VERY LARGE ARRAY OBSERVATIONS OF AMMONIA IN INFRARED-DARK CLOUDS. I. COLUMN DENSITY AND TEMPERATURE STRUCTURE
- Department of Astronomy, University of Michigan, 830 Dennison Building, 500 Church Street, Ann Arbor, MI 48109 (United States)
- Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
We present Very Large Array observations of NH{sub 3} (1,1) and (2,2) in a sample of six infrared-dark clouds (IRDCs) with distances from 2 to 5 kpc. We find that ammonia serves as an excellent tracer of dense gas in IRDCs, showing no evidence of depletion, and the average abundance in these clouds is 8.1 x 10{sup -7}. Our sample consists of four IRDCs with 24 {mu}m embedded protostars and two that appear starless. We calculate the kinetic temperature of the gas in IRDCs and find no significant difference between starless and star-forming IRDCs. We find that the bulk of the gas is between 8 and 13 K, indicating that any embedded or nearby stars or clusters do not affect the gas temperature dramatically. Though IRDCs have temperatures and volume densities on par with local star formation regions of lower mass, they consist of much more mass which induces very high internal pressures. In order for IRDCs to survive as coherent structures, the internal pressure must be balanced by a confining pressure provided by the high concentration of molecular clouds in the spiral arm in which they reside. The high molecular concentration and pressure are roughly consistent with gas dynamics of a bar galaxy.
- OSTI ID:
- 21578231
- Journal Information:
- Astrophysical Journal, Vol. 736, Issue 2; Other Information: DOI: 10.1088/0004-637X/736/2/163; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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