SOFIA/EXES observations of warm H2 at high spectral resolution: II. IC443C, NGC2071, and 3C391

TL;DR

This study uses high-resolution SOFIA/EXES spectra to investigate velocity shifts between ortho- and para-H2 in shocked regions of three Galactic sources, exploring shock dynamics and molecular excitation.

Contribution

It provides the first velocity-resolved spectra of H2 in these sources and discusses potential reasons for the absence of expected velocity shifts in C-type shocks.

Findings

No reliable velocity shifts detected between ortho- and para-H2.

Possible explanations include high initial ortho-to-para ratios and complex shock structures.

Results suggest shock conditions may differ from previous models.

Abstract

Using the EXES instrument on SOFIA, we have obtained velocity-resolved spectra of several pure rotational lines of H2 toward shocked molecular gas within three Galactic sources: the supernova remnant (SNR) IC443 (Clump C), a protostellar outflow in the intermediate-mass star-forming region NGC 2071, and the SNR 3C391. These observations had the goal of searching for expected velocity shifts between ortho- and para-H2 transitions emitted by C-type shocks. In contrast in our previous similar study of HH7, the result of our search was negative: no velocity shifts were reliably detected. Several possible explanations for the absence of such shifts are discussed: these include a preshock ortho-to-para ratio that is already close to the high-temperature equilibrium value of 3 (in the case of IC443C), the more complex shock structures evident in all these sources, and the larger projected aperture sizes relative to those in the observations of HH7.