Cosmic ray-driven galactic winds: transport modes of cosmic rays and Alfvén-wave dark regions

Thomas, Timon; Pfrommer, Christoph; Pakmor, Rüdiger

doi:10.48550/arxiv.2203.12029

Cited by 7 publications

(6 citation statements)

References 76 publications

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“…Assuming r 0 ≈ 20 kpc and B 0 ≈ 5 µG, the ordered field strength would be the correct strength at r = 50 kpc. Such high magnetic field strengths are indeed seen in simulations (Pakmor et al 2020;Thomas et al 2022). One can also explain the higher polar RRM with a specific chimney structure, such as seen in simulations, where one would expect β ≈ 1 from the shear between chimneys and halo gas (Rodgers-Lee et al 2019;Krause et al 2021).…”

Section: Discussionsupporting

confidence: 55%

“…Similarly, if the gaseous halo of a galaxy hosts a dynamo, one would have large-scale magnetic field configurations (Moss et al 2010). Lastly, models of galactic winds show a helical magnetic field structure that results in a large-scale ordering (Zirakashvili et al 1996;Henriksen & Irwin 2016;Thomas et al 2022); such large-scale helical magnetic fields have indeed been found in galaxy haloes (Mora-Partiarroyo et al 2019;Stein et al 2020).…”

Section: Introductionmentioning

confidence: 97%

“…Two possible scenarios have been put forward to explain how the CGM might get magnetised: the magnetic fields are either generated in situ by turbulence via the small-scale dynamo (Pakmor et al 2017) or they are transported from the galaxies via galactic winds (Péroux et al 2020). Both models suggest that higher magnetic field strengths are found near the minor axis of galaxies as outflows, either stellar- (Thomas et al 2022) or active-galactic-nucleus-driven (Pillepich et al 2021), and are driven most easily along the minor axis, which both transports magnetic fields and generates turbulence. The processes that magnetise the CGM will also influence its structure.…”

Section: Introductionmentioning

confidence: 99%

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Detection of magnetic fields in the circumgalactic medium of nearby galaxies using Faraday rotation

Heesen¹,

O’Sullivan²,

Brüggen³

et al. 2023

A&A

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Context. The existence of magnetic fields in the circumgalactic medium (CGM) is largely unconstrained. Their detection is important as magnetic fields can have a significant impact on the evolution of the CGM, and, in turn, the fields can serve as tracers for dynamical processes in the CGM. Aims. Using the Faraday rotation of polarised background sources, we aim to detect a possible excess of the rotation measure in the surrounding area of nearby galaxies. Methods. We used 2,461 residual rotation measures (RRMs) observed with the LOw Frequency ARray (LOFAR), where the foreground contribution from the Milky Way is subtracted. The RRMs were then studied around a subset of 183 nearby galaxies that was selected by apparent B-band magnitude.Results. We find that, in general, the RRMs show no significant excess for small impact parameters (i.e. the perpendicular distance to the line of sight). However, if we only consider galaxies at higher inclination angles and sightlines that pass close to the minor axis of the galaxies, we find significant excess at impact parameters of less than 100 kpc. The excess in |RRM| is 3.7 rad m −2 with an uncertainty between ±0.9 rad m −2 and ±1.3 rad m −2 depending on the statistical properties of the background (2.8σ-4.1σ). With electron densities of ∼10 −4 cm −3 , this suggests magnetic field strengths of a few tenths of a microgauss. Conclusions. Our results suggest a slow decrease in the magnetic field strength with distance from the galactic disc, as expected if the CGM is magnetised by galactic winds and outflows.

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Section: Discussionsupporting

confidence: 55%

Section: Introductionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Detection of magnetic fields in the circumgalactic medium of nearby galaxies using Faraday rotation

Heesen¹,

O’Sullivan²,

Brüggen³

et al. 2023

A&A

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“…The codes use different approximations to solve the CR transport equation, but Chan et al (2019) have checked in their Appendix B3 that the impact on the SFR and γ-ray luminosities is small. Thomas et al (2022) also conclude that solving the two-moment expansion might be more important for CR transport in the winds, but not necessarily in the ISM, since the steady-state approximation holds within the galactic disc.…”

Section: Comparison With Other Simulationsmentioning

confidence: 85%

Cosmic-ray diffusion and the multi-phase interstellar medium in a dwarf galaxy. I. Large-scale properties and $γ$-ray luminosities

