Molecular clouds in the outer galaxy

Details Molecular clouds in the outer galaxy Molecular clouds in the outer galaxy

Sep 1986

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1986phdt........10m&link_type=abstract

Ph. D. Thesis Rensselaer Polytechnic Inst., Troy, NY.

Astronomy and Astrophysics

Astronomy

4

Carbon Monoxide, Far Infrared Radiation, Line Spectra, Milky Way Galaxy, Molecular Clouds, Radio Emission, Star Formation, Astronomical Models, Computerized Simulation, Continuous Spectra, H Ii Regions, Infrared Astronomy, Radio Astronomy, Space Temperature

Scientific paper

Physical conditions and related star forming activities were investigated in molecular clouds in the outer galaxy. Thirty-five molecular clouds were mapped in the CO(J = 1-0) line at lambda = 2.6 mm. Ten of these were mapped in (13)CO(J = 1-0) and CO(J = 2-1) (lambda = 1.3 mm). Far infrared continuum emission from dust was detected in four of six clouds searched and radio continuum emission from HII regions was mapped in 15 of 17 observed clouds. On a large scale, the CO emission follows the HI warp and there appears to be an arm at R approx. 13 kpc, coincident with a feature in the HI surface density distribution. Studying individual clouds reveals the following results. (1) Linestrength (TR*) ratios of the (12)CO(J = 1-0) and (13)CO(J = 1-0) lines at and near the cloud peaks are typically between 3 and 6, indicating that the CO is optically thick. (2) Qualitative analyses of the CO(J = 1-0 and J = 2-1) line-strengths in the envelopes indicate low kinetic temperatures in the clouds. (3) Peak TR*'s are found to decrease somewhat with an increase in galactocentric distance, R, indicating that the peaks are beam diluted. (4) Most clouds lie between R = 11.5 kpc and R = 14 kpc. At larger R's few clouds were found; and they have drastically lower linestrengths, indicating that the CO at R greater than 14.5 kpc is either sparse or cold. (5) An average cloud is 40 pc in the longest dimension. (6) Most clouds have masses from 10(4). 10(5) solar mass (7) Continuum emission was detected in four of six clouds searched in the infrared and 15 of 17 clouds searched at 6 cm. Spectral types of embedded stars derived from the continuum data were between O7 and B3; most were B1 or B2.

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