The Outer Disks of Spiral Galaxies
Molecular gas, via its CO emisssion, is detectable far out in the Milky Way, M33, NGC 4414, and probably all spirals with extended HI. Metallicity is not a great problem for CO detection in regions with a weak radiation field, such as outer disks. The association with HI and star formation is very good but not perfect –giant molecular clouds can be found in zones with little HI. In the outer Galaxy, there is no sharp decrease in CO line intensity despite the lack of obvious heating sources for outer galaxy clouds.
KeywordsStar Formation Molecular Cloud Spiral Galaxy Magellanic Cloud Outer Disk
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