Near-Infrared Spectroscopy of Molecular Filaments in the Reflection Nebula NGC 7023

Martini, P., Sellgren, K., and Hora, J.L. 1997, ApJ, 484, 296

We present near-infrared spectroscopy of fluorescent molecular hydrogen (H₂) emission from molecular filaments in the reflection nebula NGC 7023. We derive the relative column densities of H₂ rotational-vibrational states from the measured line emission and compare these results with several model photodissociation regions covering a range of densities, incident UV-fields, and excitation mechanisms. Our best-fit models for one filament suggest, but do not require, either a combination of different densities, suggesting clumps of 10⁶ cm^-3 in a 10⁴ - 10⁵ cm^-3 filament, or a combination of fluorescent excitation and thermally-excited gas, perhaps due to a shock from a bipolar outflow. We derive densities and UV fields for these molecular filaments that are in agreement with previous determinations.