We measure H _ { 2 } temperatures and column densities across the Orion BN/KL explosive outflow from a set of thirteen near-IR H _ { 2 } rovibrational emission lines observed with the TripleSpec spectrograph on Apache Point Observatory ’ s 3.5-meter telescope .
We find that most of the region is well-characterized by a single temperature ( \sim 2000–2500 K ) , which may be influenced by the limited range of upper energy levels ( 6000–20,000 K ) probed by our data set .
The H _ { 2 } column density maps indicate that warm H _ { 2 } comprises 10 ^ { -5 } –10 ^ { -3 } of the total H _ { 2 } column density near the center of the outflow .
Combining column density measurements for co-spatial H _ { 2 } and CO at T = 2500 K , we measure a CO/H _ { 2 } fractional abundance of 2 \times 10 ^ { -3 } , and discuss possible reasons why this value is in excess of the canonical 10 ^ { -4 } value , including dust attenuation , incorrect assumptions on co-spatiality of the H _ { 2 } and CO emission , and chemical processing in an extreme environment .
We model the radiative transfer of H _ { 2 } in this region with UV pumping models to look for signatures of H _ { 2 } fluorescence from \ion H1 Ly \alpha pumping .
Dissociative ( J-type ) shocks and nebular emission from the foreground Orion \ion H2 region are considered as possible Ly \alpha sources .
From our radiative transfer models , we predict that signatures of Ly \alpha pumping should be detectable in near-IR line ratios given a sufficiently strong source , but such a source is not present in the BN/KL outflow .
The data are consistent with shocks as the H _ { 2 } heating source .