Detailed observations of the M17 molecular cloud complex

Journal Article · Wed Dec 01 04:00:00 EST 1976 · Astrophys. J., Suppl. Ser.; (United States)

DOI:https://doi.org/10.1086/190409· OSTI ID:7330060

Lada, C J

Detailed molecular line observations of CO, CS, H/sub 2/CO, NH/sub 3/, and some of their isotopes toward the giant molecular cloud complex near M17 are presented and discussed. Extensive /sup 12/CO and /sup 13/CO observations are made of two separation clouds characterized by velocities of 20 and 23 km s/sup -1/. The cloud at 20 km s/sup -1/ is found to be approximately 15' x 30' (10 x 20 pc) in extent and to contain a mass in excess of 3 x 10/sup 4/ M/sub sun/. Within the 20 km s/sup -1/ cloud are three bright spots of /sup 12/CO emission, two of which are shown to be localized high-density fragments a few parsecs in size. Subsequent identification of infrared sources and H/sub 2/O maser sources within their boundaries is interpreted as an indication that star formation has recently taken place. Observations of millimeter-wave CO, CS, HCN, H/sub 2/CO, and SO and centimeter-wave NH/sub 3/ emission and H/sub 2/CO absorption are combined with model cloud calculations manner to determine the physical and chemical conditions in M17 SW, the largest of the CO bright spots. Integrated intensity ratios of /sup 13/CO to C/sup 18/O are found to be significantly the terrestrial value. Line widths of /sup 12/CO and /sup 13/CO are found to increase near M17 SW. It is found that the entire cloud cannot be in uniform spherical collapse of any form. Collapse, however, could be in progress in a small region around M17 SW, but lack of sufficient angular resolution prohibits direct observational tests of this possibility. It is concluded that line widths of approx.3 km s/sup -1/ must be maintained by some mechanism other than systematic collapse or expansion motions. Comparison of the molecular line observations with optical, infrared, and radio continuum data is made. The 20 km s/sup -/1 molecular cloud, the M17 H II region, and the star cluster NGC 6618 are apparently related in a geometrical evolutionary sequence. Cloud evolution seems to have proceeded from the outer edge of a proto-molecular cloud inward.

• Research Organization: Center for Astrophysics, Harvard College Observatory
• OSTI ID: 7330060
• Journal Information: Astrophys. J., Suppl. Ser.; (United States), Journal Name: Astrophys. J., Suppl. Ser.; (United States) Vol. 32:4; ISSN APJSA
• Country of Publication: United States
• Language: English

Related Subjects

640105* -- Astrophysics & Cosmology-- Galaxies
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ABUNDANCE
ALDEHYDES
AMMONIA
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CARBON SULFIDES
CHALCOGENIDES
CHEMICAL COMPOSITION
CHEMISTRY
COSMIC RADIO SOURCES
COSMOCHEMISTRY
ELECTROMAGNETIC RADIATION
ENERGY-LEVEL TRANSITIONS
FORMALDEHYDE
GRAVITATIONAL COLLAPSE
H2 REGIONS
HYDRIDES
HYDROCYANIC ACID
HYDROGEN COMPOUNDS
INORGANIC ACIDS
ISOTOPES
LINE WIDTHS
NEBULAE
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
RADIATIONS
RADIOWAVE RADIATION
STAR ACCRETION
STAR CLUSTERS
STAR EVOLUTION
SULFIDES
SULFUR COMPOUNDS
SULFUR OXIDES