The Effect of Spiral Arms on Star Formation in the Galaxy

TL;DR

This study investigates how spiral arms influence star formation in the Galaxy, finding that most observed increases are due to source crowding and local effects, with some regions showing enhanced efficiency or luminosity.

Contribution

It provides a detailed analysis of star formation rate variations across spiral arms, highlighting the roles of source crowding, efficiency, and exceptional regions like W49.

Findings

60-80% of star formation increase due to source crowding

Inner Sagittarius arm shows increased star-formation efficiency

W49 complex causes a top-heavy IMF in the Perseus arm

Abstract

We have examined the ratio between the integrated luminosity of massive young stellar objects detected by the Red MSX Source (RMS) survey and the mass of molecular clouds in the Galactic Ring Survey region, as a function of Galactocentric radius. The results indicate that 60--80% of the observed increases in the star-formation rate density associated with spiral-arm features are due to source crowding within the arms. Of the remainder, most of the increase in the inner Sagittarius arm is due to an enhancement in the simple star-formation efficiency, i.e. in the number of RMS sources per unit molecular gas mass. In the inner Perseus arm, the residual increase is due to a higher than average mean source luminosity, which implies a top-heavy IMF, and this is entirely due to the presence, in the GRS region, of the W49 star-forming complex, which appears to be exceptional in its nature. The results also suggest that there is little or no increase in the star-formation efficiency on kiloparsec scales in the Scutum tangent region which includes W43. We discuss the possible role played by the spiral arms in influencing the star-formation efficiency and conclude that the most likely mechanisms are related to orbit crowding within the arms.