[C II] and [O I] Absorption and Self-Absorption Toward the Nessie Bubble
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Jim Jackson
SOFIA Science Center
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The Nessie Nebula is an iconic filamentary Infrared Dark Cloud with an aspect ratio of at least 80:1.  Its most active star forming region is a shell like bubble surrounding an H II region. I will describe SOFIA [C II] and [O I] observations of the bubble, along with ATCA and Mopra radio observations of free-free emission, recombination lines, ammonia, and HCO+. The Nessie Bubble is powered by a star cluster recently formed on its western edge. A luminous protostar has formed where the expanding Bubble collides with the Nessie IRDC filament. Bright [O I] emission in the Bubble’s PDR shows self-absorption features throughout the map arising from molecular gas in the shell.  [O I] toward the luminous protostar shows an inverse P Cygni profile, indicating collapse. Both [C II] and [O I] show absorption features toward the luminous protostar at a velocity corresponding to an unrelated, foreground molecular cloud. I will suggest that [C II] absorption and self-absorption is due to subthermally excited [C II] in the photodissociated “skin” of molecular clouds, whereas [O I] absorption and self-absorption is dominated by foreground molecular gas. Star formation in Nessie likely proceeds along the filament, and the interaction with the Bubble spawns new stars.

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