SOFIA-upGREAT Imaging Spectroscopy of the [C ii] 158 μm Fine-structure Line of the Sgr B Region in the Galactic Center

Abstract

We report SOFIA-upGREAT spectroscopic imaging of the [C ii ] 158 μ m spectral line, as well as a number of [O i ] 63 μ m spectra, across a 67 × 45 pc field toward the Sgr B region in our Galactic center. The fully sampled and velocity-resolved [C ii ] images have 0.55 pc spatial and 1 km s −1 velocity resolutions. We find that Sgr B extends as a coherent structure spanning some 34 pc along the Galactic plane. Bright [C ii ] emission encompasses Sgr B1 (G0.5–0.0) and the G 0.6–0.0 H ii region and passes behind and beyond the luminous star-forming cores toward Sgr B2 (G0.7–0.0). Sgr B is a major contributor to the entire Galactic center’s [C ii ] luminosity, with surface brightness comparable to [C ii ] from the Arches region. [C ii ], 70 μ m, and 20 cm emissions share nearly identical spatial distributions. Combined with the lack of [C ii ] self-absorption, this indicates that these probes trace UV on the near surfaces of more extended clouds visible in CO isotopologues and 160 μ m continuum. Stars from regions of local star formation likely dominate the UV field. Photodissociation regions and H ii regions contribute similar amounts of [C ii ] flux. The extreme star formation cores of Sgr B2 contribute negligible amounts to the total [C ii ] intensity from the Sgr B region. Velocity fields and association with a narrow dust lane indicate that they may have been produced in a local cloud–cloud collision. The cores are likely local analogs of the intense star formation regions where ideas to explain the “C + deficit” in ultraluminous galaxies can be tested.