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