Simulating Gamma-Ray Emission in Star-forming Galaxies

Pfrommer, Christoph; Pakmor, Rüdiger; Simpson, Christine M.; Springel, Volker

doi:10.3847/2041-8213/aa8bb1

Cited by 68 publications

(89 citation statements)

References 41 publications

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“…Our result suggests that most CRs escape before significant collisional losses in low-SFR galaxies, mainly through the diffusion process. This is consistent with the findings in some recent numerical simulations (Pfrommer et al 2017;Chan et al 2018). Fig.…”

Section: Discussionsupporting

confidence: 94%

Interpreting the Relation between the Gamma-Ray and Infrared Luminosities of Star-forming Galaxies

Zhang

Peng

Wang

2019

ApJ

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It has been found that there is a quasi-linear scaling relationship between the gamma-ray luminosity in GeV energies and the total infrared luminosity of star-forming galaxies, i.e. L γ ∝ L α IR with α ≃ 1. However, the origin of this linear slope is not well understood. Although extreme starburst galaxies can be regarded as calorimeters for hadronic cosmic ray interaction and thus a quasi-linear scaling may hold, it may not be the case for low star-formation-rate (SFR) galaxies, as the majority of cosmic rays in these galaxies are expected to escape. We calculate the gammaray production efficiency in star-forming galaxies by considering realistic galaxy properties, such as the gas density and galactic wind velocity in star-forming galaxies. We find that the slope for the relation between gamma-ray luminosity and the infrared luminosity gets steeper for low infrared luminosity galaxies, i.e. α → 1.6, due to increasingly lower efficiency for the production of gamma-ray emission. We further find that the measured data of the gamma-ray luminosity is compatible with such a steepening. The steepening in the slope suggests that cosmic-ray escape is very important in low-SFR galaxies.

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Section: Discussionsupporting

confidence: 94%

Interpreting the Relation between the Gamma-Ray and Infrared Luminosities of Star-forming Galaxies

Zhang

Peng

Wang

2019

ApJ

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“…fusion coefficient simulations. In accordance with previous work (Pfrommer et al 2017b;Girichidis et al 2018;Chan et al 2019;Hopkins et al 2020), we find that the hadronic and Coulomb cooling rate is higher for lower diffusion and the two streaming solutions. The reason is that CR energy spends more time in dense regions where the hadronic and Coulomb CR cooling rate is higher (it scales linearly with gas density), as shown in Fig.…”

Section: Fate Of the Cosmic Ray Energysupporting

confidence: 93%

Cosmic ray feedback from supernovae in dwarf galaxies

Dashyan

Dubois

2020

A&A

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The regulation of the baryonic content in dwarf galaxies is a long-standing problem. Supernovae (SNe) are supposed to play a key role in forming large-scale galactic winds by removing important amounts of gas from galaxies. SNe are efficient accelerators of non-thermal particles, so-called cosmic rays (CRs), which can substantially modify the dynamics of the gas and conditions to form large-scale galactic winds. We investigate how CR injection by SNe impacts the star formation and the formation of large-scale winds in dwarf galaxies, and whether it can produce galaxy star formation rates (SFR) and wind properties closer to observations. We run CR magneto-hydrodynamical simulations of dwarf galaxies at high resolution (9 pc) with the adaptive mesh refinement code ramses. Those disc galaxies are embedded in isolated halos of mass 10 10 and 10 11 M , and CRs are injected by SNe. We include CR isotropic and anisotropic diffusion with various diffusion coefficients, CR radiative losses, and CR streaming.The injection of CR energy into the interstellar medium smooths out the highest gas densities, which reduces the SFR by a factor of 2-3. Mass outflow rates are significantly greater with CR diffusion, by 2 orders of magnitudes for the higher diffusion coefficients. Without diffusion and streaming, CRs are inefficient at generating winds. CR streaming alone allows for the formation of winds but which are too weak to match observations. The formation of galactic winds strongly depends on the diffusion coefficient: for low coefficients, CR energy stays confined in high density regions where CR energy losses are highest, and higher coefficients, which allow for a more efficient leaking of CRs out of dense gas, produce stronger winds. CR diffusion leads to colder and denser winds than without CRs, and brings outflow rates and mass loading factors much closer to observations.

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“…qualitative behaviors ofĖ Ad in both dwarf and MW-mass systems in Pfrommer et al (2017b) are similar to what we find here. However, for the reasons discussed in § 5.1.2, our results do not support their conclusion that adiabatic losses are the dominant factor for the low Lγ/LSF in dwarfs.…”

Section: Cr Energetics and The Importance Ofsupporting

confidence: 87%

“…Instead, we simply assume a constant κ, which is a common approach in the literature (e.g. Booth et al 2013;Pakmor et al 2016;Pfrommer et al 2017b;Wiener et al 2017), and test a wide range of κ.…”

Section: The Diffusion Coefficientmentioning

confidence: 99%

“…Recently, Pfrommer et al (2017b) also investigated γ-ray emission with idealized galaxy simulations, assuming CR transport via either advection-only or advec-tion+anisotropic diffusion with κ = 10 28 cm 2 s −1 . They argued they could (a) reproduce the FIR-γ-ray correlation and (b) explain the low Lγ in non-starburst galaxies primarily by adiabatic losses.…”

Section: γ-Ray Emissionmentioning

confidence: 99%

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Cosmic ray feedback in the FIRE simulations: constraining cosmic ray propagation with GeV γ-ray emission

Chan

Kereš

Hopkins

et al. 2019

Monthly Notices of the Royal Astronomical Society

172

198

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ABSTRACT We present the implementation and the first results of cosmic ray (CR) feedback in the Feedback In Realistic Environments (FIRE) simulations. We investigate CR feedback in non-cosmological simulations of dwarf, sub-L⋆ starburst, and L⋆ galaxies with different propagation models, including advection, isotropic, and anisotropic diffusion, and streaming along field lines with different transport coefficients. We simulate CR diffusion and streaming simultaneously in galaxies with high resolution, using a two-moment method. We forward-model and compare to observations of γ-ray emission from nearby and starburst galaxies. We reproduce the γ-ray observations of dwarf and L⋆ galaxies with constant isotropic diffusion coefficient $\kappa \sim 3\times 10^{29}\, {\rm cm^{2}\, s^{-1}}$. Advection-only and streaming-only models produce order of magnitude too large γ-ray luminosities in dwarf and L⋆ galaxies. We show that in models that match the γ-ray observations, most CRs escape low-gas-density galaxies (e.g. dwarfs) before significant collisional losses, while starburst galaxies are CR proton calorimeters. While adiabatic losses can be significant, they occur only after CRs escape galaxies, so they are only of secondary importance for γ-ray emissivities. Models where CRs are ‘trapped’ in the star-forming disc have lower star formation efficiency, but these models are ruled out by γ-ray observations. For models with constant κ that match the γ-ray observations, CRs form extended haloes with scale heights of several kpc to several tens of kpc.

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Simulating Gamma-Ray Emission in Star-forming Galaxies

Cited by 68 publications

References 41 publications

Interpreting the Relation between the Gamma-Ray and Infrared Luminosities of Star-forming Galaxies

Interpreting the Relation between the Gamma-Ray and Infrared Luminosities of Star-forming Galaxies

Cosmic ray feedback from supernovae in dwarf galaxies

Cosmic ray feedback in the FIRE simulations: constraining cosmic ray propagation with GeV γ-ray emission

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