A Classification Scheme for Young Stellar Objects Using the WIDE-FIELD INFRARED SURVEY EXPLORER AllWISE Catalog: Revealing Low-Density Star Formation in the Outer Galaxy

TL;DR

This paper develops a new classification scheme for young stellar objects using WISE and 2MASS data, revealing that most star formation occurs in massive regions with minimal isolated star formation in the outer Galaxy.

Contribution

It introduces a revised classification method for young stars combining infrared data and assesses star formation modes in the Outer Galaxy.

Findings

Most stars form in massive star-forming regions.

Isolated star formation is a minor component.

Star formation aligns with molecular cloud collapse models.

Abstract

We present an assessment of the performance of WISE and the AllWISE data release in a section of the Galactic Plane. We lay out an approach to increasing the reliability of point source photometry extracted from the AllWISE catalog in Galactic Plane regions using parameters provided in the catalog. We use the resulting catalog to construct a new, revised young star detection and classification scheme combining WISE and 2MASS near and mid-infrared colors and magnitudes and test it in a section of the Outer Milky Way. The clustering properties of the candidate Class I and II stars using a nearest neighbor density calculation and the two-point correlation function suggest that the majority of stars do form in massive star forming regions, and any isolated mode of star formation is at most a small fraction of the total star forming output of the Galaxy. We also show that the isolated component may be very small and could represent the tail end of a single mechanism of star formation in line with models of molecular cloud collapse with supersonic turbulence and not a separate mode all to itself.