# Kinematics and properties of the Central Molecular Zone as probed with [C II]

## TL;DR

This study maps the [C II] 158-micron line in the Galactic Central Molecular Zone to analyze ionized gas features, dynamics, and physical conditions, providing insights into the complex interstellar medium near the galactic center.

## Contribution

It presents high-resolution [C II] observations of the CMZ, revealing the distribution and dynamics of ionized and UV-irradiated gas, and compares these with other tracers to understand the region's physical properties.

## Key findings

- [C II] traces dense PDRs and ionized gas in the CMZ.
- The data reveal the spatial-velocity structure of gas streams and clouds.
- [C II] emission correlates with features like the Brick and Sgr A/Sgr B2.

## Abstract

The Galactic Central Molecular Zone (CMZ) is a region containing massive and dense molecular clouds, with dynamics driven by a variety of energy sources including a massive black hole. It is thus the nearest template for understanding physical processes in extragalactic nuclei. The CMZ's neutral interstellar gas has been mapped spectrally in many neutral atomic and molecular gas tracers, but the ionized and CO-dark H2 regions are less well traced spectroscopically. We mapped the fine structure line of C+ at 158 microns, [C II], to identify and characterize features of the ionized gas in the CMZ, including UV irradiated neutral gas, photon dominated regions (PDRs), CO-dark H2 gas, and highly ionized gas. We observed the [C II] 158-micron fine structure line with high spectral resolution using Herschel HIFI with two perpendicular On-the-Fly strip scans, along l = -0.8 to +0.8 and b = -0.8 to +0.8, both centered on (l,b) = (0,0). We analyzed the spatial-velocity distribution of the [C II] data and compared them to those of [C I] and CO, and to dust continuum maps, in order to determine the properties and distribution of the UV irradiated gas and its dynamics within the CMZ. The longitude- and latitude-velocity maps of [C II] trace portions of the orbiting open gas streams of dense molecular clouds, the cloud G0.253+0.016, also known as the Brick, the Arched Filaments, and the ionized gas near Sgr A and Sgr B2. We use the [C II] and auxiliary data to determine the physical and dynamical properties of these CMZ features. The [C II] emission arises primarily from dense PDRs and highly ionized gas, and is an important tracer of the kinematics and physical conditions of this gas.