The AMANOGAWA-2SB Galactic Plane Survey I: Data on the Galactic Equator

TL;DR

This paper presents a comprehensive survey of molecular gas in the Galactic plane using simultaneous observations of CO lines, revealing correlations and physical constraints on molecular gas properties across the galaxy.

Contribution

First large-scale simultaneous CO J=2-1 and J=1-0 survey of the Galactic plane, analyzing line ratios and correlations to infer molecular gas conditions.

Findings

Linear correlation between 12CO(J=1-0) and 12CO(J=2-1) intensities.

Curved correlation between 12CO(J=2-1) and 13CO(J=2-1) intensities.

Constraints on molecular gas physical conditions derived from radiative transfer analysis.

Abstract

Using a waveguide-type sideband-separating receiver (2SB receiver) on the Tokyo-NRO 60-cm telescope (renamed the AMANOGAWA telescope), we carried out simultaneous observations in the 12CO(J = 2-1) and 13CO(J = 2-1) lines over the Galactic plane l = 10-245 deg along b = 0 deg with a 3.75 arcmin grid. Using the 12CO(J = 1-0) data of Dame et al. (2001), who used a beam size almost the same as ours, we show 12CO(J = 2-1)/12CO(J = 1-0) and 13CO(J = 2-1)/12CO(J = 2-1) intensity ratios on the l-v map and the intensity correlations among the three lines. As a result, a linear correlation between 12CO(J = 1-0) and 12CO(J = 2-1) and a curve correlation between 12CO(J = 2-1) and 13CO(J = 2-1), as produced by most of the data, are found. We investigate these correlations with simple radiative transfer equations to ascertain a number of restrictions on the physical quantities of molecular gas on a galactic scale.