Millimeter-wave Spectral Line Surveys toward the Galactic Circumnuclear Disk and Sgr A*

TL;DR

This study conducted extensive spectral line surveys of the Galactic circumnuclear disk and Sgr A* at 3 mm, detecting multiple molecular lines and classifying them based on their velocity profiles to understand nuclear environments.

Contribution

First unbiased spectral line survey at 3 mm toward the Galactic center, classifying molecular lines by velocity components to distinguish nuclear environments.

Findings

Detected 46 molecular lines from 30 species, including rare isotopomers.

Classified lines into CND-, GMC-, and HBD-types based on velocity profiles.

Provided line intensities and ratios to compare Galactic and extragalactic nuclei.

Abstract

We have performed unbiased spectral line surveys at 3 mm band toward the Galactic circumnuclear disk (CND) and Sgr A* using the Nobeyama Radio Observatory (NRO) 45 m radio telescope. The target positions are two tangential points of the CND and the direction of Sgr A*. We have obtained three wide-band spectra which cover the frequency range from 81.3 GHz to 115.8 GHz, detecting 46 molecular lines from 30 species including 10 rare isotopomers and four hydrogen recombination lines. Each line profile consists of multiple velocity components which arise from the CND, +50 km/s and +20 km/s clouds (GMCs), and the foreground spiral arms. We define the specific velocity ranges which represent the CND and the GMCs toward each direction, and classify the detected lines into three categories: the CND-/GMC-/HBD-types, based on the line intensities integrated over the defined velocity ranges. The CND- and GMC-types are the lines which mainly trace the CND and the GMCs, respectively. The HBD-type possesses the both characteristics of the CND-/GMC-types. We also present the lists of line intensities and other parameters, as well as intensity ratios, which must be useful to investigate the difference between nuclear environments of our Galaxy and of others.