AAS 203rd Meeting, January 2004
Session 111 Interstellar Medium II
Poster, Thursday, January 8, 2004, 9:20am-4:00pm, Grand Hall

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[111.03] WHAM Observations of Ionized Gas in High-Velocity Interstellar Clouds

J. L. Reynolds, S. L. Tufte (Lewis & Clark College)

We have used the Wisconsin H-Alpha Mapper (WHAM) spectrometer to study the C complex of high-velocity interstellar clouds. High-velocity clouds (HVCs) have been well-studied in the 21-cm line of neutral hydrogen and are thought to be located in the galactic halo, but their origins and role in galactic evolution are unknown. We study H\alpha emission, which gives us information about the ionized hydrogen content of the clouds, and other emission lines that allow us to investigate the temperature, density and other conditions in the clouds.

The C complex has been studied extensively using ultraviolet absorption spectra from the FUSE and STIS instruments. By combining this information with our emission line data from the same sightlines, we can gain insight into the metallicity and other physical properties of the clouds. Our sightlines include PG1259+593, Mrk 817, Mrk 279, and PG1351+640. We measured H\alpha emission between 0.051 and 0.106 R in these directions. We placed 3\sigma upper limits on our nondetections of emission from [SII] \lambda6716, [NII] \lambda6583, and [OIII] \lambda5007 for all of the sightlines. We find a hydrogen ionizing flux of 1.1 x 105 to 2.2 x 105 photons cm-2. Our observations imply a hydrogen ionization fraction of 0.40 to 0.72, an electron density of 0.006 to 0.25 cm-3, and temperature upper limits of 10,000 to 20,000 K, with Mrk 817 possibly as low as 6,000 K. Our results are consistent with previous metallicity calculations of 0.10 to 0.26 solar. Such a small amount of heavy elements suggests an extragalactic origin for the C complex.

We acknowledge funding from the National Science Foundation through grant AST 02-06349, from a Research Corporation Cottrell College Science Award, and from the John S. Rogers Science Research Program at Lewis & Clark College.

The author(s) of this abstract have provided an email address for comments about the abstract: jlr@lclark.edu

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