Molecular gas in the immediate vicinity of Sgr A* seen with ALMA

TL;DR

This study presents high-resolution ALMA observations revealing detailed molecular gas structures near Sgr A*, including the first resolved images of various molecules, indicating complex excitation and chemical processes in the Galactic center's immediate vicinity.

Contribution

First high-resolution images of multiple sub-mm molecules near Sgr A*, revealing molecular cloud dynamics and chemical conditions within the central parsec of the Galaxy.

Findings

The central association has higher CS/X ratios than the circumnuclear disk.

The central association is likely closer to Sgr A* and may be an infalling dense clump.

Regions identified for future studies on star formation and extreme chemistry.

Abstract

We report serendipitous detections of line emission with ALMA in band 3, 6, and 7 in the central parsec of the Galactic center at an up to now highest resolution (<0.7''). Among the highlights are the very first and highly resolved images of sub-mm molecular emission of CS, H13CO+, HC3N, SiO, SO, C2H, and CH3OH in the immediate vicinity (~1'' in projection) of Sgr A* and in the circumnuclear disk (CND). The central association (CA) of molecular clouds shows three times higher CS/X (X: any other observed molecule) luminosity ratios than the CND suggesting a combination of higher excitation - by a temperature gradient and/or IR-pumping - and abundance enhancement due to UV- and/or X-ray emission. We conclude that the CA is closer to the center than the CND is and could be an infalling clump consisting of denser cloud cores embedded in diffuse gas. Moreover, we identified further regions in and outside the CND that are ideally suited for future studies in the scope of hot/cold core and extreme PDR/XDR chemistry and consequent star formation in the central few parsecs.