Towards a three-dimensional distribution of the molecular clouds in the Galactic Centre

TL;DR

This paper constructs a three-dimensional model of molecular clouds in the Galactic Centre using CO and OH line data, revealing a bar-like structure with no ring evident.

Contribution

It introduces a novel method to accurately derive OH column density, excitation temperature, and optical depth from multiple OH lines, enabling detailed 3D mapping of molecular clouds.

Findings

Identifies a bar-like structure inclined at 67.5 degrees in the GC

Estimates total OH mass in the GC between 2400-5100 solar masses

Finds no evidence of a ring structure in the GC

Abstract

We present a study of the three-dimensional structure of the molecular clouds in the Galactic Centre (GC) using CO emission and OH absorption lines. Two CO isotopologue lines, $^{12}$CO ($J$=1$\rightarrow$0) and $^{13}$CO ($J$=1$\rightarrow$0), and four OH ground-state transitions, surveyed by the Southern Parkes Large-Area Survey in Hydroxyl (SPLASH), contribute to this study. We develop a novel method to calculate the OH column density, excitation temperature, and optical depth precisely using all four OH lines, and we employ it to derive a three-dimensional model for the distribution of molecular clouds in the GC for six slices in Galactic latitude. The angular resolution of the data is 15.5 arcmin, which at the distance of the GC (8.34 kpc) is equivalent to 38 pc. We find that the total mass of OH in the GC is in the range 2400-5100 Solar mass . The face-on view at a Galactic latitude of b = 0{\deg} displays a bar-like structure with an inclination angle of 67.5 $\pm$ 2.1{\deg} with respect to the line of sight. No ring-like structure in the GC is evident in our data, likely due to the low spatial resolution of the CO and OH maps.