Complex organic molecules in the Galactic Centre: the N-bearing family

TL;DR

This study uncovers a rich variety of nitrogen-bearing complex organic molecules in the Galactic Centre's quiescent cloud, revealing unique chemistry driven by shocks and cosmic rays, distinct from star-forming regions.

Contribution

First unbiased spectral survey of N-bearing molecules in a Galactic Centre quiescent cloud, identifying 17 species including 8 complex organics, and analyzing their chemical environment.

Findings

Detected 17 N-bearing species, 8 of which are complex organic molecules.

Chemistry likely dominated by low-velocity shocks and cosmic rays.

N-bearing molecules show more efficient hydrogenation than in hot cores.

Abstract

We present an unbiased spectral line survey toward the Galactic Centre (GC) quiescent giant molecular cloud (QGMC), G+0.693 using the GBT and IRAM 30$\,$ telescopes. Our study highlights an extremely rich organic inventory of abundant amounts of nitrogen (N)-bearing species in a source without signatures of star formation. We report the detection of 17 N-bearing species in this source, of which 8 are complex organic molecules (COMs). A comparison of the derived abundances relative to H$_2$ is made across various galactic and extragalactic environments. We conclude that the unique chemistry in this source is likely to be dominated by low-velocity shocks with X-rays/cosmic rays also playing an important role in the chemistry. Like previous findings obtained for O-bearing molecules, our results for N-bearing species suggest a more efficient hydrogenation of these species on dust grains in G+0.693 than in hot cores in the Galactic disk, as a consequence of the low dust temperatures coupled with energetic processing by X-ray/cosmic ray radiation in the GC.