Key Physical Processes in the Circumgalactic Medium

Faucher-Giguère, Claude-André; Oh, S. Peng

doi:10.1146/annurev-astro-052920-125203

Cited by 36 publications

(9 citation statements)

References 403 publications

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“…´-9 10 cm 16 2 (see also Liang & Remming 2020;Faucher-Giguere & Oh 2023). Therefore, the absence of components below N H = 10 17 cm −2 in Figure 2 can be understood as a result of this physical limit, rather than observational limitations.…”

Section: Possible Sample Selection Biasmentioning

confidence: 90%

The Cosmic Ultraviolet Baryon Survey: Empirical Characterization of Turbulence in the Cool Circumgalactic Medium

Chen,

Qu,

Rauch

et al. 2023

ApJL

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This paper reports the first measurement of the relationship between turbulent velocity and cloud size in the diffuse circumgalactic medium (CGM) in typical galaxy halos at redshift z ≈ 0.4–1. Through spectrally resolved absorption profiles of a suite of ionic transitions paired with careful ionization analyses of individual components, cool clumps of size as small as l cl ∼ 1 pc and density lower than n H = 10−3 cm−3 are identified in galaxy halos. In addition, comparing the line widths between different elements for kinematically matched components provides robust empirical constraints on the thermal temperature T and the nonthermal motions b NT, independent of the ionization models. On average, b NT is found to increase with l cl following b NT ∝ l cl 0.3 over three decades in spatial scale from l cl ≈ 1 pc to l cl ≈ 1 kpc. Attributing the observed b NT to turbulent motions internal to the clumps, the best-fit b NT–l cl relation shows that the turbulence is consistent with Kolmogorov at <1 kpc with a roughly constant energy transfer rate per unit mass of ϵ ≈ 0.003 cm2 s−3 and a dissipation timescale of ≲100 Myr. No significant difference is found between massive quiescent and star-forming halos in the sample on scales less than 1 kpc. While the inferred ϵ is comparable to what is found in C iv absorbers at high redshift, it is considerably smaller than observed in star-forming gas or in extended line-emitting nebulae around distant quasars. A brief discussion of possible sources to drive the observed turbulence in the cool CGM is presented.

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Section: Possible Sample Selection Biasmentioning

confidence: 90%

The Cosmic Ultraviolet Baryon Survey: Empirical Characterization of Turbulence in the Cool Circumgalactic Medium

Chen,

Qu,

Rauch

et al. 2023

ApJL

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“…This main gas reservoir records critical information about a galaxyʼs past and ongoing interactions with the surrounding environment. Due to the tenuous nature of the CGM, absorption spectroscopy using bright background sources-predominantly quasi-stellar objects (QSOs)-has been the main probe of gaseous halos, yielding sensitive constraints on gas density, temperature, metallicity, and ionization state (e.g., Chen 2017; Tumlinson et al 2017;Rudie et al 2019;Péroux & Howk 2020;Donahue & Voit 2022;Faucher-Giguère & Oh 2023).…”

Section: Introductionmentioning

confidence: 99%

An Ensemble Study of Turbulence in Extended QSO Nebulae at z ≈ 0.5–1

Chen,

Rauch

et al. 2024

ApJ

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Turbulent motions in the circumgalactic medium play a critical role in regulating the evolution of galaxies, yet their detailed characterization remains elusive. Using two-dimensional velocity maps constructed from spatially extended [O ii] and [O iii] emission, Chen et al. measured the velocity structure functions (VSFs) of four quasar nebulae at z ≈ 0.5–1.1. One of these exhibits a spectacular Kolmogorov relation. Here, we carry out an ensemble study using an expanded sample incorporating four new nebulae from three additional quasi-stellar object (QSO) fields. The VSFs measured for all eight nebulae are best explained by subsonic turbulence revealed by the line-emitting gas, which in turn strongly suggests that the cool gas (T ∼ 104 K) is dynamically coupled to the hot ambient medium. Previous work demonstrates that the largest nebulae in our sample reside in group environments with clear signs of tidal interactions, suggesting that environmental effects are vital in seeding and enhancing the turbulence within the gaseous halos, ultimately promoting the formation of the extended nebulae. No discernible differences are observed in the VSF properties between radio-loud and radio-quiet QSO fields. We estimate the turbulent heating rate per unit volume, Q turb, in the QSO nebulae to be ∼10−26–10−22 erg cm−3 s−1 for the cool phase and ∼10−28–10−25 erg cm−3 s−1 for the hot phase. This range aligns with measurements in the intracluster medium and star-forming molecular clouds but is ∼103 times higher than the Q turb observed inside cool gas clumps on scales ≲1 kpc using absorption-line techniques. We discuss the prospect of bridging the gap between emission and absorption studies by pushing the emission-based VSF measurements to below ≈10 kpc.

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“…Despite representing only a billionth of all particles in the Milky Way, CRs on a whole have as much energy as normal, non-relativistic gas [8], and it is clear from a veritable explosion of work in the last decade (e.g. [4,[9][10][11][12][13][14][15][16][17][18]) that the content of CRs in various astrophysical environments and the dynamical and thermodynamical influence of CRs on the surrounding gas sensitively depend on this transport. For example, in simulations of the Large Magellanic Cloud (LMC), a neighboring satellite galaxy of the Milky Way, if one allows CRs to stream, the galaxy remains largely intact over long periods of time as CRs easily lose pressure and escape the galaxy; however, if one replaces streaming with a small diffusivity instead, CRs build up a large pressure gradient in the galaxy and expel gas in a large-scale 'galactic wind' [19].…”

Section: Introduction 1cosmic Ray Fundamentalsmentioning

confidence: 99%

Deep learning cosmic ray transport from density maps of simulated, turbulent gas

Bustard,

2024

Mach. Learn.: Sci. Technol.

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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 transport of CRs along individual magnetic field lines -- for instance, diffusive vs streaming transport models -- is an unsolved challenge. Leveraging a recent training set of magnetohydrodynamic turbulent box simulations, with CRs spanning a range of transport parameters, we use convolutional neural networks (CNNs) trained solely on gas density maps to classify CR transport regimes. We find that even relatively simple CNNs can quite effectively classify density slices to corresponding CR transport parameters, distinguishing between streaming and diffusive transport, as well as magnitude of diffusivity, with class accuracies between 92% and 99%. As we show, the transport-dependent imprints that CRs leave on the gas are not all tied to the resulting density power spectra: classification accuracies are still high even when image spectra are flattened (85% to 98% accuracy), highlighting CR transport-dependent changes to turbulent phase information. We interpret our results with saliency maps and image modifications, and we discuss physical insights and future applications.

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Key Physical Processes in the Circumgalactic Medium

Cited by 36 publications

References 403 publications

The Cosmic Ultraviolet Baryon Survey: Empirical Characterization of Turbulence in the Cool Circumgalactic Medium

The Cosmic Ultraviolet Baryon Survey: Empirical Characterization of Turbulence in the Cool Circumgalactic Medium

An Ensemble Study of Turbulence in Extended QSO Nebulae at z ≈ 0.5–1

Deep learning cosmic ray transport from density maps of simulated, turbulent gas

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