Constraints on cosmic rays population in the radio halo of the M87 galaxy from gamma-ray observations

We present results of our search for extended high-energy emission around the M87 galaxy, which is the central galaxy in the Virgo cluster. The M87 galaxy harbors extremely heavy supermassive black hole, $M_{BH}>4\times10^{9}~M_{\odot}$ and for the last $100$ Myr experiences a period of increased activity that resulted in formation of extended lobes, which are prominent radio- and X-ray sources. We perform a search in $13$ yr of the Fermi-LAT data in three energy bins: $0.1$–$1$, $1$–$10$, and $10$–$100$ GeV. No significant detection of extended emission was achieved in any bin, with weak indication of a signal (${\sim}\,2.5\sigma$) in the last bin ($10$–$100$ GeV). We used $\gamma$-ray observations to put limits on cosmic rays population in the lobes, constraining their fraction X in comparison to the thermal energy of the hot gas. Depending on the value of spectral index, for electrons $X_e<(0.1{-}0.2)$ and protons were constrained at $X_p<(0.2{-}0.5)$ level. We confirm that cosmic rays is a subdominant component of the lobes, which are dominated by thermal gas.