DEGAS — Dense Extragalactic GBT+Argus Survey

Abstract

The goal of DEGAS is to map four dense molecular gas tracers — HCN(1-0), HCO⁺(1-0), ¹³CO(1-0), and C¹⁸O(1-0) — over the central 4 arcmin² of 36 nearby galaxies.

Resolved observations in the Milky Way and integrated measurements in nearby galaxies have shown that the presence of molecular gas, in particular dense molecular gas, is linked to the presence of star formation. This trend, however, has a large amount of scatter suggesting that additional physical parameters beyond the amount of dense gas play a role in setting this relationship. Disentangling these parameters requires resolved measurements of dense molecular gas in environments with a much wider range of conditions than found in the Milky Way.

A obvious population to do this experiment in is nearby (<20 Mpc) galaxies where one can obtain sensitive, relatively high resolution (<500 pc) observations. Such observations were extremely difficult with the previous generation of millimeter telescopes because the brightest dense molecular gas tracers (HCN and HCO⁺) are fainter than CO by a factor of 10-30.

DEGAS leverages the fast mapping speed, excellent surface brightness sensitivity, and good resolution made possible by the combination of the 100m Green Bank Telescope and Argus, a 16-pixel focal plane array, to map dense molecular gas in many nearby galaxies. When complete it will represent the largest extragalactic dense molecular gas survey to date.