PHYSICAL PROPERTIES AND GALACTIC DISTRIBUTION OF MOLECULAR CLOUDS IDENTIFIED IN THE GALACTIC RING SURVEY

Journal Article · Mon Nov 01 04:00:00 EDT 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/723/1/492· OSTI ID:21467180

Roman-Duval, Julia; Jackson, James M ^[1]; Heyer, Mark ^[2]; Rathborne, Jill ^[3]; Simon, Robert ^[4]

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1. Institute for Astrophysical Research at Boston University, 725 Commonwealth Avenue, Boston, MA 02215 (United States)
2. Department of Astronomy, University of Massachusetts, Amherst, MA 01003-9305 (United States)
3. Departamento de Astronomia, Universidad de Chile, Santiago (Chile)
4. Physikalisches Instituet, Universitaet zu Koeln, 50937 Koeln (Germany)

We derive the physical properties of 580 molecular clouds based on their {sup 12}CO and {sup 13}CO line emission detected in the University of Massachusetts-Stony Brook (UMSB) and Galactic Ring surveys. We provide a range of values of the physical properties of molecular clouds, and find a power-law correlation between their radii and masses, suggesting that the fractal dimension of the interstellar medium is around 2.36. This relation, M = (228 {+-} 18) R {sup 2.36{+-}0.04}, allows us to derive masses for an additional 170 Galactic Ring Survey (GRS) molecular clouds not covered by the UMSB survey. We derive the Galactic surface mass density of molecular gas and examine its spatial variations throughout the Galaxy. We find that the azimuthally averaged Galactic surface density of molecular gas peaks between Galactocentric radii of 4 and 5 kpc. Although the Perseus arm is not detected in molecular gas, the Galactic surface density of molecular gas is enhanced along the positions of the Scutum-Crux and Sagittarius arms. This may indicate that molecular clouds form in spiral arms and are disrupted in the inter-arm space. Finally, we find that the CO excitation temperature of molecular clouds decreases away from the Galactic center, suggesting a possible decline in the star formation rate with Galactocentric radius. There is a marginally significant enhancement in the CO excitation temperature of molecular clouds at a Galactocentric radius of about 6 kpc, which in the longitude range of the GRS corresponds to the Sagittarius arm. This temperature increase could be associated with massive star formation in the Sagittarius spiral arm.

• OSTI ID: 21467180
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 723; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CHALCOGENIDES
EMISSION
FRACTALS
GALAXIES
OXIDES
OXYGEN COMPOUNDS
STARS