Pillai, T. and Kauffmann, J. and Wyrowski, F. and Hatchell, J. and Gibb, A. G. and Thompson, M. A. (2011) Probing the initial conditions of high-mass star formation. II. Fragmentation, stability, and chemistry towards high-mass star-forming regions G29.96−0.02 and G35.20−1.74. Astronomy and Astrophysics, 530 . Art. No. A118. ISSN 0004-6361 http://resolver.caltech.edu/CaltechAUTHORS:20110613-085854844
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Most work on high-mass star formation has focused on observations of young massive stars in protoclusters. Very little is known about the preceding stage. Here, we present a new high-resolution study of pre-protocluster regions in tracers exclusively probing the coldest and dense gas (NH_2D). The two target regions G29.96−0.02 and G35.20−1.74 (W48) are drawn from the SCAMPS project, which searches for pre-protoclusters near known ultracompact Hii regions. We used our data to constrain the chemical, thermal, kinematic, and physical conditions (i.e., densities) in G29.96e and G35.20w. NH_3, NH_2D, HCO^+ , and continuum emission were mapped using the VLA, PdBI, and BIMA. In particular, NH_2D is a unique tracer of cold, precluster gas at high densities, while NH_3 traces both the cold and warm gas of modest-to-high densities. In G29.96e, Spitzer images reveal two massive filaments, one of them in extinction (infrared dark cloud). Dust and line observations reveal fragmentation into multiple massive cores strung along filamentary structures. Most of these are cold (<20 K), dense (>10^5 cm^(-3)) and highly deuterated ([NH_2D/NH_3] > 6%). In particular, we observe very low line widths in NH_2D (FWHM ≲ 1 km s^(-1)). These are very narrow lines that are unexpected towards a region forming massive stars. Only one core in the center of each filament appears to be forming massive stars (identified by the presence of masers and massive outflows); however, it appears that only a few such stars are currently forming (i.e., just a single Spitzer source per region). These multi-wavelength, high-resolution observations of high-mass pre-protocluster regions show that the target regions are characterized by (i) turbulent Jeans fragmentation of massive clumps into cores (from a Jeans analysis); (ii) cores and clumps that are “over-bound/subvirial”, i.e. turbulence is too weak to support them against collapse, meaning that (iii) some models of monolithic cloud collapse are quantitatively inconsistent with data; (iv) accretion from the core onto a massive star, which can (for observed core sizes and velocities) be sustained by accretion of envelope material onto the core, suggesting that (similar to competitive accretion scenarios) the mass reservoir for star formation is not necessarily limited to the natal core; (v) high deuteration ratios ([NH_2D/NH_3] > 6%), which make the above discoveries possible; (vi) and the destruction of NH_2D toward embedded stars.
|Additional Information:||© 2011 ESO. Received 7 October 2010. Accepted 31 March 2011. Published online: 23 May 2011. Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain). We thank an anonymous referee for a very thorough review which helped to significantly improve the paper. T.P. acknowledges support from the Combined Array for Research in Millimeter-wave Astronomy (CARMA), which is supported by the National Science Foundation through grant AST 05-40399. J.K. also thanks Di Li, his host at JPL, for making this research possible. This project was supported by an appointment of J.K. to the NASA Postdoctoral Program at the Jet Propulsion Laboratory, administered by Oak Ridge Associated Universities through a contract with NASA. J.K.s research was executed at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Air and Space Administration. This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA.|
|Subject Keywords:||astrochemistry; molecular data; turbulence; ISM: clouds; ISM: jets ond outflows; ISM: molecules|
|Official Citation:||Probing the initial conditions of high-mass star formation - II. Fragmentation, stability, and chemistry towards high-mass star-forming regions G29.96−0.02 and G35.20−1.74 A118 T. Pillai, J. Kauffmann, F. Wyrowski, J. Hatchell, A. G. Gibb and M. A. Thompson Published online: 23 May 2011 DOI: 10.1051/0004-6361/201015899|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||13 Jun 2011 17:03|
|Last Modified:||26 Dec 2012 13:18|
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