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

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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.


  • Neven Tomičić
  • Annie Hughes
  • Kathryn Kreckel
  • Florent Renaud
  • Jérôme Pety
  • Eva Schinnerer
  • Toshiki Saito
  • Miguel Querejeta
  • Christopher M. Faesi
  • Santiago Garcia-Burillo
External organisations
  • Max Planck Institute for Astronomy
  • University of Toulouse
  • Centre d'Ecologie Fonctionnelle et Evolutive (CEFE)
  • European Southern Observatory
  • Institut de Radioastronomie Millimétrique IRAM
  • Royal Observatory of Madrid
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Astronomy, Astrophysics and Cosmology


  • galaxies: individual (NGC 2276), galaxies: ISM, galaxies: star formation
Original languageEnglish
Article numberL38
JournalAstrophysical Journal Letters
Issue number2
Publication statusPublished - 2018 Dec 20
Publication categoryResearch