A High-Resolution Survey of HI Absorption toward the Central 200 pc of the Galactic Center

TL;DR

This high-resolution HI absorption survey of the Galactic Center's central 200 pc reveals detailed atomic gas distribution and its relation to ionized and molecular components, providing insights into the interstellar medium structure.

Contribution

First high-resolution HI absorption data for the central 250 pc of the Galaxy, enabling detailed comparison with ionized and molecular gas in key regions.

Findings

Atomic gas closely correlates with ionized and molecular gas in key regions.

HI absorption by the 3-kpc arm indicates sources are beyond 5 kpc.

Atomic gas resides in photo-dissociation regions related to HII regions.

Abstract

We present an HI absorption survey of the central 250 pc of the Galaxy. Very Large Array (VLA) observations were made at 21 cm in the DnC and CnB configurations and have a resolution of ~15"(0.6 pc at the Galactic Center (GC) distance) and a velocity resolution of ~2.5 km/s. This study provides HI data with high spatial resolution, comparable with the many high resolution observations which have been made of GC sources over the past ten years. Here we present an overview of the HI absorption toward ~40 well-known continuum sources and a detailed comparison of the ionized, atomic and molecular components of the interstellar medium for the Sgr B, Radio Arc and Sgr C regions. In these well-known regions, the atomic gas appears to be closely correlated in both velocity and distribution to the ionized and molecular gas, indicating that it resides in photo-dissociation regions related to the HII regions in the GC. Toward the majority of the radio continuum sources, HI absorption by the 3-kpc arm is detected, constraining these sources to lie beyond a 5 kpc distance in the Galaxy.