Spatial variation in temperature and density in the IC 63 PDR from Spectroscopy
arXiv:2110.11703 · doi:10.3847/1538-4357/ac2eb7
Abstract
We have measured the gas temperature in the IC 63 photodissociation region (PDR) using the S(1) and S(5) pure rotation lines of molecular hydrogen with SOFIA/EXES. We divide the PDR into three regions for analysis based on the illumination from Cas: "sunny," "ridge" and "shady." Constructing rotation diagrams for the different regions, we obtain temperatures of T= K towards the "ridge" and T= K in the "shady" side. The H emission was not detected on the "sunny" side of the ridge, likely due to the photo-dissociation of H in this gas. Our temperature values are lower than the value of T=68568 K using the S(1), S(3), and S(5) pure rotation lines, derived by Thi et al. (2009) using lower spatial-resolution ISO-SWS data at a different location of the IC 63 PDR. This difference indicates that the PDR is inhomogeneous and illustrates the need for high-resolution mapping of such regions to fully understand their physics. The detection of a temperature gradient correlated with the extinction into the cloud, points to the ability of using H pure rotational line spectroscopy to map the gas temperature on small scales. We used a PDR model to estimate the FUV radiation and corresponding gas densities in IC 63. Our results shows the capability of SOFIA/EXES to resolve and provide detailed information on the temperature in such regions.
10 pages, 4 figures