PHANGS-JWST First Results: Spurring on Star Formation: JWST Reveals Localised Star Formation in a Spiral Arm Spur of NGC 628

Abstract

We combine JWST observations with ALMA CO and VLT-MUSE H$\alpha$ data to examine off-spiral arm star formation in the face-on, grand-design spiral galaxy NGC 628. We focus on the northern spiral arm, around a galactocentric radius of 3-4 kpc, and study two spurs. These form an interesting contrast, as one is CO-rich and one CO-poor, and they have a maximum azimuthal offset in MIRI 21$\mu$m and MUSE H$\alpha$ of around 40${}^{\circ }$ (CO-rich) and 55${}^{\circ }$ (CO-poor) from the spiral arm. The star formation rate is higher in the regions of the spurs near to spiral arms, but the star formation efficiency appears relatively constant. Given the spiral pattern speed and rotation curve of this galaxy and assuming material exiting the arms undergoes purely circular motion, these offsets would be reached in 100-150 Myr, significantly longer than the 21$\mu$m and H$\alpha$ star formation timescales (both <10 Myr). The invariance of the star formation efficiency in the spurs versus the spiral arms indicates massive star formation is not only triggered in spiral arms, and cannot simply occur in the arms and then drift away from the wave pattern. These early JWST results show that in-situ star formation likely occurs in the spurs, and that the observed young stars are not simply the `leftovers' of stellar birth in the spiral arms. The excellent physical resolution and sensitivity that JWST can attain in nearby galaxies will well resolve individual star-forming regions and help us to better understand the earliest phases of star formation.

11 pages, 5 Figures, accepted as part of a PHANGS-JWST Focus Issue to appear in ApJ. Updated to include missing author and published paper references

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Cited by in corpus (10)

• The PHANGS-JWST Treasury Survey: Star Formation, Feedback, and Dust Physics at High Angular resolution in Nearby GalaxieS
• PHANGS-JWST First Results: A statistical view on bubble evolution in NGC628
• PHANGS--JWST First Results: ISM structure on the turbulent Jeans scale in four disk galaxies observed by JWST and ALMA
• The stellar population responsible for a kiloparsec size superbubble seen in the JWST "phantom" images of NGC628
• Resonance coupling in spiral arms: Patterns for flat rotation curve
• Dust around massive stars is agnostic to galactic environment: New insights from PHAT/BEAST
• Formation of filaments and feathers in disc galaxies: Is self-gravity enough?
• Revealing the Connection Between the Filamentary Hierarchy and Star Cluster Formation in a Simulated NGC 628 Galaxy
• Gravitational Torques from a Lopsided Young Stellar Component Sustain High Black Hole Accretion Rates in NGC 4593
• The Nuclear Star Cluster of M 74: a fossil record of the very early stages of a star-forming galaxy