SEDIGISM-ATLASGAL: Dense Gas Fraction and Star Formation Efficiency Across the Galactic Disk

TL;DR

This study combines two large-scale surveys to analyze the distribution and efficiency of star formation in the Galactic disk, finding that spiral arms do not significantly enhance star formation efficiency but influence molecular cloud concentration.

Contribution

It provides a comprehensive analysis of dense gas fractions and star formation efficiencies across the Galactic disk using combined survey data, highlighting the limited role of spiral arms in star formation processes.

Findings

Molecular material is concentrated in spiral arms (~60%).

No significant variation in star formation efficiency near spiral arms.

Star formation activity is more influenced by local environment than spiral arm location.

Abstract

By combining two surveys covering a large fraction of the molecular material in the Galactic disk we investigate the role the spiral arms play in the star formation process. We have matched clumps identified by ATLASGAL with their parental GMCs as identified by SEDIGISM, and use these giant molecular cloud (GMC) masses, the bolometric luminosities, and integrated clump masses obtained in a concurrent paper to estimate the dense gas fractions (DGF$_{\rm gmc}=\sum M_{\rm clump}/M_{\rm gmc}$) and the instantaneous star forming efficiencies (i.e., SFE$_{\rm gmc} = \sum L_{\rm clump}/M_{\rm gmc}$). We find that the molecular material associated with ATLASGAL clumps is concentrated in the spiral arms ($\sim$60% found within $\pm$10 km s$^{-1}$ of an arm). We have searched for variations in the values of these physical parameters with respect to their proximity to the spiral arms, but find no evidence for any enhancement that might be attributable to the spiral arms. The combined results from a number of similar studies based on different surveys indicate that, while spiral-arm location plays a role in cloud formation and HI to H$_2$ conversion, the subsequent star formation processes appear to depend more on local environment effects. This leads us to conclude that the enhanced star formation activity seen towards the spiral arms is the result of source crowding rather than the consequence of a any physical process.