Large-Scale Grain Mantle Disruption in the Galactic Center

We present observations of C2H5OH toward molecular clouds in Sgr A and Sgr B2 and associated with thermal and nonthermal features in the Galactic center (GC). C2H5OH emission in Sgr A and Sgr B2 is widespread but not uniform. C2H5OH emission is much weaker, or it is not detected in some molecular clouds in both complexes, in particular those with radial velocities between 70 and 120 km s-1. While most of the clouds associated with the thermal features do not show C2H5OH emission, that associated with the nonthermal radio arc shows emission. The fractional abundance of C2H5OH in most of the clouds with radial velocities between 0 and 70 km s-1 in Sgr A and Sgr B2 is relatively high, of a few times 10-8. The C2H5OH abundance decreases by more than a factor of 10 (≲10-9) in the clouds associated with the thermal features. The large abundance of C2H5OH in the gas phase indicates that C2H5OH has formed in grains and released to gas phase by shocks in the last ~105 yr. The implications of this finding in the origin of the shocks in the GC is briefly discussed.