3-D CMZ I: Central Molecular Zone Overview

Abstract

The Central Molecular Zone (CMZ) is the largest reservoir of dense molecular gas in the Galaxy and is heavily obscured in the optical and near-IR. We present an overview of the far-IR dust continuum, where the molecular clouds are revealed, provided by Herschel in the inner 40°($|l|<$ 20°) of the Milky Way with a particular focus on the CMZ. We report a total dense gas ($N$(H${}_2$) $>10^{23}$ cm${}^{-2}$) CMZ mass of M=$2\begin{array}{c}+2\\ -1\end{array}\times 10^7$ M${}_{\odot }$ and confirm that there is a highly asymmetric distribution of dense gas, with about 70-75% at positive longitudes. We create and publicly release complete fore/background-subtracted column density and dust temperature maps in the inner 40°($|l|<$ 20°) of the Galaxy. We find that the CMZ clearly stands out as a distinct structure, with an average mass per longitude that is at least $3\times$ higher than the rest of the inner Galaxy contiguously from 1.8°$>\ell >$ -1.3°. This CMZ extent is larger than previously assumed, but is consistent with constraints from velocity information. The inner Galaxy's column density peaks towards the SgrB2 complex with a value of about 2 $\times$ 10${}^{24}$ cm${}^{-2}$, and typical CMZ molecular clouds are about N(H${}_2$)=10${}^{23}$ cm${}^{-2}$. Typical CMZ dust temperatures range from about $12-35$ K with relatively little variation. We identify a ridge of warm dust in the inner CMZ that potentially traces the base of the northern Galactic outflow seen with MEERKAT.

Accepted to ApJ, 17 pages, project website: https://centralmolecularzone.github.io/3D_CMZ/