A Targeted Gamma-Ray Search of Five Prominent Galaxy Merger Systems with 17 years of Fermi-LAT Data

TL;DR

This study searches for gamma-ray emission from five galaxy mergers using 17 years of Fermi-LAT data, finding marginal signals in two systems and providing new insights into merger-driven star formation and cosmic ray acceleration.

Contribution

First targeted gamma-ray analysis of these five galaxy merger systems, constraining their emission and exploring the connection to star formation and cosmic rays.

Findings

Marginal gamma-ray detections in NGC 3256 and NGC 660.

Non-detections in the remaining systems.

Constraints on gamma-ray fluxes and spectral indices.

Abstract

Galaxy mergers are among the most energetic astrophysical phenomena, driving intense star formation and potentially fueling cosmic ray acceleration, which can produce high energy $\gamma$-ray emission through hadronic processes. We present a targeted search for $\gamma$-ray emission from five prominent galaxy merger systems, NGC~3256, NGC~660, UGC~813/816, UGC~12914/12915, and VV~114 using 16.9 years of Fermi-LAT data in the 1--300~GeV energy range. Employing a binned maximum likelihood analysis, we model the emission with power-law spectra and derive spectral energy distributions (SEDs) to constrain $\gamma$-ray fluxes and spectral indices. Marginal detections are found for NGC~3256 (TS = 15.4, $\sim$3.51$\sigma$) and NGC~660 (TS = 8.16, $\sim$2.39$\sigma$), with photon fluxes of $(7.21 \pm 3.17) \times 10^{-11}$ and $(8.28 \pm 3.56) \times 10^{-11}$ ph cm$^{-2}$ s$^{-1}$, respectively, suggesting merger driven star formation contributes to $\gamma$-ray emission. The remaining systems yield non-detections (TS $< 5$). This is the first targeted study of $\gamma$-ray emission from these aforementioned galaxy merger systems.