Massive Young Stellar Objects in the G333 Giant Molecular Cloud

Details Massive Young Stellar Objects in the G333 Giant Molecular Cloud Massive Young Stellar Objects in the G333 Giant Molecular Cloud

Jan 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21541435s&link_type=abstract

American Astronomical Society, AAS Meeting #215, #414.35; Bulletin of the American Astronomical Society, Vol. 42, p.259

Astronomy and Astrophysics

Astronomy

Scientific paper

The G333 giant molecular cloud (GMC) contains a few star clusters and H II regions (e.g., G333.6-0.2) plus a number of condensations currently forming stars. The star clusters all lie along the major axis of the cloud. Although the usual expectation is that star formation occurs in the centers of GMCs where the density is highest, there clearly are additional sites at the extremities of the cloud. We have identified a number of such sites from Spitzer IRAC and MIPS Legacy programs GLIMPSE and MIPSGAL images. These sites contain objects with the appearance of young stellar objects (YSOs) - all of them are very red, with spectral energy distributions peaking at wavelengths longer than 24 micron or even 70 micron. Some also have extended emission at 4.5 micron (IRAC band 2) that is ascribed to outflows. We have mapped a dozen of these sources with the Spitzer Infrared Spectrograph in the Short-Low, Short-High, and Long-High modules (5-36 micron). All spectral maps show the characteristics of H II regions: ionized forbidden lines and polycyclic aromatic hydrocarbon emission features. For four of the twelve sources, these lines are concentrated to the centers of the maps, from which we infer that YSOs can be the source of ionizing photons. For the sources with 4.5 micron emission, the H II region features have a minimum at the map center, probably due to very high extinction in the YSO envelope. This envelope extinction is characterized by deep silicate absorption features and by absorption by ices at 6.0, 6.8, and 15 micron. It has been suggested that the extended emission at 4.5 micron is due to emission by shocked H2 S(9) lines. This explanation is excluded by our lack of detection or very weak measured H2 S(3), S(5), and S(7) lines.

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