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Paper: The Fundamental Structure of UV-Irradiated Cloud Edges: Combined ALMA and IRAM-30m Observations of the Orion Bar
Volume: 499, Revolution in Astronomy with ALMA: The Third Year
Page: 185
Authors: Goicoechea, J.; Cuadrado, S.; Pety, J.; Ag'undez, M.; Cernicharo, J.; Chapillon, E.; Dumas, G.; Fuente, A.; Gerin, M.; Joblin, C.; Marcelino, N.; Müller, H.S.P.; Pilleri, P.
Abstract: The Orion Bar is the prototypical photodissociation region (PDR) exposed to a far-UV radiation field (FUV) of a few 104 times the mean interstellar field. Because of its proximity and nearly edge-on orientation, it provides a unique laboratory to study the physical and chemical gradients of a strongly FUV-illuminated molecular cloud. Using ALMA at ∼350 GHz, we have observed a field-of-view of ∼40”×40” toward the Orion Bar PDR consisting of a mosaic of 27 Nyquist-sampled pointings. These observations provide an unprecedented high angular resolution view (∼1” or ∼414 AU at the distance to Orion) of the most exposed molecular cloud edge. In addition, ACA and IRAM-30m maps were used to produce the short-spacing visibilities filtered out by the ALMA array. These interferometric observations complement a complete line survey we have carried out using the IRAM-30m telescope between ∼80 GHz and ∼360 GHz. Despite being a harsh environment, over 60 species with up to 6 atoms have been identified, including main isotopologues (D, 13C, 18O, 17O, 34S, 33S, and 15N). The first molecular line images of the Orion Bar obtained with ALMA at ∼1” resolution reveal the fundamental structure in density and temperature of the molecular gas as well as its complex kinematics at an unprecedented spatial resolution. This early data set also allowed us to compute corrected line frequencies for SH+, an interesting hydride tracing reactions of S+ with vibrationally excited H2 in the PDR edge.
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