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Two Orders of Magnitude Variation in the Star Formation Efficiency Across the Pre-Merger Galaxy NGC 2276

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Authors : Neven Tomicic, Annie Hughes, Kathryn Kreckel, Florent Renaud, Jerome Pety, Eva Schinnerer, Toshiki Saito, Miguel Querejeta, Christopher Faesi, Santiago Garcia-Burillo
Abstract : 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 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 τdepl=0.55 Gyr, insistent with literature measurements for the nearby galaxy population. Such a large range in τdepl on sub-kpc scales has never previously been observed within an individual isolated or pre-merger system. When using a metallicity-dependent molecular gas conversion factor XCO 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 (ISM). 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.
Journal : Astrophysical Journal ArXiv