Quantitative optical and near-infrared spectroscopy of molecular hydrogen towards HH91A

TL;DR

This study presents detailed optical and near-infrared spectroscopy of molecular hydrogen in HH91A, revealing thermal excitation from slow shocks and ruling out UV-fluorescence, with extensive line detection and temperature analysis.

Contribution

It provides the first comprehensive optical and near-infrared spectral analysis of H_2 in HH91A, identifying thermal excitation mechanisms and detailed physical conditions.

Findings

Detected ~200 H_2 lines from v'=0 to 8

Gas temperature is mainly 2750 K, with 1% at 6000 K

Emission driven by slow non-dissociative J-shock

Abstract

Integral-field spectroscopy of molecular hydrogen in the optical wavelength region and complementary long-slit near-infrared spectroscopy are presented towards HH91A.The detection of some 200 H_2 lines arising from ro-vibrational levels up to v'=8 ranging between 7700A and 2.3 microns is reported. The emission arises from thermally excited gas where the bulk of the material is at 2750 K and where 1% is at 6000 K. The total column density of shocked gas is N(H_2) = 10^{18} cm^{-2}. Non-thermal excitation scenarios such as UV-fluorescence do not contribute to the excitation of H_2 towards HH91A. The emission is explained in terms of a slow non-dissociative J-shock which propagates into a low-density medium which has been swept-up by previous episodes of outflows which have occurred in the evolved HH90/91 complex.