Two New and Remarkable Sightlines through the Galactic Center's Molecular Gas

TL;DR

This study identifies two new sightlines through the Galactic Center's molecular gas, revealing complex absorption features and expanding our understanding of the gas distribution and dynamics in this region.

Contribution

The paper reports the discovery of two new infrared sightlines through the Galactic Center, expanding the range of observable gas and providing new insights into its structure and motion.

Findings

Spectra show multiple absorption components over 200 km/s

Largest equivalent width observed in interstellar H3+ line

First near-infrared view into the Sgr B star-forming region

Abstract

Until now the known sources in the Galactic center with sufficiently smooth spectra and of sufficient brightness to be suitable for high resolution infrared absorption spectroscopy of interstellar gas occupied a narrow range of longitudes, from the central cluster of hot stars to approximately 30 pc east of the center. In order to more fully characterize the gas within the r ~ 180 pc central molecular zone it is necessary to find additional such sources that cover a much wider longitudinal range. We are in the process of identifying luminous dust-embedded objects suitable for spectroscopy within 1.2 deg in longitude and 0.1 deg in latitude of Sgr A* using the Spitzer GLIMPSE and the 2MASS catalogues. Here we present spectra of H3+ and CO towards two such objects, one located 140 pc west of Sgr A*, and the other located on a line of sight to the Sgr B molecular cloud complex 85 pc to the east of Sgr A*. The sightline to the west passes through two dense clouds of unusually high negative velocities and also appears to sample a portion of the expanding molecular ring. The spectra toward Sgr B reveal at least ten absorption components covering over 200 km/s and by far the largest equivalent width ever observed in an interstellar H3+line; they appear to provide the first near-infrared view into that hotbed of star formation.