The Central 300 pc of the Galaxy Probed by Infrared Spectra of H$_3^+$ and CO: III. Locations of Sgr B2 and Star $\iota$

TL;DR

This study estimates the three-dimensional locations of Star $f$ and Sgr B2 within the Galactic Center's Central Molecular Zone using infrared spectral line velocities, revealing Sgr B2 is farther behind Sgr A$^\ast$ than previously thought.

Contribution

It introduces a method to determine the physical depths of objects in the CMZ using velocity profiles of infrared absorption lines, challenging prior models of Sgr B2's position.

Findings

Sgr B2 is approximately 90 pc behind Sgr A$^\ast$.

Sgr B2 is located toward the rear of the CMZ, contrary to earlier models.

The method links gas velocity profiles to spatial positioning within the CMZ.

Abstract

Using a simple relation between the radial expansion velocity of diffuse gas in the Central Molecular Zone (CMZ) of the Galaxy and its distance from Sgr A$^\ast$ we estimate the physical depths within the CMZ of Star $\iota$ (2MASS $J$17470898-2829561) and two Sgr B2 far-infrared continuum sources with respect to the location of Sgr A$^\ast$. To do this we use velocity profiles of mid-infrared absorption lines of H$_3^+$ and of far-infrared absorption lines of H$_2$O$^+$, OH$^+$, and $^{13}$CH$^+$. The distances to Star $\iota$ and to the Sgr B2 sources are found to be $\sim$90 pc greater than the distance to Sgr A$^\ast$. Our conclusion that Sgr B2 lies toward the rear of the CMZ is contrary to many previous models in which it has been placed shallower than Sgr A$^\ast$.