Nuñez-Castiñeyra,

Grenier,

Bournaud

et al. 2022

Preprint

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Context. Dynamically, cosmic rays with energies above about one GeV/nucleon may be important agents of galaxy evolution. Their pressure and pressure gradients compare with the thermal and magnetic ones to alter gas accretion onto a galaxy, drive fountains and massive galactic outflows, and alter the mass cycling between the diffuse gas reserves and the dense clouds where stars form. The feedback efficiency depends on the actual properties of cosmic-ray transport in the different media, so we crucially need theoretical clues and observational constraints on these properties in order to assess the impact of cosmic rays on galaxy evolution. Aims. We aim to study the dynamical role of cosmic rays in shaping the interstellar medium of a galaxy when changing their propagation mode. As a first step, we perform high-resolution simulations of the evolution of the same isolated galaxy and compare the impact of the simplest cosmic-ray transport assumption of uniform diffusion. We also compare the total γ-ray luminosity produced in the galaxy by hadronic interactions between cosmic rays and the gas as this observable encapsulates the convolution of the gas and cosmic-ray spatial distributions and it can be compared to Fermi LAT data. Methods. We have simulated the evolution of a gas-rich dwarf galaxy (∼10 11 M in total mass, forming about 1 M yr −1 of stars) with the magnetohydrodynamic adaptive-mesh-refinement code RAMSES, down to 9-pc resolution. Cosmic rays are advected by the gas and they diffuse either isotropically or preferentially along the magnetic field with uniform diffusion coefficients ranging from 3 × 10 27 to 10 29 cm 2 s −1 in order to bracket the average value inferred in the Milky Way. The simulations use gas cooling and heating functions that model the multiphasic structure of the gas down to a much lower resolution than used here. We have also updated the observational relation seen between the γ-ray luminosities and star-formation rates of galaxies using the latest detection and characterisations of Fermi LAT sources. Results. We focus this article on the impact of CR transport on the large-scale properties of the galaxy. We find that the radial and vertical distributions of the gas in the different phases, as well as the mass ranking between the phases, are marginally altered when changing cosmic-ray transport. We observe a positive feedback of cosmic rays on the amplification of the magnetic field in the inner half of the galaxy, except for fast isotropic diffusion. The increase in cosmic-ray pressure for slow or anisotropic diffusion can suppress star formation by up to 50%, but the dual effect of cosmic-ray pressure and magnetic amplification can reduce star formation by a factor 2.5. The global γ-ray luminosities and star-formation rates of the simulated galaxies are fully consistent with the best-fit trend seen in the observations in the case of anisotropic 10 27.5−29 cm 2 s −1 diffusion and for isotropic diffusion slower or equal to 3 × 10 28 cm 2 s −1 . These results therefore do not confirm clai...

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“…They can reach high energy densities in star forming regions, leading to equipartition with thermal gas (Boulares & Cox 1990), which, coupled with their ability to transfer energy and momentum to the gas, makes them an important component to be included in the ISM. They have indeed been shown to accelerate gas out of galactic discs, launching large scale outflows by creating a gradient of pressure pointing towards the disc (Breitschwerdt et al 1991;Uhlig et al 2012;Hanasz et al 2013;Booth et al 2013;Pakmor et al 2016;Dorfi et al 2019;Thomas et al 2022;Girichidis et al 2022). The implementation of comic rays in supernova feedback has led to interesting results for the outflows, as compared to purely thermal feedback.…”

Section: Introductionmentioning

confidence: 99%

The phase structure of cosmic ray driven outflows in stream fed disc galaxies

Peschken¹,

Hanasz²,

Naab³

et al. 2022

Preprint

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Feeding with gas in streams is predicted to be an important galaxy growth mechanism. Using an idealised setup, we study the impact of stream feeding (with 10 7 M Myr −1 rate) on the star formation and outflows of disc galaxies with ∼10 11 M baryonic mass. The magneto-hydrodynamical simulations are carried out with the piernik code and include star formation, feedback from supernova, and cosmic ray advection and diffusion. We find that stream accretion enhances galactic star formation. Lower angular momentum streams result in more compact discs, higher star formation rates and stronger outflows. In agreement with previous studies, models including cosmic rays launch stronger outflows travelling much further into the galactic halo. Cosmic ray supported outflows are also cooler than supernova only driven outflows. With cosmic rays, the star formation is suppressed and the thermal pressure is reduced. We find evidence for two distinct outflow phases. The warm outflows have high angular momentum and stay close to the galactic disc, while the hot outflow phase has low angular momentum and escapes from the centre deep into the halo. Cosmic rays can therefore have a strong impact on galaxy evolution by removing low angular momentum, possibly metal enriched gas from the disc and injecting it into the circumgalactic medium.

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Cosmic ray-driven galactic winds: transport modes of cosmic rays and Alfvén-wave dark regions

Cited by 7 publications

References 76 publications

Detection of magnetic fields in the circumgalactic medium of nearby galaxies using Faraday rotation

Detection of magnetic fields in the circumgalactic medium of nearby galaxies using Faraday rotation

Cosmic-ray diffusion and the multi-phase interstellar medium in a dwarf galaxy. I. Large-scale properties and $γ$-ray luminosities

The phase structure of cosmic ray driven outflows in stream fed disc galaxies

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