Kinematics and properties of the central molecular zone as probed with [C ii]

Abstract

Context. 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 H 2 regions are less well traced spectroscopically. Aims. To identify features of the UV irradiated neutral gas, photon dominated regions (PDRs) and CO-dark H 2 , and highly ionized gas in the CMZ as traced by the fine structure line of C + at 158 µm, [C ii], and to characterize their properties. Methods. We observed the [C ii] 158 µm 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) = (0We analyze the spatial-velocity distribution of the [C ii] data, compare them to those of [C i] and CO, and to dust continuum maps, in order to determine the properties and distribution of the ionized and neutral gas and its dynamics within the CMZ. Results. 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, the ionized gas within several pc of Sgr A and Sgr B2, and the Warm Dust Bubble. We use the [C ii] data to determine the physical and dynamical properties of these CMZ features. Conclusions. The bright far-IR 158 µm C + line, [C ii], when observed with high spatial and spectral resolution, traces a wide range of emission features in the CMZ. 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.

Ubiquitous velocity fluctuations throughout the molecular interstellar medium

“….1, and is associated both with a series of quasiregularly spaced molecular cloud condensations and an oscillatory pattern in the centroid velocity of the molecular gas. This velocity pattern is observed in multiple tracers, 10,13,84,85 indicating that it is of dynamical origin, and not simply the result of excitation or optical depth effects. Extended Data Figure 2d displays the Herschel-derived column density map (C. Battersby et al, manuscript in preparation) covering the region that displays the coherent velocity oscillation investigated in Ref.…”

Regulating Star Formation in Nearby Dusty Galaxies: Low Photoelectric Efficiencies in the Most Compact Systems

“…Thus, the scatter above and below the best-fit trend may be partially due to sources with an excess of hot dust continuum emission in their mid-IR spectra. This may be due to a weak, deeply buried AGN, even in sources where L IR is dominated by star formation, which in turn may change the ionization structure and the PAH properties (Voit 1992;Langer & Pineda 2015;Langer et al 2017). Alternatively, these objects may harbor heavily obscured star-forming regions with high levels of line self-absorption and/or continuum opacities.…”

Electron Densities and Nitrogen Abundances in Ionized Gas Derived Using [N ii] Fine-structure and Hydrogen Recombination Lines

“…We also included in our analysis the GOT C+ LOS, G030.0+0.0, that was observed with SOFIA/GREAT and presented by Langer et al (2017b). The angular resolution of these observations is 20 .…”