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.
32
H 2 line emission in OMC-1, including one of
the famous “bullets” or “fingers,” as shown in
Figure 2. with shock speed, and thus it lends support
to the idea that the high temperature line
emission is from recently reformed H 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 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.
GeminiFocus
Tom Geballe is an astronomer at the Gemini
North Observatory. He can be reached at:
[email protected].
January 2018 / 2017 Year in Review