Two Orders of Magnitude Variation in the Star Formation Efficiency across the Premerger Galaxy NGC 2276

We present the first spatially resolved (∼0.5 kpc) measurements of the molecular gas depletion time τdepl across the disk of the interacting spiral galaxy NGC 2276, a system with an asymmetric morphology in various star formation rate (SFR) tracers. To estimate τdepl, we use new NOEMA observations of the 12CO(1–0) emission tracing the bulk molecular gas reservoir in NGC 2276, and extinction-corrected Hα measurements obtained with the PMAS/PPaK integral field unit for robust estimates of the SFR. We find a systematic decrease in τdepl of 1–1.5 dex across the disk of NGC 2276, with a further, abrupt drop in τdepl of ∼1 dex along the galaxy's western edge. The global τdepl in NGC 2776 is ${\tau }_{\mathrm{depl}}=0.55\,\mathrm{Gyr}$, consistent with literature measurements for the nearby galaxy population. Such a large range in τdepl on subkiloparsec scales has never previously been observed within an individual isolated or premerger system. When using a metallicity-dependent molecular gas conversion factor ${X}_{\mathrm{CO}}$ the variation decreases by 0.5 dex. We attribute the variation in τdepl to the influence of galactic-scale tidal forces and ram pressure on NGC 2276's molecular interstellar medium. Our observations add to the growing body of numerical and observational evidence that galaxy–galaxy interactions significantly modify the molecular gas properties and star-forming activity within galactic disks throughout the interaction, and not just during the final merger phase.