Wide-Field Molecular Line Mapping of the Nessie Nebula: an Extremely Filamentary Infrared Dark Cloud.

We present new ~90 GHz molecular line maps, taken with the Mopra 22 m telescope in Australia, of the Nessie Nebula, an extremely filamentary infrared dark cloud. The new images at ~38'' resolution cover over a degree (~100 pc) along the filament. Feedback from embedded stars alters the chemistry and creates molecular bubbles. The HCO+1-0 line profiles toward the associated clumps are asymmetric, with stronger blueshifted emission and fainter redshifted emission relative to the systemic velocity, as determined from the optically thin N2H+ 1-0 line. These asymmetryies arise from infall motions due to gravitational collapse. Collapse motions are confirmed by a new indicator of collapse, the [O I] 63 um line observed by SOFIA at high spectral resolution. Toward the brightest star forming region in Nessie, the [O I] profiles show redshifted absorption (inverse P Cygni) or self-absorption features. These collapse motions may indicate that the entire filament is collapsing inward. Future SOFIA measurements of Nessie and other filamentary IRDCs will shed light on the interplay of magnetic fields, gravitational collapse, and feedback in the densest, most-massive filaments.