The Diverse Stellar Populations of the W3 Star Forming Complex

TL;DR

This study uses Chandra X-ray observations to reveal diverse stellar populations in the W3 star forming complex, highlighting different formation mechanisms and spatial distributions of young stars and high-mass stars.

Contribution

It provides the first detailed X-ray view of the W3 complex, identifying three distinct stellar populations and proposing multiple star formation processes.

Findings

W3 Main hosts about 900 X-ray stars over 7 pc.

W3(OH) has ~50 PMS stars in a 0.6 pc region.

W3 North contains a massive star without accompanying PMS stars.

Abstract

An 800 sq-arcmin mosaic image of the W3 star forming complex obtained with the Chandra X-ray Observatory gives a valuable new view of the spatial structure of its young stellar populations. The Chandra image reveals about 1300 faint X-ray sources, most of which are PMS stars in the cloud. Some, but not all, of the high-mass stars producing hypercompact and ultracompact H II (UCHII) regions are also seen, as reported in a previous study. The Chandra images reveal three dramatically different embedded stellar populations. The W3 Main cluster extends over 7 pc with about 900 X-ray stars in a nearly-spherical distribution centered on the well-studied UCHII regions and high-mass protostars. The cluster surrounding the prototypical UCHII region W3(OH) shows a much smaller (<0.6 pc), asymmetrical, and clumpy distribution of about 50 PMS stars. The massive star ionizing the W3 North H II region is completely isolated without any accompanying PMS stars. In W3 Main, the inferred ages of the widely distributed PMS stars are significantly older than the inferred ages of the central OB stars illuminating the UCHIIs. We suggest that different formation mechanisms are necessary to explain the diversity of the W3 stellar populations: cluster-wide gravitational collapse with delayed OB star formation in W3 Main, collect-and-collapse triggering by shock fronts in W3(OH), and a runaway O star or isolated massive star formation in W3 North.