Figure 2.
Image of emisson
from the 1-0 S(1) line
of molecular hydrogen
in a portion of the
OMC-1 outflow in
the H 2 1–0 S(1) line
(from Bally et al., A&A,
579: A130, 2015)
with the GNIRS slit
superimposed. The
1.9-2.5-micron spectra
(published in Geballe,
Burton, & Pike, ApJ,
837: 83, 2017) at the
four positions denoted
by asterisks show
some of the same
weak, high-excitation
lines previously seen
in HH 7.
North to traverse several regions of intense
H 2 line emission in OMC-1, including one of
the famous “bullets” or “fingers,” as shown in
Figure 2.
The results are unequivocal — the high tem-
perature (5,000 K) component is present at
all analyzed locations along the slit. It thus
appears to be a common characteristic of
shock-excited molecular gas. In OMC-1 the
largest percentage of hot H 2 (still relatively
small at only about 3.3%) is in the “bullet” (a
dense and compact clump of gas piercing
the ambient molecular cloud at about 120
km/sec). This is consistent with the hypothe-
sis that the amount of dissociation increases
April 2017
with shock speed, and thus it lends support
to the idea that the high temperature line
emission is from recently reformed H 2 .
Future detailed modeling and laboratory
observations of the formation spectrum are
badly needed to compare with the observa-
tions. Burton, Pike, and I have plans to obtain
further observations of the high tempera-
ture H 2 at higher sensitivity and in both more
extreme and less extreme environments.
Tom Geballe is an astronomer at the Gemini
North Observatory. He can be reached at:
[email protected].
GeminiFocus
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