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Organic Molecules at the Outer Reaches of the Galaxy: Observations of CH₃OH, c-C₃H₂, and CH₃CN Beyond 15 kpc

Presentation #326.05 in the session “Dust and Astrochemistry”.

Published onJun 18, 2021
Organic Molecules at the Outer Reaches of the Galaxy: Observations of CH₃OH, c-C₃H₂, and CH₃CN Beyond 15 kpc

The Galactic Habitable Zone (GHZ), the region with favorable conditions for the formation of life, is thought to extend to only up to 10 kpc from the Galactic Center. This conclusion was partly based on the supposed dearth of organic molecules in the outer Galaxy. In order to better ascertain the boundaries of the GHZ, several K components of the J=2-1 transition of methanol, a basic organic molecule, were searched for towards 20 molecular clouds in the Cygnus arms using the 12m telescope of the Arizona Radio Observatory (ARO) at 3mm in wavelength. These clouds are typically cold (Tk ~ 20K) and are a distance of 13-23.5 kpc from the Galactic Center. CH3OH was detected in all 20 clouds, identified by multiple K components, with typical fractional abundances, relative to H2, of f ~ 109. Searches have now been extended to c-C3H2 and CH3CN in these clouds, using their 2mm transitions. Thus far, several lines of the J=4-3 transition of c-C3H2 have been detected in a few clouds, as well as hyperfine components of the J=3/2-1/2 transition of NO. The detection of these organic molecules at the Galactic edge may imply that organic chemistry is still prevalent at the outer reaches of the galaxy, and the GHZ may extend much further from the Galactic Center than the current established boundary.


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