Evidence for Delayed Massive Star Formation in the M17 Proto-OB Association

TL;DR

This study identifies a large population of young stellar objects in the M17 SWex region, revealing delayed formation of massive stars and suggesting a different initial mass function than typical models.

Contribution

It provides evidence for delayed massive star formation in a proto-OB association, highlighting differences in the stellar initial mass function.

Findings

Over 1.3x10^4 young stars identified in M17 SWex.

Steeper YSO mass function than Salpeter IMF.

Absence of early O stars indicates delayed massive star formation.

Abstract

Through analysis of archival images and photometry from the Spitzer GLIMPSE and MIPSGAL surveys combined with 2MASS and MSX data, we have identified 488 candidate young stellar objects (YSOs) in the giant molecular cloud M17 SWex, which extends ~50 pc southwest from the prominent Galactic H II region M17. Our sample includes >200 YSOs with masses >3 Msun that will become B-type stars on the main sequence. Extrapolating over the stellar initial mass function (IMF), we find that M17 SWex contains >1.3x10^4 young stars, representing a proto-OB association. The YSO mass function is significantly steeper than the Salpeter IMF, and early O stars are conspicuously absent from M17 SWex. Assuming M17 SWex will form an OB association with a Salpeter IMF, these results reveal the combined effects of (1) more rapid circumstellar disk evolution in more massive YSOs and (2) delayed onset of massive star formation.