaseous Halos," and thus was supported in part by the National Science Foundation under grant No. NSF PHY-1748958.

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Published - Butsky_2022_ApJ_935_69.pdf

Submitted - 2106.14889.pdf

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Additional details

Created:
August 22, 2023
Modified:
October 24, 2023