NICMOS Observations of Shocked H2in Orion

Abstract

HST NICMOS narrowband images of the shocked molecular hydrogen emission in OMC-1 are analyzed to reveal new information on the BN/KL outflow. The outstanding morphological feature of this region is the array of molecular hydrogen fingers emanating from the general vicinity of IRc2 and the presence of several Herbig-Haro objects. The NICMOS images appear to resolve individual shock fronts. This work is a more quantitative and detailed analysis of our data from a previous paper. Line strengths for the H2 1-0 S(4) plus 2-1 S(6) lines at 1.89 μm are estimated from measurements with the Paschen-α continuum filter F190N at 1.90 μm and continuum measurements at 1.66 and 2.15 μm. We compare the observed H2 line strengths and ratios of the 1.89 and 2.12 μm 1-0 S(1) lines with models for molecular cloud shock waves. Most of the data cannot be fit by J-shocks but are well matched by C-shocks with shock velocities in the range of 20-45 km s-1 and preshock densities of 104-106 cm-3, similar to values obtained in larger beam studies which averaged over many shocks. There is also some evidence that shocks with higher densities have lower velocities.