Computer Science
Scientific paper
Sep 1986
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1986phdt........13g&link_type=abstract
Thesis (PH.D.)--COLUMBIA UNIVERSITY, 1986.Source: Dissertation Abstracts International, Volume: 47-07, Section: B, page: 2959.
Computer Science
Galactic Structure, Co-Surveys, Star Formation
Scientific paper
Results from the first large-scale survey in the CO(J = 1 (--->) 0) line of the Vela-Carina-Centaurus region of the Southern Milky Way are reported. The observations, were spaced every beamwidth (0.125(DEGREES)) in the range 270(DEGREES) (LESSTHEQ) l (LESSTHEQ) 300(DEGREES) and -1(DEGREES) (LESSTHEQ) b (LESSTHEQ) 1(DEGREES), with latitude exten- sions to cover all Carina arm (l > 280(DEGREES)) emission beyond (VBAR)b(VBAR) = 1(DEGREES). In a concurrent survey every half-degree in latitude and longitude was sampled in the range 270(DEGREES) (LESSTHEQ) l (LESSTHEQ) 300(DEGREES) and -5(DEGREES) (LESSTHEQ) b (LESSTHEQ) 5(DEGREES) at a spatial resolution of 0.5(DEGREES). Both surveys had a spectral coverage of 330 km s('-1) with a resolution of 1.3 km s('-1). The Carina arm dominates the data. Its abrupt tangent at l (DBLTURN) 280(DEGREES) and characteristic loop in the l,v diagram are unmistakable evi- dence for CO spiral structure. When the emission is integrated over velocity and latitude, the height of the step seen in the tangent direc- tion suggests that the arm-interarm contrast is at least 13 to 1. Spatial maps of the arm exhibit a projected narrowing in latitude of the CO layer with increasing kinematic distance. Comparison of the CO and H I data shows close agreement between these two species in a seg - ment of the arm lying outside the solar circle (R(,o) = 10 kpc); within R(,o) the arm is more difficult to trace in H I than in CO. The distribution of the molecular layer about the galactic plane in the outer Galaxy is determined based on the assumption of axial symmetry with respect to the galactic center. Between R = 10.5 and 12.5 kpc, the average CO midplane dips from z = -48 to -167 pc below the b = 0(DEGREES) plane, following a similar well-known warping of the H I layer. In the same range of radii the half -thickness of the CO layer increases from 112 to 182 pc. Between l = 270(DEGREES) and 300(DEGREES), 27 molecular clouds are identified and cataloged along with heliocentric distances and masses. An additional 16 clouds beyond 300(DEGREES) are cataloged from an adjoining CO survey. The most massive ((GREATERTHEQ)10('5)M(,o)) of these clouds trace the Carina arm over 23 kpc in the plane of the Galaxy. The average mass for the Carina arm clouds is 1.4 x 10('6)M(,o), and the average intercloud spacing along the arm is 700 pc. Good agreement between the opti - cal and molecular pictures of the arm over 10 kpc reinforces the importance of giant molecular clouds as spiral tracers. One cloud is studied in detail. Comparison of the distribution of the Carina arm clouds with similarly massive molecular clouds in the first and second quadrants strongly suggests that the Carina and Sagittarius arms form a single spiral arm (TURN)40 kpc long wrapping two-thirds of the way around the Galaxy. (Abstract shortened with permission of author.).
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