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标题：Kinematics of the Horsehead Nebula and IC 434 Ionization Front in CO and C+
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作者：John Bally ; Ed Chambers ; Viviana Guzman 等
期刊名称：The Astronomical journal
印刷版ISSN：0004-6256
电子版ISSN：1538-3881
出版年度：2018
卷号：155
期号：2
页码：1-21
DOI：10.3847/1538-3881/aaa248
语种：English
出版社：American Institute of Physics
摘要：Stratospheric Observatory for Infrared Astronomy [C II] 157 μm, APEX 860 μm J=3−2 CO, and archival James Clerk Maxwell Telescope J =2−1 CO and 13CO observations of the Horsehead Nebula are presented. The photon-dominated region (PDR) between the Orion B molecular cloud and the adjacent IC434 H II region is used to study the radial velocity structure of the region and the feedback impacts of UV radiation. Multiple west-facing cloud edges are superimposed along the line of sight with radial velocities that differ by a few kilometers per second. The Horsehead lies in the foreground blueshifted portion of the Orion B molecular cloud and is predominantly illuminated from the rear. The mean H2 density of the Horsehead, ~6 ´ 103 cm-3, results in a spatially thin PDR where the photoablation flow has compressed the western cloud edge to an H2 density of (2–6) ´ 104 cm-3. The associated [C II] 157 μm layer has a width L<0.05 pc. The background parts of the Orion B cloud in the imaged field consist of a clumpy medium surrounded by molecular gas with H2 densities lower by one to two orders of magnitude. Along the straight part of the IC434 ionization front, the PDR layer probed by [C II] 157 μm emission is much thicker with L∼0.5 pc. A possible model for the formation and evolution of this edge-on ionization front and PDR is presented. The [C II] data were independently analyzed and published by Pabst et al.
关键词：H II regions;ISM: individual objects (Horsehead Nebula, Barnard 33);ISM: kinematics and dynamics;photon-dominated region (PDR)