SOFIA-upGREAT imaging spectroscopy of the [C II] 158um fine structure
  line of the Sgr B region in the Galactic center
  We report SOFIA-upGREAT spectroscopic imaging of the [C II] 158um spectral
line, as well as a number of [O I] 63um spectra, across a 67x45 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 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), the
G0.6-0.0 HII 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], 70um, and 20cm emission 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 160um continuum. Stars from regions of local star formation
likely dominate the UV field. Photodissociation regions and HII 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
ultra-luminous galaxies can be tested.
