GeminiFocus 2017 Year in Review | Page 34

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