A Limit on the Metallicity of Compact High Velocity Clouds

Abstract

There is a fortuitous coincidence in the positions of the quasar TonS210 and the compact H I high velocity cloud CHVC224.0-83.4-197 on the sky. Using Far Ultraviolet Spectroscopic Explorer observations of the metal-line absorption in this cloud and sensitive H I 21cm emission observations obtained with the multibeam system at Parkes Observatory, we determine a metallicity of (O/H) <0.46 solar at a confidence of 3 sigma. The metallicity of the high velocity gas is consistent with either an extragalactic or Magellanic Cloud origin, but is not consistent with a location inside the Milky Way unless the chemical history of the gas is considerably different from that of the interstellar medium in the Galactic disk and halo. Combined with measurements of highly ionized species (C III and O VI) at high velocities, this metallicity limit indicates that the cloud has a substantial halo of ionized gas; there is as much ionized gas as neutral gas directly along the Ton S210 sight line. We suggest several observational tests that would improve the metallicity determination substantially and help to distinguish between possible origins for the high velocity gas. Additional observations of this sight line would be valuable since the number of compact HVCs positioned in front of background sources bright enough for high resolution absorption-line studies is extremely limited.

15 pages, 3 postscript figures + 1 JPEG figure (reduced from postscript for size considerations), accepted for publication in ApJ (June 2002)

References in corpus (6)

• HIPASS High-Velocity Clouds: Properties of the Compact and Extended Populations
• Abundances of Deuterium, Oxygen, and Nitrogen in the Local Interstellar Medium: Overview of First Results from the Far Ultraviolet Spectroscopic Explorer Mission
• The Diversity of High- and Intermediate-Velocity Clouds: Complex C versus IV Arch
• High-Velocity Cloud Complex C: Galactic Fuel or galactic Waste?
• HI spectra and column densities toward HVC and IVC probes
• Arecibo imaging of compact high-velocity clouds

Cited by in corpus (21)

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• The Magellanic Stream: Circumnavigating the Galaxy
• The COS/UVES Absorption Survey of the Magellanic Stream. III: Ionization, Total Mass, and Inflow Rate onto the Milky Way
• Atomic Hydrogen Gas in Dark-Matter Minihalos and the Compact High Velocity Clouds
• Deriving the Metallicity Distribution Function of Galactic Systems
• A population of weak metal-line absorbers surrounding the Milky Way
• Metal-Ion Absorption in Conductively Evaporating Clouds
• Contrasting the chemical evolution of the Milky Way and Andromeda galaxies
• The high-velocity clouds and the Magellanic Clouds
• Absorption Line Study of Halo Gas in NGC 3067 Toward the Background Quasar 3C 232
• The Milky Way halo as a QSO absorption-line system. New results from an HST/STIS absorption-line catalogue of Galactic high-velocity clouds
• The Cosmological Significance of High-Velocity Cloud Complex H
• The Surprisingly Constant Strength of O VI Absorbers over Cosmic Time
• Geometrodynamical Distances to the Galaxy's Hydrogen Streams
• High velocity clouds in the Galactic All Sky Survey I. Catalogue
• Photoionized Gas in Dark-Matter Minihalos in the Galactic Halo and Local Group
• The HI Column Density Distribution of the Galactic Disk and Halo
• Searching for Stars in Compact High-Velocity Clouds. II
• Do High-Velocity Clouds trace the Dark Matter subhalo population?
• A Compact High Velocity Cloud near the Magellanic Stream: Metallicity and Small-Scale Structure
• Mini High Velocity Clouds