Near-Infrared Imaging and [O I] Spectroscopy of IC 443 using Two Micron All Sky Survey and Infrared Space Observatory
We present near-infrared J (1.25 μm), H (1.65 μm), and Ks (2.17 μm) imaging of the entire supernova remnant IC 443 from the Two Micron All Sky Survey (2MASS), and Infrared Space Observatory (ISO) LWS observations of [O I] for 11 positions in the northeast. Near-infrared emission from IC 443 was detected in all three bands from most of the optically bright parts of the remnant, revealing a shell-like morphology, with bright Ks-band emission along the southern ridge and bright J and H along the northeastern rim. The total luminosity within the 2MASS bands is 1.3×1036 ergs s-1. These data represent the first near-infrared images that are complete in coverage of the remnant. The color and morphological structure are very different between the northeastern and southern parts. J- and H-band emission from the northeast rim is comparably bright and can be explained mostly by [Fe II] line emission. The hydrogen recombination lines, Pβ and Br10, should also be present in the broadband images, but probably contribute less than 10% of the J- and H-band fluxes. Strong [O I] (63 μm) lines were detected crossing the northeastern rim, with the strongest line in the northeastern shell where the near-infrared emission shows filamentary structure. In contrast, the southern ridge is dominated by Ks-band light exhibiting a clumped and knotty structure. A two excitation temperature model derived from previous ISO and ground-based observations predicts that H2 lines can explain most of Ks band and at least half of J- and H-band emission. Hence, the prominent broadband color differences arise from physically different mechanisms: atomic fine structure lines along the northeastern rim and molecular rovibrational lines along the southern ridge. Shock models imply a fast J-shock with vs~100 km s-1 and 10<no<103cm-3 for the northeastern rim and a slow C-shock with vs~30 km s-1 and no~104 cm-3 for the southern ridge, respectively. The shocked H2 line emission is well known from the southern sinuous ridge, produced by an interaction with dense molecular clouds. The large field of view and color of the 2MASS images show that the Ks-band emission extends to the east and the northeast, suggesting that the interaction extends to the inner part of the northeastern shell. Our new CO map of the inner part of the northeast quadrant shows good correspondence with the Ks-band map. The CO lines are broad, confirming that the Ks-band emission is due to shocked H2.