Physics and Chemistry of Radiation Driven Cloud Evolution. [C ii] Kinematics of IC 59, and IC 63

Abstract

We used high-resolution [C ii ] 158 μ m 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 ( G _0 ) 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.

Keywords

• Nebulae
• Interstellar dust