Search for the Gamma-ray Emission from M33 with Fermi LAT

TL;DR

This study searches for gamma-ray emission from galaxy M33 using Fermi LAT data but finds no significant signal, setting new upper limits that inform cosmic ray density estimates and align with star formation and gamma-ray luminosity correlations.

Contribution

First gamma-ray flux upper limit for M33 using Fermi LAT data, refining previous constraints and informing cosmic ray density estimates.

Findings

No significant gamma-ray emission detected from M33.

Established a new upper limit on gamma-ray flux of 2.3×10⁻⁹ ph cm⁻² s⁻¹.

Results consistent with star formation rate and gamma-ray luminosity correlation.

Abstract

In the work we search for the $\gamma$-ray signal from M33, one of the biggest galaxies in the Local Group, by using the Pass 8 data of Fermi Large Area Telescope (LAT). No statistically significant gamma-ray emission has been detected in the direction of M33 and we report a new upper limit of high energy ($>100\,\rm MeV$) photon flux of $2.3\times 10^{-9}\,\rm ph\,cm^{-2}\,s^{-1}$, which is more strict than previous constrains and implies a cosmic ray density of M33 lower than that speculated previously. Nevertheless the current limit is still in agreement with the correlation of star formation rate and $\gamma$-ray luminosity inferred from the Local group galaxies and a few nearby starburst galaxies.