M33 massive young stellar objects

The Probabilistic Random Forest (PRF) methodology, previously applied to populations in NGC 6822, utilizes both near and far-IR classification features. It classifies sources into nine target classes: young stellar objects (YSOs), oxygen, and carbon-rich asymptotic giant branch stars, red giant branch, and red super-giant stars, active galactic nuclei, blue stars (e.g. O-, B-, and A-type main sequence stars), Wolf-Rayet stars, and Galactic foreground stars.

Across 100 classification runs the PRF classified 162746 sources with an average estimated accuracy of ~86 per cent, based on confusion matrices. We identified 4985 YSOs across the disc of M 33, applying a density-based clustering analysis to identify 68 star forming regions (SFRs) primarily in the galaxy's spiral arms. SFR counterparts to known HII regions were recovered with ~91 per cent of SFRs spatially coincident with giant molecular clouds identified in the literature.