Molecular clouds and galactic spiral structure

Thesis/Dissertation · Sat Jan 01 04:00:00 EST 1983

OSTI ID:6581995

Dame, T M

Galactic CO line emission at 115 GHz has been surveyed in the region 12/sup 0/ less than or equal to l less than or equal to 60/sup 0/ and -1/sup 0/ less than or equal to b less than or equal to 1/sup 0/ in order to study the distribution of molecular clouds in the inner galaxy; an inner strip 0/sup 0/.5 wide has been sampled every beamwidth (0/sup 0/.125), the rest every two beamwidths. Comparison of the survey with similar HI data reveals a detailed correlation with the most intense 21-cm features, implying that the CO and HI trace the same galactic features and have the same large-scale kinematics. To each of the classical 21-cm (HI) spiral arms of the inner galaxy there corresponds a CO molecular arm which is generally more clearly defined and of higher contrast. A simple model is developed in which all of the CO emission from the inner galaxy arises from spiral arms. The modeling results suggest that molecular clouds are essentially transient objects, existing for 15 to 40 million years after their formation in a spiral arm, and are largely confined to spiral features about 300 pc wide. A variety of methods are employed to estimate distances and masses for the largest clouds detected by the inner-galaxy survey and a catalogue is compiled. The catalogued clouds, the largest of which have masses of several 10/sup 6/ M/sub sunmass/ and linear dimensions in excess of 100 pc, are found to be excellent spiral-arm tracers. One of the nearest of the clouds, that associated with the supernova remnant W44, is fully mapped in both CO and /sup 13/CO and is discussed in detail.

• Research Organization: Columbia Univ., New York (USA)
• OSTI ID: 6581995
• Country of Publication: United States
• Language: English

Related Subjects

640105* -- Astrophysics & Cosmology-- Galaxies
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CATALOGS
CHALCOGENIDES
CONFIGURATION
COSMIC DUST
COSMIC GASES
DATA
DISTRIBUTION
DOCUMENT TYPES
DUSTS
ELEMENTS
EMISSION SPECTRA
EXPERIMENTAL DATA
FLUIDS
GALAXIES
GASES
HYDROGEN
INFORMATION
MILKY WAY
NONMETALS
NUMERICAL DATA
OXIDES
OXYGEN COMPOUNDS
SPATIAL DISTRIBUTION
SPECTRA
SPIRAL CONFIGURATION