Abstract:
We used high-resolution [C II] 158 μm mapping of two nebulae IC 59 and IC 63 from SOFIA/upGREAT in
conjunction with ancillary data of the gas, dust, and polarization to probe the kinematics, structure, and magnetic
properties of their photodissociation regions (PDRs). The nebulae are part of the Sh 2-185 H II region that is
illuminated by the B0 IVe star γ Cas. The velocity structure of each PDR changes with distance from γ Cas, which
is consistent with driving by the radiation. Based on previous far-ultraviolet (FUV) flux measurements of, and the
known distance to, γ Cas, along with the predictions of 3D distances to the clouds, we estimated the FUV radiation
field strength (G0) at the clouds. Assuming negligible extinction between the star and clouds, we find their 3D
distances from γ Cas. For IC 63, our results are consistent with earlier estimates of distance from Andersson et al.,
locating the cloud at ∼2 pc from γ Cas at an angle of 58° to the plane of the sky behind the star. For IC 59, we
derive a distance of 4.5 pc at an angle of 70° in front of the star. We do not detect any significant correlation
between the orientation of the magnetic field and the velocity gradients of [C II] gas, which indicates a moderate
magnetic field strength. The kinetic energy in IC 63 is estimated to be an order of 10 higher than the magnetic
energies. This suggests that kinetic pressure in this nebula is dominant.
