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| Main Authors: | , , , , , |
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| Format: | Preprint |
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2025
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| Online Access: | https://arxiv.org/abs/2511.13818 |
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| _version_ | 1866912715440652288 |
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| author | Doliya, Jaya Das, Deep Jyoti Bouri, Subhadip Bhattacharjee, Pooja Das, Mousumi Laha, Ranjan |
| author_facet | Doliya, Jaya Das, Deep Jyoti Bouri, Subhadip Bhattacharjee, Pooja Das, Mousumi Laha, Ranjan |
| contents | The origin and acceleration mechanism of cosmic rays (CRs) remain fundamental open questions. Galaxy mergers are proposed as very high-energy CR accelerators, which are expected to produce high-energy (HE) $γ$ rays and neutrinos through interactions with the ambient gas and low-energy background radiation fields. For the first time, we systematically study the HE $γ$-ray emission from galaxy mergers utilising 16.7 years of Fermi Large Area Telescope (Fermi-LAT) data with the sample list compiled from eight survey catalogs. Our analysis finds 8 galaxy mergers that exhibit $γ$-ray emission with significance $\gtrsim5σ$ in the 1-500 GeV energy range. A stacking analysis of the remaining faint galaxy mergers yields a combined $γ$-ray emission detected at $\sim 35σ$ significance, a best-fit spectral index of $Γ\approx 2.07$, and an energy flux of $\sim \rm 2\times10^{-14}~erg~cm^{-2}~s^{-1}$. We compare the stacked spectral energy distributions of the galaxy mergers with the projected sensitivity of the upcoming $γ$-ray telescope Cherenkov Telescope Array (CTA). Furthermore, we find that 18 previously unassociated Fermi-LAT sources are spatially coincident with galaxy mergers. Our findings establish galaxy mergers as a new class of HE $γ$-ray sources. Future neutrino and $γ$-ray observatories will be crucial to discover the particle acceleration mechanism in these newly identified CR sources. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2511_13818 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Galaxy Mergers Collectively Illuminate the $γ$-Ray Sky Doliya, Jaya Das, Deep Jyoti Bouri, Subhadip Bhattacharjee, Pooja Das, Mousumi Laha, Ranjan High Energy Astrophysical Phenomena The origin and acceleration mechanism of cosmic rays (CRs) remain fundamental open questions. Galaxy mergers are proposed as very high-energy CR accelerators, which are expected to produce high-energy (HE) $γ$ rays and neutrinos through interactions with the ambient gas and low-energy background radiation fields. For the first time, we systematically study the HE $γ$-ray emission from galaxy mergers utilising 16.7 years of Fermi Large Area Telescope (Fermi-LAT) data with the sample list compiled from eight survey catalogs. Our analysis finds 8 galaxy mergers that exhibit $γ$-ray emission with significance $\gtrsim5σ$ in the 1-500 GeV energy range. A stacking analysis of the remaining faint galaxy mergers yields a combined $γ$-ray emission detected at $\sim 35σ$ significance, a best-fit spectral index of $Γ\approx 2.07$, and an energy flux of $\sim \rm 2\times10^{-14}~erg~cm^{-2}~s^{-1}$. We compare the stacked spectral energy distributions of the galaxy mergers with the projected sensitivity of the upcoming $γ$-ray telescope Cherenkov Telescope Array (CTA). Furthermore, we find that 18 previously unassociated Fermi-LAT sources are spatially coincident with galaxy mergers. Our findings establish galaxy mergers as a new class of HE $γ$-ray sources. Future neutrino and $γ$-ray observatories will be crucial to discover the particle acceleration mechanism in these newly identified CR sources. |
| title | Galaxy Mergers Collectively Illuminate the $γ$-Ray Sky |
| topic | High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2511.13818 |