Gamma Rays as Probes of Cosmic-Ray Propagation and Interactions in Galaxies

Tibaldo, L.; Gaggero, Daniele; Martin, Pierrick

doi:10.3390/universe7050141

Cited by 47 publications

(27 citation statements)

References 390 publications

(472 reference statements)

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“…CR interactions lead to the deposition of momentum and energy in their host environment (e.g. Owen et al 2018;Tibaldo et al 2021). Thus, they can become important in controlling the evolution of galaxies.…”

Section: Introductionmentioning

confidence: 99%

The extragalactic $γ$-ray background: imprints from the physical properties and evolution of star-forming galaxy populations

Owen,

Kong,

Lee

2021

Preprint

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Star-forming galaxies (SFGs) are expected to harbour an abundant reservoir of cosmic rays (CRs). At GeV energies, these CRs can undergo hadronic interactions with interstellar gases to produce 𝛾-rays, and the unresolved 𝛾-ray emission from populations of SFGs form a component of the extragalactic 𝛾-ray background (EGB). In this work, we investigate the contribution to the 0.01 -50 GeV EGB from SFG populations located up to redshift 𝑧 = 3. We consider their redshift evolution and variations in their physical properties, and model how this affects their contribution to the EGB. We find this is dominated by starbursts, while the contribution from main sequence SFGs is marginal at all energies. We also demonstrate that most of the 𝛾-ray contribution from SFGs emanates from low mass galaxies, with over 80 per cent of the emission originating from galaxies with stellar masses below 10 8 M . We show that the EGB at different energies captures different stages of the evolution of the source galaxies. At 0.01 GeV, the emission is dominated by galaxies at the noon of cosmic star-formation, around 𝑧 ∼ 2, however higher energy 𝛾-rays are instead mainly contributed from low mass starburst populations at higher redshifts, ∼ 700 Myr earlier. The redshift distributions of the EGB sources at different energies imprint intensity signatures at different angular scales, allowing their contribution to be distinguished using analyses of small-scale EGB intensity anisotropies. We show that the EGB is sensitive to the evolution of low mass populations of galaxies, particularly around 𝑧 ∼ 2 − 2.5, and that it provides a new means to probe the engagement of CRs in these galaxies before and during the high noon of cosmic star-formation.

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Section: Introductionmentioning

confidence: 99%

The extragalactic $γ$-ray background: imprints from the physical properties and evolution of star-forming galaxy populations

Owen,

Kong,

Lee

2021

Preprint

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“…One strong argument for the Galactic origin comes from the detection of gamma rays: observations of the Galaxy revealed that the Galactic disk is gamma-ray bright, which is a clear indication of the interactions of CRs with interstallar medium (ISM) material and Galactic magnetic field in the disk, and that gamma rays roughly scale with the amount of material in the disk. Moreover, observations of the Large Magellanic Cloud (LMC), located in the vicinity of our Galaxy at ∼50 kpc, have shown that the gamma-ray signal is weaker than expected given the mass of the target material in the LMC [2,3]. This reduced gamma-ray signal from the LMC can be seen as evidence that CRs are not homogeneously distributed in the Universe, and originate within our Galaxy.…”

Section: Introduction 1the Hunt For the Sources Of Galactic Cosmic Raysmentioning

confidence: 72%

The Hunt for Pevatrons: The Case of Supernova Remnants

Cristofari

2021

Universe

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The search for Galactic pevatrons is now a well-identified key science project of all instruments operating in the very-high-energy domain. Indeed, in this energy range, the detection of gamma rays clearly indicates that efficient particle acceleration is taking place, and observations can thus help identify which astrophysical sources can energize particles up to the ~PeV range, thus being pevatrons. In the search for the origin of Galactic cosmic rays (CRs), the PeV range is an important milestone, since the sources of Galactic CRs are expected to accelerate PeV particles. This is how the central scientific goal that is ’solving the mystery of the origin of CRs’ has often been distorted into ’finding (a) pevatron(s)’. Since supernova remnants (SNRs) are often cited as the most likely candidates for the origin of CRs, ’finding (a) pevatron(s)’ has often become ’confirming that SNRs are pevatrons’. Pleasingly, the first detection(s) of pevatron(s) were not associated to SNRs. Moreover, all clearly detected SNRs have yet revealed to not be pevatrons, and the detection from VHE gamma rays from regions unassociated with SNRs, are reminding us that other astrophysical sites might well be pevatrons. This short review aims at highlighting a few important results on the search for Galactic pevatrons.

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“…This implies a significant change in the energy behavior of the diffuse spectrum from to at TeV energies. With the emerging Cherenkov Telescope Array (CTA) [ 63 ] and its use of more than a hundred IACTs in the Northern and Southern Hemispheres, the background will be reduced and the field of view increased to , while improving sensitivity by an order of magnitude compared to current observatories consisting of only a few ground-based Imaging Air Cherenkov Telescopes (IACTs) [ 64 ]. These enhancements from diffuse measurements of the inner Galaxy with CTA, once available, will allow verification of our model.…”

Section: Discussion In the Astrophysical Contextmentioning

confidence: 99%

Regimes of cosmic-ray diffusion in Galactic turbulence

et al. 2021

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Cosmic-ray transport in astrophysical environments is often dominated by the diffusion of particles in a magnetic field composed of both a turbulent and a mean component. This process, which is two-fold turbulent mixing in that the particle motion is stochastic with respect to the field lines, needs to be understood in order to properly model cosmic-ray signatures. One of the most important aspects in the modeling of cosmic-ray diffusion is that fully resonant scattering, the most effective such process, is only possible if the wave spectrum covers the entire range of propagation angles. By taking the wave spectrum boundaries into account, we quantify cosmic-ray diffusion parallel and perpendicular to the guide field direction at turbulence levels above 5% of the total magnetic field. We apply our results of the parallel and perpendicular diffusion coefficient to the Milky Way. We show that simple purely diffusive transport is in conflict with observations of the inner Galaxy, but that just by taking a Galactic wind into account, data can be matched in the central 5 kpc zone. Further comparison shows that the outer Galaxy at $$>5$$ > 5 kpc, on the other hand, should be dominated by perpendicular diffusion, likely changing to parallel diffusion at the outermost radii of the Milky Way.

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Gamma Rays as Probes of Cosmic-Ray Propagation and Interactions in Galaxies

Cited by 47 publications

References 390 publications

The extragalactic $γ$-ray background: imprints from the physical properties and evolution of star-forming galaxy populations

The extragalactic $γ$-ray background: imprints from the physical properties and evolution of star-forming galaxy populations

The Hunt for Pevatrons: The Case of Supernova Remnants

Regimes of cosmic-ray diffusion in Galactic turbulence

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