paper

Large Scale CO and [CI] emission in the rho Ophiuchi Molecular Cloud

arXiv:astro-ph/0408518 · doi:10.1086/426096

Abstract

We present a comprehensive study of the rho Ophiuchi molecular cloud that addresses aspects of the physical structure and condition of the molecular cloud and its photodissociation region (PDR) by combining far-infrared and submillimeter-wave observations with a wide range of angular scale and resolution. We present 40'x40' maps in CO(4-3) and [CI](3P1-3P0) line emission from the Antarctic Submillimeter Telescope and Remote Observatory (AST/RO), and pointed observations in the CO(7-6) and [CI](3P2-3P1) lines. Within, smaller spectral line maps of the cloud in CO, CS, HCO+ and their rare isotopomers are made at the Heinrich Hertz Submillimeter Telescope Observatory (HHT) in Arizona. Comparison with far-infrared and submillimeter continuum emission, and near-infrared H2 emission allows clearer determination of the physical and chemical structure of the rho Oph photodissociation region (PDR). The excitation conditions needed to produce the observed HCO+ and [OI] emission directly imply inhomogeneous structure. Strong chemical gradients are observed in HCO+ and CS; the former is ascribed to a local enhancement in the H2 ionization rate, the latter is principally due to shocks. The distribution of [CI] is very similar to C18O, and generally consistent with illumination from the 'far' side of the cloud. A notable exception is found at the the western edge of the cloud, where UV photons create a PDR viewed `edge-on'. The abundance of atomic carbon is accurately modeled using a radiation field that decreases with increasing projected distance from the exciting star HD147889. In contrast to conclusions of other studies, we find that no non-equilibrium chemistry is needed to enhance the atomic carbon abundance.

arXiv comment17 pages, 21 figures. To be published in the Astrophysical Journal. High resolution color version (PS, PDF formats) available at http://loke.as.arizona.edu/~ckulesa/research/publications/rhooph/

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