Multiwavelength Observations of Massive Stellar Cluster Candidates in the Galaxy

Abstract

The Galaxy appears to be richer in young, massive stellar clusters than previously known, due to advances in infrared surveys which have uncovered deeply embedded regions of star formation. Young, massive clusters can significantly impact the surrounding interstellar medium (ISM) and hence radio observations can also be an important tracer of their activity. Several hundred cluster candidates are now known by examining survey data. Here we report on multiwavelength observations of six of these candidates in the Galaxy. We carried out 4.9 and 8.5 GHz VLA observations of the radio emission associated with these clusters to obtain the physical characteristics of the surrounding gas, including the Lyman continuum photon flux and ionized gas mass. Spitzer Infrared Array Camera observations were also made of these regions, and provide details on the stellar population as well as the dust continuum and polycyclic aromatic hydrocarbon emission. When compared to the known young, massive clusters in the Galaxy, the six cluster candidates have less powerful Lyman ionizing fluxes and ionize less of the H II mass in the surrounding ISM. Therefore, these cluster candidates appear to be more consistent with intermediate-mass clusters (10^3-10^4 Msun).

39 pages, 20 figures. Accepted in the Astronomical Journal; to be published Fall 2012

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• The Massive Star-Forming Regions Omnibus X-Ray Catalog, Second Installment
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• Mass function of a young cluster in a low-metallicity environment. Sh 2-209
• The Youngest Globular Clusters
• Effects of physical conditions on the stellar initial mass function: The low-metallicity star-forming region Sh 2-209
• Spitzer Mid-infrared Study of Sh 2-208: Evolution of Protoplanetary Disks in Low-metallicity Environments
• Detections of massive stars in the cluster MCM2005b77, in the star-forming regions GRS G331.34$-$00.36 (S62) and GRS G337.92$-$00.48 (S36)
• Fragmented atomic shell around S187 HII region and its interaction with molecular and ionized gas