The distribution of ionized, atomic and PDR gas around S1 in Rho Ophiuchus

Abstract

The early B star S1 in the Rho Ophiuchus cloud excites an HII region and illuminates a large egg-shaped photodissociation (PDR) cavity. The PDR is restricted to the west and south-west by the dense molecular Rho Oph A ridge, expanding more freely into the diffuse low density cloud to the north-east. We analyze new SOFIA GREAT, GMRT and APEX data together with archival data from Herschel/PACS, JCMT/HARPS to study the properties of the photo-irradiated ionized and neutral gas in this region. The tracers include [C II] at 158 micron, [O I] at 63 and 145 micron, J=6-5 transitions of CO and 13CO, HCO+ (4-3), radio continuum at 610 and 1420 MHz and HI at 21 cm. The PDR emission is strongly red-shifted to the south-east of the nebula, and primarily blue-shifted on the north western side. The [C II] and and [O I]63 spectra are strongly self-absorbed over most of the PDR. By using the optically thin counterparts, [13C II] and [O I]145 respectively, we conclude that the self-absorption is dominated by the warm (>80 K) foreground PDR gas and not by the surrounding cold molecular cloud. We estimate the column densities of C+ and O of the PDR to be 3e18 and 2e19 cm^-2, respectively. Comparison of stellar far-ultraviolet flux and reprocessed infrared radiation suggest enhanced clumpiness of the gas to the north-west. Analysis of the emission from the PDR gas suggests the presence of at least three density components consisting of high density (10^6 cm^-3) clumps, medium density (10^4 cm^-3) and diffuse (10^3 cm^-3) interclump medium. The medium density component primarily contributes to the thermal pressure of the PDR gas which is in pressure equilibrium with the molecular cloud to the west. We find that the PDR is tilted and warped with the south-eastern side of the cavity being denser on the front and the north-western side being denser on the rear.

15 pages, 15 figures, Accepted for publication in A&A

References in corpus (10)

• A Spitzer Survey of Young Stellar Clusters within One Kiloparsec of the Sun: Cluster Core Extraction and Basic Structural Analysis
• The Gould's Belt Distances Survey (GOBELINS) I. Trigonometric parallax distances and depth of the Ophiuchus complex
• The Electron Temperature Gradient in the Galactic Disk
• The upGREAT dual frequency heterodyne arrays for SOFIA
• The Spitzer c2d Survey of Large, Nearby, Interstellar Clouds: VII. Ophiuchus Observed with MIPS
• SEPIA - a new single pixel receiver at the APEX Telescope
• [CII] 158 μm self-absorption and optical depth effects
• High Spectral and Spatial Resolution Observations of the PDR Emission in the NGC2023 Reflection Nebula with SOFIA and APEX
• Opening the Treasure Chest in Carina
• Gas and dust in the star-forming region rho Oph A: II. The gas in the PDR and in the dense cores

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• Far-infrared line emission from the outer Galaxy cluster Gy 3-7 with SOFIA/FIFI-LS: Physical conditions and UV fields