# Massive young stellar objects in the Local Group spiral galaxy M33 identified using machine learning

**Authors:** David A. Kinson, Joana M. Oliveira, Jacco Th. van Loon  
**arXiv:** [2209.10371](https://arxiv.org/abs/2209.10371)  
**Date:** 2022-09-21  
**Summary page:** https://www.summarizepaper.com/en/paper/2209.10371v1/

## Key points

- Study focused on supervised machine learning classification of stellar populations in the Local Group spiral galaxy M\,33 using Probabilistic Random Forest (PRF) methodology
- Classification system utilized near and far-IR features to categorize sources into nine target classes
- Successfully classified 162,746 sources with an average estimated accuracy of approximately 86%
- Identified 4985 young stellar objects (YSOs) and 68 star forming regions (SFRs) within M\,33
- Introduced a novel approach utilizing ratios of [H$\alpha$]$/$[24$\mu$m] and [250$\mu$m]$/$[500$\mu$m] to estimate relative evolutionary status of SFRs
- Estimated masses for YSOs ranging from 6 to 27 solar masses and calculated star formation rates between 0.63\,$-$\,$1.42$ M$_{\odot}$ yr$^{-1}$ across different regions of M\,33
- Provided insights into ongoing star formation processes within the galactic environment by comparing properties of YSOs and SFRs with known structures in M\,33 and other galaxies in the Local Group

## Summary

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In this study, we present a supervised machine learning classification of stellar populations in the Local Group spiral galaxy M\,33 using the Probabilistic Random Forest (PRF) methodology. Our classification system incorporates both near and far-IR features to categorize sources into nine target classes, including young stellar objects (YSOs), asymptotic giant branch stars, red giant branch and red super-giant stars, active galactic nuclei, blue stars, Wolf-Rayet stars, and Galactic foreground stars. Through 100 classification runs, we accurately classified a total of 162,746 sources with an average estimated accuracy of approximately 86\%. Our analysis identified 4985 YSOs across the disk of M\,33 and pinpointed 68 star forming regions (SFRs) primarily located within the galaxy's spiral arms. These SFRs were found to be spatially coincident with giant molecular clouds identified in existing literature. By leveraging photometric measurements and an established evolutionary sequence from NGC\,6822 as a benchmark, we introduced a novel approach utilizing ratios of [H$\alpha$]$/$[24$\mu$m] and [250$\mu$m]$/$[500$\mu$m] to estimate the relative evolutionary status of all M\,33 SFRs. We also estimated masses for each YSO ranging from 6 to 27 solar masses and calculated star formation rates based on direct YSO counts. Our results indicate a star formation rate of 0.63\,$-$\,$1.42$ M$_{\odot}$ yr$^{-1}$ across different regions of M\,33. Furthermore, by examining the properties of YSOs and SFRs within the context of the galaxy's structure and comparing them to known H ii regions and GMCs in M\,33 as well as other galaxies in the Local Group such as NGC 604 in LMC, we provide valuable insights into ongoing star formation processes within this dynamic galactic environment.