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

We report SOFIA-upGREAT spectroscopic imaging of the [C II] 158 μm spectral line, as well as a number of [O I] 63 μm 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 μm, 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 μm 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.