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

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 ($>100\mathrm{M}\mathrm{e}\mathrm{V}$) photon flux of $2.3\times {10}^{-9}\mathrm{p}\mathrm{h}\mathrm{c}{\mathrm{m}}^{-2}{\mathrm{s}}^{-1}$, 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.