Kavli Affiliate: Lile Wang
| First 5 Authors: Paul F. Goldsmith, Shengzhe Wang, Xin Wang, Raphael Skalidis, Gary A. Fuller
| Summary:
We report JWST MIRI/MRS observations of the H2 S(1) 17.04 micron transition
in two regions in the boundary of the Taurus Molecular Cloud. The two regions,
denoted Edge (near the relatively sharp boundary of the 13CO J=1-0 emission)
and Peak (the location of the strongest H2 emission observed with Spitzer),
have average intensities of 14.5 MJy/sr and 32.1 MJy/sr, respectively. We find
small scale structures of characteristic size 1.0 to 2.5 arcseconds,
corresponding to 140 AU to 350 AU, with characteristic intensity above the
extended background of 10 MJy/sr, corresponding to a J = 3 column density of
1.6×1017/cm2. The most plausible explanation for the observed intensities from
level 845 K above the J = 1 ortho-H2 ground state level is excitation by
collisions with H2 molecules (the hydrogen in this region being predominantly
molecular). Two mechanisms, turbulent dissipation and shocks, have been
proposed for heating of localized regions of the ISM to temperatures ~1000 K to
explain abundances of and emission from particular molecules. While we cannot
determine unique values of density and kinetic temperature, the solutions in
best agreement with predictions of shock models are H2 density = 370 /cm3 and
kinetic temperature = 1000 K. The total H2 column density of the small-scale
structures under these conditions is ~8×1017/cm2. This first direct detection
of heated tiny scale structure in the quiescent molecular interstellar medium
has significant implications for the physical structure of this phase of the
ISM and maintaining supersonic motions within it.
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