THE GALACTIC CENSUS OF HIGH- AND MEDIUM-MASS PROTOSTARS. I. CATALOGS AND FIRST RESULTS FROM MOPRA HCO{sup +} MAPS
- Astronomy Department, University of Florida, Gainesville, FL 32611 (United States)
- Center for Astronomy, Ibaraki University, 2-1-1 Bunkyo, Mito, Ibaraki 310-8512 (Japan)
- Department of Astrophysics, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602 (Japan)
The Census of High- and Medium-mass Protostars (CHaMP) is the first large-scale, unbiased, uniform mapping survey at sub-parsec-scale resolution of 90 GHz line emission from massive molecular clumps in the Milky Way. We present the first Mopra (ATNF) maps of the CHaMP survey region (300{sup 0} > l > 280{sup 0}) in the HCO{sup +} J = 1 {yields} 0 line, which is usually thought to trace gas at densities up to 10{sup 11} m{sup -3}. In this paper, we introduce the survey and its strategy, describe the observational and data reduction procedures, and give a complete catalog of moment maps of the HCO{sup +} J = 1{yields}0 emission from the ensemble of 303 massive molecular clumps. From these maps we also derive the physical parameters of the clumps, using standard molecular spectral-line analysis techniques. This analysis yields the following range of properties: integrated line intensity 1-30 K km s{sup -1}, peak line brightness 1-7 K, linewidth 1-10 km s{sup -1}, integrated line luminosity 0.5-200 K km s{sup -1} pc{sup 2}, FWHM size 0.2-2.5 pc, mean projected axial ratio 2, optical depth 0.08-2, total surface density 30-3000 M{sub sun} pc{sup -2}, number density (0.2-30) x 10{sup 9} m{sup -3}, mass 15-8000 M{sub sun}, virial parameter 1-55, and total gas pressure 0.3-700 pPa. We find that the CHaMP clumps do not obey a Larson-type size-linewidth relation. Among the clumps, there exists a large population of subthermally excited, weakly emitting (but easily detectable) dense molecular clumps, confirming the prediction of Narayanan et al. These weakly emitting clumps comprise 95% of all massive clumps by number, and 87% of the molecular mass, in this portion of the Galaxy; their properties are distinct from the brighter massive star-forming regions that are more typically studied. If the clumps evolve by slow contraction, the 95% of fainter clumps may represent a long-lived stage of pressure-confined, gravitationally stable massive clump evolution, while the CHaMP clump population may not engage in vigorous massive star formation until the last 5% of their lifetimes. The brighter sources are smaller, denser, more highly pressurized, and closer to gravitational instability than the less bright sources. Our data suggest that massive clumps approach critical Bonnor-Ebert-like states at constant density, while others' suggest that lower-mass clumps reach such states at constant pressure. Evidence of global gravitational collapse of massive clumps is rare, suggesting that this phase lasts <1% of the clumps' lifetime.
- OSTI ID:
- 21560329
- Journal Information:
- Astrophysical Journal, Supplement Series, Vol. 196, Issue 1; Other Information: DOI: 10.1088/0067-0049/196/1/12; ISSN 0067-0049
- Country of Publication:
- United States
- Language:
- English
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