New limit on high Galactic latitude PeV $\gamma$-ray flux from Tibet AS$\gamma$ data

Tibet AS-gamma collaboration has recently reported detection of gamma-rays with energies up to PeV from parts of the Galactic plane. We noticethat the analysis of gamma-ray flux by Tibet AS-gamma experiment also implies an upper bound on diffuse gamma-ray flux from high Galactic latitudes(|b|>20 degrees) in the energy range between 100 TeV and 1 PeV. This bound is up to an order-of-magnitude stronger than previously derived bounds from GRAPES3, KASCADE and CASA-MIA experiments. We discuss the new TibetAS-gamma limit on high Galactic latitude gamma-ray flux in the context of possible mechanisms of multi-messenger (gamma-ray and neutrino) emission from nearby cosmic ray sources, dark matter decays and large scale cosmic ray halo of the Milky Way.