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Distribution and motion of CO in M31

Published online by Cambridge University Press:  04 August 2017

Antony A. Stark
Antony A. Stark*
Affiliation:
Bell Laboratories, Holmdel, NJ 07733 USA

Abstract

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M31 is among the few galaxies whose solid angle is more than 100 times the beam area of currently operational millimeter-wave telescopes. Roughly 10% of its area has been mapped in the J=1→0 line of CO with the 7-m telescope at Bell Laboratories. The data lie on the major and minor axes and in a filled 20′ by 15′ field. The average CO emissivity is less than 1/5 that of the Milky Way Galaxy, and the inferred H2 column densities are less than 10% of the HI column densities at the same positions. Thus M31 has a predominantly atomic interstellar medium, whereas our Galaxy seems to have a predominantly molecular interstellar medium. The molecular emission is strongly concentrated in spiral-arm segments, with greater than 25:1 contrast between arm and interarm regions. Overall, the CO emission is well correlated with the HI emission, but shows greater concentration to the spiral arms. There is no evidence for a spatial separation of the HI and CO arms to within our resolution (~1′): all the spiral-arm tracers are spatially coincident. Almost all the gas on the minor axis exhibits non-circular velocities of about 20 km s-1. There are systematic streaming motions as large as 80 km s-1 associated with spiral arms.

Type
PART II: COMPOSITION, STRUCTURE AND KINEMATICS
Information
Symposium - International Astronomical Union , Volume 106: The Milky Way Galaxy , 1985 , pp. 445 - 450
Copyright
Copyright © Reidel 1985 

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