Top: correlation between the gamma-ray luminosity L _γ (0.1–5 GeV) and the product of SFR and gas mass, ψ M _gas. The solid line represents the best fit power-law L _γ ∝ (ψ M _gas) ^α with α taken as a free parameter. The dashed line represents a linear function fit with a fixed value of α = 1. Bottom: the same as the top panel, but for the correlation between L _γ and SFR.