A 50 pc scale view of star formation efficiency across NGC 628

TL;DR

This study investigates star formation efficiency in NGC 628 across multiple scales, revealing short overlap phases between molecular clouds and HII regions, and finding longer depletion times than in the Milky Way.

Contribution

It provides the first detailed multi-scale analysis of star formation in NGC 628, combining ALMA and VLT/MUSE data to reveal the temporal evolution and physical drivers of star formation.

Findings

Molecular gas depletion times are 1-3 Gyr.

Weak correlation between gas and HII regions at 50 pc scale.

Few clouds and HII regions are in the overlap phase, with depletion times >1 Gyr.

Abstract

Star formation is a multi-scale process that requires tracing cloud formation and stellar feedback within the local (<kpc) and global galaxy environment. We present first results from two large observing programs on ALMA and VLT/MUSE, mapping cloud scales (1arcsec = 47pc) in both molecular gas and star forming tracers across 90 kpc^2 of the central disk of NGC 628 to probe the physics of star formation. Systematic spatial offsets between molecular clouds and HII regions illustrate the time evolution of star-forming regions. Using uniform sampling of both maps on 50-500 pc scales, we infer molecular gas depletion times of 1-3 Gyr, but also find the increase of scatter in the star formation relation on small scales is consistent with gas and HII regions being only weakly correlated at the cloud (50 pc) scale. This implies a short overlap phase for molecular clouds and HII regions, which we test by directly matching our catalog of 1502 HII regions and 738 GMCs. We uncover only 74 objects in the overlap phase, and we find depletion times >1 Gyr, significantly longer than previously reported for individual star-forming clouds in the Milky Way. Finally, we find no clear trends that relate variations in the depletion time observed on 500 pc scales to physical drivers (metallicity, molecular and stellar mass surface density, molecular gas boundedness) on 50 pc scales.