Velocity resolved Fabry-Perót imaging of molecular hydrogen emission in OMC-1
چکیده
We present a velocity resolved data cube of the distribution of the v=1-0 S(1) line of molecular hydrogen (H 2) from the source OMC-1. With ~ 1.5 arcsec spatial and 14 km s-1 velocity resolution, obtained with a scanning Fabry-Perót interferometer, it provides the most extensive database yet obtained on both the distribution and dynamics of the shocked molecular gas in this source. The line profiles are broad and generally smooth all over the source, with total extent (FWZI) up to ~ 150 km s-1. We have identified, however, two distinct components to the line profiles which have different spatial distributions. Over the entire source, strong emission from a central velocity component is present, close to the ambient cloud velocity, while emission from high velocity components (both red-and blue-shifted) is confined to discrete condensations. The central velocity component peaks, on average, at v LSR ~ +12 km s-1 , with an average FWHM of ~ 37 km s-1 , but shows subtle variation across the source. In particular, the strongest emission region, Peak 1 to the northwest , is both slightly blue-shifted and broader than the secondary Peak 2 to the southeast of OMC-1. We interpret this emission as the result of an isotropic steady wind from the IRc2 complex being loosely collimated by a disk, so that it flows close to the plane of the sky but with Peak 1 pointing slightly towards us, and interacting with ambient molecular gas to excite the H 2 emission. In addition, high velocity emission components (centred at ~-35 km s-1 and +40 km s-1 with FWHM of ~ 30 km s-1) are found in discrete locations, primarily along an emission ridge running north along the Peak 1 region and towards the circumstellar disk about the IRc2 complex. We develop an analytical shock model to demonstrate that these discrete emission knots closely resemble the emission expected from partially resolved bow-shocks. We ascribe these features as additional 'bullets' to those identified by Allen & Burton (1993) in [FeII] at greater distances from the source, but which have been revealed by their interaction with dense, ambient molecular gas. They likely originate from a temporally-limited event ≤ 1000 years ago. We provide new estimates on their energetics and momenta of all the bullets, and speculate on their origin.