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

Neven Tomičić, Annie Hughes, Kathryn Kreckel, Florent Renaud, Jérôme Pety, Eva Schinnerer, Toshiki Saito, Miguel Querejeta, Christopher M. Faesi, Santiago Garcia-Burillo

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We present the first spatially resolved (∼0.5 kpc) measurements of the molecular gas depletion time τ depl 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 τ depl, 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 τ depl of 1-1.5 dex across the disk of NGC 2276, with a further, abrupt drop in τ depl of ∼1 dex along the galaxy's western edge. The global τ depl in NGC 2776 is τdepl = 0.55 Gyr, consistent with literature measurements for the nearby galaxy population. Such a large range in τ depl on subkiloparsec scales has never previously been observed within an individual isolated or premerger system. When using a metallicity-dependent molecular gas conversion factor the variation decreases by 0.5 dex. We attribute the variation in τ depl 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.

Original languageEnglish
Article numberL38
JournalAstrophysical Journal Letters
Issue number2
Publication statusPublished - 2018 Dec 20

Subject classification (UKÄ)

  • Astronomy, Astrophysics and Cosmology


  • galaxies: individual (NGC 2276)
  • galaxies: ISM
  • galaxies: star formation


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