Large-Scale CO and [C I] Emission in the ρ Ophiuchi Molecular Cloud

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 resol...

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Bibliographic Details
Published in:The Astrophysical journal 2005-05, Vol.625 (1), p.194-209
Main Authors: Kulesa, Craig A, Hungerford, Aimee L, Walker, Christopher K, Zhang, Xiaolei, Lane, Adair P
Format: Article
Language:English
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Summary: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 1600 arcmin super(2) maps (2.3 pc super(2)) with 0.1 pc resolution in submillimeter CO (4 arrow right 3) and [C I] ( super(3)P sub(1) arrow right super(3)P sub(0)) line emission from the Antarctic Submillimeter Telescope and Remote Observatory (AST/RO) and pointed observations in the CO (7 arrow right 6) and [C I] ( super(3)P sub(2) arrow right super(3)P sub(1)) lines. Within the large-scale maps, smaller spectral line maps of 3000 AU resolution over similar to 90 arcmin super(2) (0.2 pc super(2)) of the cloud in CO, CS, HCO super(+), and their rare isotopomers are made at the Heinrich Hertz Telescope (HHT) in Arizona. Comparison of CO, HCO super(+), and [C I] maps with far-infrared observations of atomic and ionic species from the Infrared Space Observatory (ISO) far-infrared and submillimeter continuum emission and near-infrared H sub(2) emission allows clearer determination of the physical and chemical structure of the rho Oph PDR, since each species probes a different physical region of the cloud structure. Although a homogeneous plane-parallel PDR model can reproduce many of the observations described here, the excitation conditions needed to produce the observed HCO super(+) and [O I] emission imply inhomogeneous structure. Strong chemical gradients are observed in HCO super(+) and CS; the former is ascribed to a local enhancement in the H sub(2) ionization rate, and the latter is principally due to shocks. Under the assumption of a simple two-component gas model for the cloud, we find that [C II] and [C I] emission predominantly arises from the lower density envelopes (10 super(3)-10 super(4) cm super(-3)) that surround denser cloud condensations, or "clumps." The distribution of [C I] is very similar to that of C super(18)O and is generally consistent with illumination from the "far" side of the cloud. A notable exception is found at 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 HD 147889 and a total gas column density that follows that of C super(18)O, dec
ISSN:0004-637X
1538-4357
DOI:10.1086/426096