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Cosmic rays (CRs) are a dynamically important component of the interstellar medium (ISM) of galaxies. The $\sim$GeV CRs that carry most CR energy and pressure are likely confined by self-generated turbulence, leading them to stream along…

Astrophysics of Galaxies · Physics 2022-11-16 Matt L. Sampson , James R. Beattie , Mark R. Krumholz , Roland M. Crocker , Christoph Federrath , Amit Seta

The microphysics of ~GeV cosmic ray (CR) transport on galactic scales remain deeply uncertain, with almost all studies adopting simple prescriptions (e.g. constant-diffusivity). We explore different physically-motivated, anisotropic,…

High Energy Astrophysical Phenomena · Physics 2022-03-18 Philip F. Hopkins , Jonathan Squire , T. K. Chan , Eliot Quataert , Suoqing Ji , Dusan Keres , Claude-Andre Faucher-Giguere

The observed bimodality in radio luminosity in galaxy clusters is puzzling. We investigate the possibility that cosmic-ray (CR) streaming in the intra-cluster medium can 'switch off' hadronically induced radio and gamma-ray emission. For…

High Energy Astrophysical Phenomena · Physics 2015-06-15 Joshua Wiener , S Peng Oh , Fulai Guo

Cosmic rays (CRs) may drive outflows and alter the phase structure of the circumgalactic medium, with potentially important implications on galaxy formation. However, these effects ultimately depend on the dominant mode of transport of CRs…

We explore the impact of diffusive cosmic rays (CRs) on the evolution of the interstellar medium (ISM) under varying assumptions of supernova explosion environment. In practice, we systematically vary the relative fractions of supernovae…

Astrophysics of Galaxies · Physics 2022-12-28 Christine M. Simpson , Rüdiger Pakmor , Christoph Pfrommer , Simon C. O. Glover , Rowan Smith

We aim to elucidate cosmic ray (CR) propagation in the weakly ionized environments of supernova remnants (SNRs) basing our analysis on the cosmic ray cloud (CRC) model developed by \citet{2013ApJ...768...73M} and…

High Energy Astrophysical Phenomena · Physics 2020-01-15 L. Brahimi , A. Marcowith , V. S. Ptuskin

We investigate how cosmic ray (CR) transport in molecular clouds and their substructures can be probed using multi-wavelength observations. The detailed microphysics regulating the penetration and coupling of CRs in dense molecular…

High Energy Astrophysical Phenomena · Physics 2026-05-19 Hayden P. H. Ng , Ellis R. Owen , Naomi Tsuji , Szu-Ting Chen

A major uncertainty in understanding the transport and feedback of cosmic-rays (CRs) within and beyond our Galaxy lies in the unknown CR scattering rates, which are primarily determined by wave-particle interaction at microscopic…

High Energy Astrophysical Phenomena · Physics 2022-04-06 Xue-Ning Bai

Cosmic rays (CRs) are ubiquitous in the interstellar medium (ISM) of nearby galaxies, but many of their properties are not well-constrained. Gamma-ray observations provide a powerful tool in this respect, allowing us to constrain both the…

High Energy Astrophysical Phenomena · Physics 2023-07-19 Maria Werhahn , Philipp Girichidis , Christoph Pfrommer , Joseph Whittingham

The circumgalactic medium (CGM) plays a critical role in galaxy evolution, influencing gas flows, feedback processes, and galactic dynamics. Observations show a substantial cold gas reservoir in the CGM, but the mechanisms driving its…

Astrophysics of Galaxies · Physics 2025-06-11 Matthias Weber , Timon Thomas , Christoph Pfrommer , Ruediger Pakmor

Cosmic rays (CRs) have recently re-emerged as attractive candidates for mediating feedback in galaxies because of their long cooling timescales. They can have energy densities comparable to the thermal gas, but do not suffer catastrophic…

Astrophysics of Galaxies · Physics 2017-01-25 Joshua Wiener , Christoph Pfrommer , S. Peng Oh

Understanding the cosmic ray (CR) ionization rate is crucial in order to simulate the dynamics of, and interpret the chemical species observed in molecular clouds. Calculating the CR ionization rate requires both accurate knowledge of the…

High Energy Astrophysical Phenomena · Physics 2019-07-10 Kedron Silsbee , Alexei V. Ivlev

The bulk propagation speed of GeV-energy cosmic rays is limited by frequent scattering off hydromagnetic waves. Most galaxy evolution simulations that account for this confinement assume the gas is fully ionized and cosmic rays are…

High Energy Astrophysical Phenomena · Physics 2021-06-09 Chad Bustard , Ellen G. Zweibel

The coarse-grained propagation of Galactic cosmic rays (CRs) is traditionally constrained by phenomenological models of Milky Way CR propagation fit to a variety of direct and indirect observables; however, constraining the fine-grained…

Astrophysics of Galaxies · Physics 2024-02-07 Chad Bustard , John Wu

We investigate the effects of cosmic ray (CR) dynamics on cold, dense clouds embedded in a hot, tenuous galactic halo. If the magnetic field does not increase too much inside the cloud, the local reduction in Alfv\'en speed imposes a…

High Energy Astrophysical Phenomena · Physics 2017-01-25 Joshua Wiener , S. Peng Oh , Ellen G. Zweibel

In the Milky Way, cosmic rays (CRs) are dynamically important in the interstellar medium, contribute to hydrostatic balance, and may help regulate star formation. However, we know far less about the importance of CRs in galaxies whose gas…

Astrophysics of Galaxies · Physics 2021-01-27 Roland M. Crocker , Mark R. Krumholz , Todd A. Thompson

Recent studies have suggested that low-energy cosmic rays (CRs) may be accelerated inside molecular clouds by the shocks associated with star formation. We use a Monte Carlo transport code to model the propagation of CRs accelerated by…

Cosmic rays are a fundamental source of ionization for molecular and diffuse clouds, influencing their chemical, thermal, and dynamical evolution. The amount of cosmic rays inside a cloud also determines the $\gamma$-ray flux produced by…

High Energy Astrophysical Phenomena · Physics 2015-06-17 G. Morlino , S. Gabici

Molecular clouds are complex magnetized structures, with variations over a broad range of length scales. Ionization in dense, shielded clumps and cores of molecular clouds is thought to be caused by charged cosmic rays (CRs). These CRs can…

Astrophysics of Galaxies · Physics 2021-07-27 Ellis R. Owen , Alvina Y. L. On , Shih-Ping Lai , Kinwah Wu

Cosmic ray (CR) transport and acceleration is essential for many astrophysical problems, e.g., CMB foreground, ionization of molecular clouds and all high energy phenomena. Recent advances in MHD turbulence call for revisions in the…

High Energy Astrophysical Phenomena · Physics 2011-12-06 Huirong Yan , A. Lazarian