Astrophysical interpretation of the anisotropies in the unresolved gamma-ray background

Ando, Shinʼichiro; Fornasa, Mattia; Fornengo, N.; Regis, Marco; Zechlin, H. S.

doi:10.1103/physrevd.95.123006

Cited by 21 publications

(23 citation statements)

References 75 publications

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“…We find that, while blazars dominate the resolved component of the extragalactic γ-ray background, as shown in Figure 3, SFGs dominate the unresolved component. This finding is consistent with statistical analyses of angular fluctuations in the isotropic background and cross-correlations between it and galaxies and quasars, which strongly disfavour blazars as a dominant contributor [4,7,37]. Indeed, a straightforward extrapolation of the number counts of observed blazars [38], illustrated by the orange band in Figure 3, also suggests that blazars do not dominate the unresolved background.…”

Section: Discussionsupporting

confidence: 83%

Star-forming galaxies dominate the diffuse, isotropic γ-ray background

Roth

Krumholz

Crocker

et al. 2020

Preprint

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The Fermi Gamma Ray Space Telescope has revealed a diffuse, isotropic γ-ray background at energies ranging from 0.1 GeV to 1 TeV [1] whose astrophysical sources remain uncertain. Previous efforts to understand the origin of this background have been hampered by the lack of physical models capable of predicting the γ-ray emission produced by the many candidate sources, which include star-forming galaxies (SFGs) [2–6], active galactic nuclei (particularly blazars [7–9]), millisecond pulsars[7], and dark matter annihilation [10]. In the absence of predictive models, estimates of the contribution from potential sources have relied on a highly-uncertain process of empirically scaling the emission from a small sample of local, resolved sources by their estimated cosmological abundances. Here we present the first calculation of the contribution of SFGs to the γ-ray background that is based on a physical model for the γ-ray emission produced when cosmic ray ions accelerated in supernova remnants interact with the interstellar medium [11]. We validate the model by showing that it reproduces the γ-ray spectra, source count distribution and far infrared-γ-ray correlation observed for nearby, resolved SFGs. When we apply the model to the observed cosmological SFG population, we recover an excellent match to the γ-ray background from 1 GeV to 1 TeV. Our result shows that SFGs alone can explain the full diffuse γ-ray background over this energy range, and strongly suggests that emission in excess of our model at energies <1 GeV originates from cosmic ray electrons produced in the same galaxies.

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Section: Discussionsupporting

confidence: 83%

Star-forming galaxies dominate the diffuse, isotropic γ-ray background

Roth

Krumholz

Crocker

et al. 2020

Preprint

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“…The SFG origin for this IGRB is strongly favored by the recent work of [20], whose method is based on a physical model for the gamma-ray emission with no free parameters (all quantities that are measured directly) rather than simple empirical scalings. In addition, the statistical analyses of angular fluctuations in the IGRB and cross-correlations between IGRB and galaxies also support the SFG origin [35,40]. Therefore, we model the astrophysical component in the IGRB below 5 GeV with the SFG contributions provided by [20].…”

Section: B the Flux From Extragalactic And Galactic Pbhsmentioning

confidence: 87%

Revisiting the constraints on primordial black hole abundance with the isotropic gamma ray background

Chen,

Zhang,

Long

2021

Preprint

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We revisit the constraints on primordial black holes (PBHs) in the mass range 10 13 − 10 18 g by comparing the 100 keV-5 GeV gamma-ray background with isotropic flux from PBH Hawking radiation (HR). We investigate three effects that may update the constraints on the PBH abundance; i) reliably calculating the secondary spectra of HR for energy below 5 GeV, ii) the contributions to the measured isotropic flux from the Galactic PBH HR and that from annihilation radiation due to evaporated positrons, iii) inclusion of astrophysical background from gamma-ray sources. The conservative constraint is significantly improved by more than an order of magnitude at 2 × 10 16 g M 10 17 g over the past relevant work, where the effect ii is dominant. After further accounting for the astrophysical background, more than a tenfold improvement extends to a much wider mass range 10 15 g M 2 × 10 17 g.

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“…The first detection of anisotropies in the UGRB was reported by the Fermi-LAT Collaboration in 2012 [25], and then updated in 2016, employing 81 months of Pass 7 Fermi LAT data from 0.5 to 500 GeV [26] (hereafter Fornasa et al). The latter analysis revealed a hint that the measured APS might be due to more than one population of sources [27].…”

Section: Introductionmentioning

confidence: 90%