Cosmic ray driven outflows to Mpc scales from <i>L</i>* galaxies

Hopkins, Philip F.; Chan, T. K.; Ji, Suoqing; Hummels, Cameron; Kereš, Dušan; Quataert, Eliot; Faucher-Giguère, Claude André

doi:10.1093/mnras/staa3690

Cited by 81 publications

(91 citation statements)

References 131 publications

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“…The case of particular interest is where CR pressure dominates over thermal pressure in the CGM. A simple analytic model for this regime is discussed in more detail in Hopkins et al (2020c), as well as Ji et al (2020) and Hopkins et al (2020a), so we only briefly review here. For a constant effective (angle-averaged) diffusivityκ which is large enough (κ 10 29 cm 2 s −1 ) and galaxy central gas densities which are low enough (e.g.…”

Section: In Cr-dominated Haloesmentioning

confidence: 99%

“…In short, a prominent, solid-angle covering virial shock is absent from CR-dominated haloes; the halo gas is cooler at a few 10 4 K with extended bipolar outflows. In contrast, shocks are prevalent in non-CR haloes around and within the virial radius which heats up the halo gas to the virial temperature; the halo is inflow-dominated, and outflows are sparse and trapped inside the virial radius (the latter point is discussed in details in Hopkins et al 2020a). Compared to the MHD+ case, the CR+ run shows highly anisotropic spatial structures (Qu & Bregman 2019).…”

Section: Figurementioning

confidence: 99%

“…3 shows the inflow/outflow radial velocities, mass fluxes and turbulent velocities. Hopkins et al (2020a) present a detailed study of the effect of CRs on outflows in these simulations, so we only briefly summarize outflows here (as they are relevant for some inflow behaviours). In MHD+, outflows are quasi-spherical; they have similar density compared to inflows but higher temperature/entropy/thermal pressure (especially outside ∼R vir ); and the outflow temperature, radial velocity, and mass flux all decline with increasing radius r. Outflow velocities are also subsonic and subvirial, and the outflows appear well mixed with inflows well inside of R vir .…”

Section: Properties Of Inflows and Outflowsmentioning

confidence: 99%

“…Ji et al (2020) found that in non-CR haloes of MW mass (∼10 12 M ), halo gas is primarily warm-hot ( 10 5 K) with highly anisotropic, thermal pressure-confined cool filaments embedded, while in CR pressure-dominated ones, halo gas is much cooler at a few 10 4 K, and the CR pressure-supported cool phase is diffuse and volume-filling over the entire haloes. The gas kinematics in CR-dominated haloes are further discussed in Hopkins et al (2020a) with an emphasis on outflows. This work will primarily focus on the impact of CRs on the properties of inflows, as well as its consequence for the formation of virial shocks and the thermal state of halo gas.…”

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confidence: 99%

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Virial shocks are suppressed in cosmic ray-dominated galaxy haloes

Kereš

Chan

et al. 2021

Monthly Notices of the Royal Astronomical Society

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We study the impact of cosmic rays (CRs) on the structure of virial shocks, using a large suite of high-resolution cosmological FIRE-2 simulations accounting for CR injection by supernovae. In Milky Way-mass, low-redshift (z ≲ 1−2) haloes, which are expected to form ‘hot haloes’ with slowly cooling gas in quasi-hydrostatic equilibrium (with a stable virial shock), our simulations without CRs do exhibit clear virial shocks. The cooler phase condensing out from inflows becomes pressure confined to overdense clumps, embedded in low-density, volume-filling hot gas with volume-weighted cooling time longer than inflow time. The gas thus transitions sharply from cool free-falling inflow, to hot and thermal-pressure supported at approximately the virial radius (≈Rvir), and the shock is quasi-spherical. With CRs, we previously argued that haloes in this particular mass and redshift range build up CR-pressure-dominated gaseous haloes. Here, we show that when CR pressure dominates over thermal pressure, there is no significant virial shock. Instead, inflowing gas is gradually decelerated by the CR pressure gradient and the gas is relatively subsonic out to and even beyond Rvir. Rapid cooling also maintains subvirial temperatures in the inflowing gas within ∼Rvir.

