Sagittarius B1 -- A Patchwork of H II Regions and PhotoDissociation
  Regions
  Sgr B1 is a luminous H II region in the Galactic Center immediately next to
the massive star-forming giant molecular cloud Sgr B2 and apparently connected
to it from their similar radial velocities. In 2018 we showed from SOFIA
FIFI-LS observations of the [O III] 52 and 88 micron lines that there is no
central exciting star cluster and that the ionizing stars must be widely spread
throughout the region. Here we present SOFIA FIFI-LS observations of the [O I]
146 and [C II] 158 micron lines formed in the surrounding photodissociation
regions (PDRs). We find that these lines correlate neither with each other nor
with the [O III] lines although together they correlate better with the 70
micron Herschel PACS images from Hi-GAL. We infer from this that Sgr B1
consists of a number of smaller H II regions plus their associated PDRs, some
seen face-on and the others seen more or less edge-on. We used the PDR Toolbox
to estimate densities and the far-ultraviolet intensities exciting the PDRs.
Using models computed with Cloudy, we demonstrate possible appearances of
edge-on PDRs and show that the density difference between the PDR densities and
the electron densities estimated from the [O III] line ratios is incompatible
with pressure equilibrium unless there is a substantial pressure contribution
from either turbulence or magnetic field or both. We likewise conclude that the
hot stars exciting Sgr B1 are widely spaced throughout the region at
substantial distances from the gas with no evidence of current massive star
formation.
