The search for prebiotic organic molecules in the outer Galaxy

Abstract

This study was conducted to determine the distribution and abundance of two key prebiotic organic molecules, H2CO and HCN, in outer Galaxy giant molecular clouds. Both H2CO and HCN most likely played important roles in the formation of amino acids on the early Earth. By determining the distribution of these molecules in the outer Galaxy, the current definition of a Galactic Habitable Zone, the region where conditions are conducive to the formation of life, may be better constrained. We looked for H2CO in a sample of 69 molecular clouds at distances ranging from 12 to 23.5 kpc from the Galactic Center, and in a subset of these clouds, 46 of 69, we looked for HCN. The H2CO (212-111) spectral line at 140.8 GHz was detected in 65% of the cloud,s and the HCN (J=1-0) spectral line at 88.6 GHz was detected in 67% of the clouds. The H2CO (101-111) spectral line at 4.83 GHz and the H2CO (312 -211) spectral line at 225.6 GHz were also detected towards a subset of the clouds. A multi-transition study was conducted for H2CO using a statistical equilibrium code in the large velocity gradient (LVG) approximation to better estimate abundances of H2CO. We conclude that H2CO and HCN are found readily in the outer Galaxy, and that the widespread distribution of these molecules may indicate that the outer Galaxy could possibly be hospitable to the formation of life.