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Section: In Cr-dominated Haloesmentioning

confidence: 99%

Section: Figurementioning

confidence: 99%

Section: Properties Of Inflows and Outflowsmentioning

confidence: 99%

mentioning

confidence: 99%

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Virial shocks are suppressed in cosmic ray-dominated galaxy haloes

Kereš

Chan

et al. 2021

Monthly Notices of the Royal Astronomical Society

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“…One promising interpretation of the low densities of cool gas is that the CGM is supported by nonthermal cosmic-ray pressure. In recent years, cosmic rays have been invoked in galaxy simulations to launch winds (Ipavich 1975;Uhlig et al 2012;Booth et al 2013;Pakmor et al 2016;Simpson et al 2016;Ruszkowski et al 2017;Farber et al 2018;Hopkins et al 2021a), and thereby altering the ionization structure of the CGM (Salem et al 2016;Butsky & Quinn 2018;Ji et al 2020b;Buck et al 2020). Although the quantitative details of the predicted CGM structure depend on the invoked model of cosmic-ray transport (Butsky & Quinn 2018;Hopkins et al 2021b,d), which is still poorly constrained, many of these simulations predict a cosmic-ray-pressuresupported CGM around low-redshift L* galaxies.…”

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The Impact of Cosmic Rays on Thermal Instability in the Circumgalactic Medium

Butsky

Fielding

Hayward

et al. 2020

ApJ

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Large reservoirs of cold (∼10 4 K) gas exist out to and beyond the virial radius in the circumgalactic medium (CGM) of all types of galaxies. Photoionization modeling suggests that cold CGM gas has significantly lower densities than expected by theoretical predictions based on thermal pressure equilibrium with hot CGM gas. In this work, we investigate the impact of cosmic-ray physics on the formation of cold gas via thermal instability. We use idealized three-dimensional magnetohydrodynamic simulations to follow the evolution of thermally unstable gas in a gravitationally stratified medium. We find that cosmic-ray pressure lowers the density and increases the size of cold gas clouds formed through thermal instability. We develop a simple model for how the cold cloud sizes and the relative densities of cold and hot gas depend on cosmic-ray pressure. Cosmic-ray pressure can help counteract gravity to keep cold gas in the CGM for longer, thereby increasing the predicted cold mass fraction and decreasing the predicted cold gas inflow rates. Efficient cosmic-ray transport, by streaming or diffusion, redistributes cosmicray pressure from the cold gas to the background medium, resulting in cold gas properties that are in between those predicted by simulations with inefficient transport and simulations without cosmic rays. We show that cosmic rays can significantly reduce galactic accretion rates and resolve the tension between theoretical models and observational constraints on the properties of cold CGM gas.

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Cosmic ray feedback in galaxies and galaxy clusters

Ruszkowski,

Pfrommer

2023

Astron Astrophys Rev

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Understanding the physical mechanisms that control galaxy formation is a fundamental challenge in contemporary astrophysics. Recent advances in the field of astrophysical feedback strongly suggest that cosmic rays (CRs) may be crucially important for our understanding of cosmological galaxy formation and evolution. The appealing features of CRs are their relatively long cooling times and relatively strong dynamical coupling to the gas. In galaxies, CRs can be close to equipartition with the thermal, magnetic, and turbulent energy density in the interstellar medium, and can be dynamically very important in driving large-scale galactic winds. Similarly, CRs may provide a significant contribution to the pressure in the circumgalactic medium. In galaxy clusters, CRs may play a key role in addressing the classic cooling flow problem by facilitating efficient heating of the intracluster medium and preventing excessive star formation. Overall, the underlying physics of CR interactions with plasmas exhibit broad parallels across the entire range of scales characteristic of the interstellar, circumgalactic, and intracluster media. Here we present a review of the state-of-the-art of this field and provide a pedagogical introduction to cosmic ray plasma physics, including the physics of wave–particle interactions, acceleration processes, CR spatial and spectral transport, and important cooling processes. The field is ripe for discovery and will remain the subject of intense theoretical, computational, and observational research over the next decade with profound implications for the interpretation of the observations of stellar and supermassive black hole feedback spanning the entire width of the electromagnetic spectrum and multi-messenger data.

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Cosmic ray driven outflows to Mpc scales from L* galaxies

Cited by 81 publications

References 131 publications

Virial shocks are suppressed in cosmic ray-dominated galaxy haloes

Virial shocks are suppressed in cosmic ray-dominated galaxy haloes

The Impact of Cosmic Rays on Thermal Instability in the Circumgalactic Medium

Cosmic ray feedback in galaxies and galaxy clusters

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