The Red MSX Source Survey: the Massive Young Stellar Population of our Galaxy (1308.0134v2)

Abstract: We present the Red MSX Source (RMS) Survey, the largest statistically selected catalog of young massive protostars and HII regions to date. We outline the construction of the catalog using mid and near infrared color selection, as well as the detailed follow up work at other wavelengths, and at higher spatial resolution in the infrared. We show that within the adopted selection bounds we are more than 90% complete for the massive protostellar population, with a positional accuracy of the exciting source of better than 2 arcseconds. We briefly summarize some of the results that can be obtained from studying the properties of the objects in the catalog as a whole, and find evidence that the most massive stars form: (i) preferentially nearer the Galactic centre than the anti-centre; (ii) in the most heavily reddened environments, suggestive of high accretion rates; and (iii) from the most massive cloud cores.

The Red MSX Source Survey: Insights into the Massive Young Stellar Population of Our Galaxy

The paper "The Red MSX Source Survey: the Massive Young Stellar Population of our Galaxy" by S.L. Lumsden et al. presents an extensive paper of young massive protostars and HII regions in the Milky Way. This survey, referred to as the Red MSX Source (RMS) Survey, is the largest statistically significant catalog of its kind, aimed at enhancing our understanding of massive star formation processes.

Survey Overview and Methodology

The RMS Survey was constructed using mid and near-infrared data from the MSX satellite mission and the 2MASS survey to identify candidates for young massive stars through color selection. The authors report a high completeness of over 90%, with a positional accuracy better than 2 arcseconds for the exciting sources. Follow-up observations at other wavelengths, including radio and submillimeter data, allowed for a comprehensive classification of the objects, offering insights into their nature, environmental properties, and evolutionary stages.

Key Findings

1. Spatial Distribution: A notable finding from the catalog analysis is the spatial distribution of massive stars. The data suggest that the most massive stars preferentially form closer to the Galactic center, in regions with high dust extinction, indicating high accretion rates and formation from the most massive cloud cores.
2. Massive Star Formation Models: The survey's results contribute significantly to the discourse on massive star formation. The authors discuss the implications of their findings on current theoretical models, including monolithic collapse and competitive accretion. The virialized motions observed in the massive cores suggest a preference for monolithic collapse models but do not exclude competitive accretion, particularly at an early stage.
3. Radio Emission and Early Evolution: The paper also highlights the unexpected radio luminosity of young B-stars, suggesting an excess of Lyman continuum photons compared to predictions from models of main sequence stars. This finding indicates that young intermediate-mass stars might not conform completely to existing models, hinting at complexities in their atmospheric structures or external heating mechanisms.
4. Galactocentric Variation: The radial distribution of the surveyed sources indicates a deficiency of massive stars forming beyond a Galactocentric radius of 8.5 kpc. This observational result supports theories regarding the impact of spiral density waves and triggering processes prevalent in the inner Galaxy regions.

Future Directions

The RMS catalog stands as a pivotal resource for ongoing and future research into the early stages of massive star formation. The research community can leverage this catalog to explore processes in massive star clusters and to cross-correlate with other datasets such as the methanol multibeam survey and ATLASGAL. Future work could also explore the role of magnetic fields and more sophisticated radiative transfer models to comprehend the complexities observed in massive protostellar environments.

In summary, the RMS Survey provides an unprecedentedly detailed view of young massive stellar populations in our galaxy. It serves as a foundation for distinguishing between competing theories of massive star formation and offers rich possibilities for future theoretical and observational studies in stellar astrophysics.