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2001ApJ...547..792D - Astrophys. J., 547, 792-813 (2001/February-1)
The Milky Way in molecular clouds: a new complete CO survey.
DAME T.M., HARTMANN D. and THADDEUS P.
Abstract (from CDS):
The composite maps provide detailed information on individual molecular clouds, suggest relationships between clouds and regions widely separated on the sky, and clearly display the main structural features of the molecular Galaxy. In addition, since the gas, dust, and Population I objects associated with molecular clouds contribute to the Galactic emission in every major wavelength band, the precise kinematic information provided by the present survey will form the foundation for many large-scale Galactic studies.
A map of molecular column density predicted from complete and unbiased far-infrared and 21 cm surveys of the Galaxy was used both to determine the completeness of the present survey and to extrapolate it to the entire sky at |b|<32°. The close agreement of the observed and predicted maps implies that only ∼2% of the total CO emission at |b|<32° lies outside our current sampling, mainly in the regions of Chamaeleon and the Gum Nebula. Taking into account this small amount of unobserved emission, the mean molecular column density decreases from ∼3x1020 cm–2 at |b|=5° to ∼0.1x1020 cm–2 at |b|=30°; this drop is ∼6 times steeper than would be expected from a plane-parallel layer, but is consistent with recent measurements of the mean molecular column density at higher latitudes.
The ratio of the predicted molecular column density map to the observed CO intensity map provides a calibration of the CO-to-H2 mass conversion factor X≡NH2/WCO. Out of the Galactic plane (|b|>5°), X shows little systematic variation with latitude from a mean value of (1.8±0.3)x1020 cm–2.K–1.km–1.s. Given the large sky area and large quantity of CO data analyzed, we conclude that this is the most reliable measurement to date of the mean X value in the solar neighborhood.
Abstract Copyright: ∼
Journal keyword(s): Galaxy: Structure - ISM: Clouds - ISM: Molecules - Radio Lines: ISM - Galaxy: Solar Neighborhood - Stars: Formation
Simbad objects: 69
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