GBT26A-451

Tracers of PAH formation at the edges of molecular clouds: source verification

Abstract

The first all-sky 3D map of the dust extinction curve at optical wavelengths has revealed evidence suggesting in situ growth of polycyclic aromatic hydrocarbons (PAHs) in multiple molecular clouds across the Milky Way. The map exhibits a surprising steepening rather than the expected flattening of extinction curves in multiple molecular clouds. A leading interpretation is that growth of polycyclic aromatic hydrocarbons enhances the 2175 ?? feature, contributing extinction at blue optical wavelengths significantly more than red wavelengths. In future cycles, we will propose a robust test of the hypothesis that the 2175 ?? feature is the major driver of extinction curve variation by searching for signals of PAHs with the GBT in regions displaying this steepening. Before investing non-trivial GBT observing hours, here we propose for short source-verification observations targeting cyanopolyyne molecules and c-C3H2, key tracers of PAH formation, in the cloud Perseus, Orion, Cepheus and a currently unnamed region. A positive detection would motivate deeper follow-up observations and offer valuable insights into the chemical evolution of the interstellar medium, as well as the origin of anomalous PAH signal observed in cosmic-dawn galaxies.

Investigators

Name	Institution
Xiangyu Zhang *	Max-Planck-Institut für Astronomie
Brett McGuire	National Radio Astronomy Observatory; Massachusetts Institute of Technology
Brandon Hensley	Princeton University
Gregory Green	Max-Planck-Institut für Astronomie

* indicates the PI