Circum-Galactic Gas and the Isotropic Gamma-Ray Background

Feldmann, Robert; Hooper, Dan; Gnedin, Nickolay Y.

doi:10.1088/0004-637x/763/1/21

Cited by 82 publications

(109 citation statements)

References 75 publications

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“…The Milky Way and other disc galaxies can also be immersed into extended cosmic-ray (CR) halos (De Paolis et al 1999;Feldmann et al 2013). It is well known that the Milky Way is not a perfect calorimeter for proton CRs: they rather quickly, on time scales of 10-20 ⋆ E-mail: pshirkov@sai.msu.ru † E-mail: vasilyev@mpia.de ‡ E-mail: pk@sai.msu.ru Myr, escape from dense regions of the Galaxy, losing only minor part of their energy in interactions with the interstellar medium (Strong et al 2007(Strong et al , 2010.…”

Section: Introductionmentioning

confidence: 99%

“…The size and shape of the halo cannot be firmly established and depend crucially on the propagation properties of CRs. The halo 'half-light' radius is estimated to be 20-40 kpc (Feldmann et al 2013). At smaller scales (∼ 10 kpc), the gamma-ray halo can be non-uniform as evidenced by the 'Fermi bubbles' (FB) in the Galaxy (Su et al 2010;Ackermann et al 2014).…”

Section: Introductionmentioning

confidence: 99%

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Evidence of Fermi bubbles around M31

Пширков

Vasiliev

Постнов

2016

Monthly Notices of the Royal Astronomical Society: Letters

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Gamma-ray haloes can exist around galaxies due to the interaction of escaping galactic cosmic rays with the surrounding gas. We have searched for such a halo around the nearby giant spiral Andromeda galaxy M31 using almost 7 years of Fermi LAT data at energies above 300 MeV. The presence of a diffuse gamma-ray halo with total photon flux 2.6 ± 0.6 × 10 −9 cm −2 s −1 , corresponding to a luminosity (0.3-100 GeV) of (3.2±0.6)×1038 erg s −1 (for a distance of 780 kpc) was found at a 5.3σ confidence level. The halo form does not correspond to the extended baryonic HI disc of M31, as would be expected in hadronic production of gamma photons from cosmic ray interaction, nor it is spherically symmetric, as could be in the case of dark matter annihilation. The best-fit halo template corresponds to two 6-7.5 kpc bubbles symmetrically located perpendicular to the M31 galactic disc, similar to the 'Fermi bubbles' found around the Milky Way centre, which suggests the past activity of the central supermassive black hole or a star-formation burst in M31.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Evidence of Fermi bubbles around M31

Пширков

Vasiliev

Постнов

2016

Monthly Notices of the Royal Astronomical Society: Letters

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“…As motivated on theoretical (e.g. [17]) and observational (e.g. [11]) grounds, we adopt a constant gas density within the Bubbles at the level 3 × 10 −3 cm −3 .…”

Section: Pos(icrc2017)870mentioning

confidence: 99%

A Hadronic Model of the Fermi Bubbles: Cosmic-Rays in a Galactic Breeze

Giacinti

Taylor

2017

Proceedings of 35th International Cosmic Ray Conference — PoS(ICRC2017)

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We present a self-consistent model of the Fermi Bubbles, described as a decelerating outflow of gas and non-thermal particles produced within the Galactic center region, on a ∼ 100 Myr timescale. Motivated by observations, we use an outflow with velocity of a few hundreds of km/s, which is slower than the velocities used in models describing the Bubbles as a more recent outburst. We take into account cosmic-ray (CR) energy losses due to proton-proton interactions, and calculate the resulting gamma-ray emission. Our model can reproduce both the spatial morphology and the spectra of the Bubbles, on a range of different scales. We find that CR diffusing and advecting within a breeze outflow result in an approximately flat surface brightness profile of the gamma-ray emission, as observed by Fermi satellite. Finally, we apply similar outflow profiles to larger Galactocentric radii, and investigate their effects on the CR spectrum and boron-to-carbon ratio. Hardenings can appear in the spectrum, even in cases with equal CR diffusion coefficients in the disk and halo. It is postulated that this hardening effect may relate to the observed hardening feature in the CR spectrum at a rigidity of ∼ 200 GV.

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“…As motivated on theoretical grounds by [37], and on observational grounds by [11], we adopt a constant gas density within the bubble region at the level 3 × 10 −3 cm −3 . A γ-ray density map and a comparison of the γ-ray bubble-edge profile with Fermi measurement [38] are shown in Fig.…”

Section: Introductionmentioning

confidence: 99%

Cosmic rays in a galactic breeze

Taylor

Giacinti

2017

Phys. Rev. D

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Motivated by the discovery of the non-thermal Fermi bubble features both below and above the Galactic plane, we investigate a scenario in which these bubbles are formed through Galactocentric outflow. Cosmic rays (CR) both diffusing and advecting within a Galactic breeze outflow, interacting with the ambient gas present, give rise to γ-ray emission, providing an approximately flat surface brightness profile of this emission, as observed. Applying the same outflow profile further out within the disk, the resultant effects on the observable CR spectral properties are determined. A hardening in the spectra due to the competition of advective and diffusive propagation within a particular energy range is noted, even in the limiting case of equal CR diffusion coefficients in the disk and halo. It is postulated that this hardening effect may relate to the observed hardening feature in the CR spectrum at a rigidity of ≈ 200 GV.

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Circum-Galactic Gas and the Isotropic Gamma-Ray Background

Cited by 82 publications

References 75 publications

Evidence of Fermi bubbles around M31

Evidence of Fermi bubbles around M31

A Hadronic Model of the Fermi Bubbles: Cosmic-Rays in a Galactic Breeze

Cosmic rays in a galactic breeze

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