An ATCA Survey of Sagittarius~B2 at 7~mm: Chemical Complexity Meets Broadband Interferometry

TL;DR

This survey of Sagittarius B2(N) at 7 mm using ATCA provides extensive spectral line data, automated analysis scripts, and insights into the chemical complexity and physical conditions of the region, including the first detection of formamide in a translucent cloud.

Contribution

The paper introduces a broadband spectral survey with automated line fitting, revealing detailed molecular and recombination line data, and provides new insights into the chemical and physical environment of Sagittarius B2(N).

Findings

Detected ~500 spectral lines, including 53 molecular species.

Revealed highly variable molecular abundances and excitation conditions.

First detection of formamide in a translucent Galactic cloud.

Abstract

We present a 30 - 50 GHz survey of Sagittarius B2(N) conducted with the Australia Telescope Compact Array (ATCA) with 5 - 10 arcsec resolution. This work releases the survey data and demonstrates the utility of scripts that perform automated spectral line fitting on broadband line data. We describe the line-fitting procedure, evaluate the performance of the method, and provide access to all data and scripts. The scripts are used to characterize the spectra at the positions of three HII regions, each with recombination line emission and molecular line absorption. Towards the most line-dense of the three regions characterised in this work, we detect ~500 spectral line components of which ~90 per cent are confidently assigned to H and He recombination lines and to 53 molecular species and their isotopologues. The data reveal extremely subthermally excited molecular gas absorbing against the continuum background at two primary velocity components. Based on the line radiation over the full spectra, the molecular abundances and line excitation in the absorbing components appear to vary substantially towards the different positions, possibly indicating that the two gas clouds are located proximate to the star forming cores instead of within the envelope of Sgr B2. Furthermore, the spatial distributions of species including CS, OCS, SiO, and HNCO indicate that the absorbing gas components likely have high UV-flux. Finally, the data contain line-of-sight absorption by $\sim$15 molecules observed in translucent gas in the Galactic Center, bar, and intervening spiral arm clouds, revealing the complex chemistry and clumpy structure of this gas. Formamide (NH$_2$CHO) is detected for the first time in a translucent cloud.