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

Content Provider	Scilit
Author	Roman-Duval, Julia Jackson, James M. Heyer, Mark Rathborne, Jill Simon, Robert
Copyright Year	2010
Description	Journal: The Astrophysical Journal We derive the physical properties of 580 molecular clouds based on their$ ^{12}$CO and$ ^{13}$CO line emission detected in the University of Massachusetts-Stony Brook (UMSB) and Galactic Ring surveys. We provide a range of values of the physical properties of molecular clouds, and find a power-law correlation between their radii and masses, suggesting that the fractal dimension of the interstellar medium is around 2.36. This relation, M = (228 ± 18) R$ ^{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.
Related Links	http://arxiv.org/pdf/1010.2798 http://iopscience.iop.org/article/10.1088/0004-637X/723/1/492/pdf
Ending Page	507
Page Count	16
Starting Page	492
ISSN	0004637X
DOI	10.1088/0004-637x/723/1/492
Journal	The Astrophysical Journal
Issue Number	1
Volume Number	723
Language	English
Publisher	IOP Publishing
Publisher Date	2010-10-12
Access Restriction	Open
Subject Keyword	Journal: The Astrophysical Journal Astronomy and Astrophysics Molecular Clouds Spiral Arm Sagittarius Arm
Content Type	Text
Resource Type	Article
Subject	Astronomy and Astrophysics Space and Planetary Science