Maser Activity of Organic Molecules toward Sgr B2(N)

TL;DR

This study maps and models maser emissions from organic molecules in Sgr B2(N), revealing spatial relationships and excitation mechanisms using interferometry and non-LTE radiative transfer analysis.

Contribution

First interferometric maps of CH$_2$NH and CH$_3$OH masers in Sgr B2(N), along with a new modeling tool for analyzing molecular maser signals.

Findings

Detected the first 84 GHz CH$_3$OH Class I maser in Sgr B2(N)

Mapped the CH$_2$NH maser at 5.29 GHz and found spatial correlation with CH$_3$OH masers

Supported collisional pumping mechanisms for these masers

Abstract

At centimeter wavelengths, single-dish observations have suggested that the Sagittarius (Sgr) B2 molecular cloud at the Galactic Center hosts weak maser emission from several organic molecules, including CH$_2$NH, HNCNH, and HCOOCH$_3$. However, the lack of spatial distribution information of these new maser species has prevented us from assessing the excitation conditions of the maser emission as well as their pumping mechanisms. Here, we present a mapping study toward Sgr B2 North (N) to locate the region where the complex maser emission originates. We report the first detection of the Class I methanol (CH$_3$OH) maser at 84 GHz and the first interferometric map of the methanimine (CH$_2$NH) maser at 5.29 GHz toward this region. In addition, we present a tool for modeling and fitting the unsaturated molecular maser signals with non-LTE radiative transfer models and Bayesian analysis using the Markov-Chain Monte Carlo approach. These enable us to quantitatively assess the observed spectral profiles. The results suggest a two-chain-clump model for explaining the intense CH$_3$OH Class I maser emission toward a region with low continuum background radiation. By comparing the spatial origin and extent of maser emission from several molecular species, we find that the 5.29 GHz CH$_2$NH maser has a close spatial relationship with the 84 GHz CH$_3$OH Class I masers. This relationship serves as observational evidence to suggest a similar collisional pumping mechanism for these maser transitions.