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| Main Authors: | , , |
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| Format: | Preprint |
| Published: |
2024
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| Subjects: | |
| Online Access: | https://arxiv.org/abs/2402.18638 |
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Table of Contents:
- Star-forming and starburst galaxies (SFGs and SBGs) are powerful emitters of non-thermal $γ$-rays and neutrinos, due to their intense phases of star-formation activity, which should confine high-energy Cosmic-Rays (CRs) inside their environments. In this paper, using the publicly-available \texttt{fermitools}, we analyse 15.3 years of $γ$-ray between $1-1000\, \rm GeV$ data for 70 sources, 56 of which were not previously detected. We find at~$4σ$ level an indication of $γ$-ray emission for other two SBGs, namely M 83 and NGC 1365. By contrast, we find that, even with the new description of background, the significance for the $γ$-ray emission of M 33~(initially reported as discovered) still stands at $\sim \, 4σ$ (as already reported by previous works). Along with previous findings, the flux of each detected source is consistent with a $\sim E^{-2.3/2.4}$ spectrum, compatible with the injected CR flux inferred for CRs in the Milky-Way. We notice that the correlation between the calorimetric fraction~$F_{\rm cal}$ of high-energy protons in SFGs and SBGs (the fraction of high-energy protons actually producing high-energy $γ$-rays and neutrinos) and the SFR is in accordance with the expected scaling relation for CR escape dominated by advection. We remark that undiscovered sources strongly constrain $F_{\rm cal}$ at 95\% CL, providing fundamental information when we interpret the results as common properties of SFGs and SBGs. Finally, we find that these sources might contribute $(12\pm 3)\%$ to the EGB, while the corresponding diffuse neutrino flux strongly depends on the spectral index distribution along the source class.