First Detection of Submillimeter [C I] Emission in the Small Magellanic Cloud

Abstract

We report the first detection of [CI] (3P1-3P0) emission at 609 um in a region of the Small Magellanic Cloud (N27). Environments poor in heavy elements and dust such as the SMC are thought to be dominated by photodissociation regions. This is the lowest metallicity source where submillimeter neutral carbon emission has been detected. Studying the [CI]/CO intensity ratio in several sources spanning more than an order of magnitude in metallicity, Z, we find that the [CI]/CO ratio increases for decreasing Z. The existence of such a trend points to a photodissociation origin for most of neutral carbon in molecular clouds, in agreement with standard PDR models. We also report ISO FIR spectroscopic observations of N27, and use them to derive its physical properties. Comparison between the density and radiation field revealed by FIR diagnostics (n~300-1000 cm-3, Xuv~30-100 Xo) and those derived from millimeter and submillimeter data (n~10^5 cm-3, Xuv<30 Xo) suggests that the FIR lines originate in more diffuse gas, and are perhaps dominated by the interclump medium. Regardless of the cause, analysis of the FIR and mm-submm data produces a discrepancy of two orders of magnitude for the density of this source.

12 pages including 1 table and 2 figures, using AASTEX macros v4.0, to appear in The Astrophysical Journal Letters

References in corpus (3)

• Far Infrared and Submillimeter Emission from Galactic and Extragalactic Photo-Dissociation Regions
• A semianalytical model for the observational properties of the dominant carbon species at different metallicities
• Submillimeter observations of IC 10: the dust properties and neutral carbon content of a low metallicity starburst

Cited by in corpus (10)

• The Spitzer Survey of the Small Magellanic Cloud: FIR Emission and Cold Gas in the SMC
• The CI lines as tracers of molecular gas, and their prospects at high redshifts
• The Properties of the Interstellar Medium within a Star-Forming Galaxy at z=2.3
• AST/RO Observations of Atomic Carbon near the Galactic Center
• Molecular line intensities as measures of cloud masses - II. Conversion factors for specific galaxy types
• Velocity profiles of [CII], [CI], CO, and [OI] and physical conditions in four star-forming regions in the Large Magellanic Cloud
• Thermal Pressures in the Interstellar Medium of the Magellanic Clouds
• Physical conditions of the molecular gas in metal-poor galaxies
• CI and CO in Nearby Spiral Galaxies -- I. Line Ratio and Abundance Variations at ~ 200 pc Scales
• Atomic Carbon [CI]${(}^3{P}_1{-}^3{P}_0)$ Mapping of the Nearby Galaxy M83