Density Distribution of the Warm Ionized Medium

Type Conference Paper
Names Alex S. Hill, R. J. Reynolds, R. A. Benjamin, L. M. Haffner
Conference Name Bulletin of the American Astronomical Society
Volume 38
Pages 923
Date December 1, 2006
Library Catalog NASA ADS
Abstract Observations of Hα emission measures and pulsar dispersion measures at high Galactic latitude (|b| > 10°) provide information about the density and distribution of the diffuse warm ionized medium (WIM). We use data from the Wisconsin H-Alpha Mapper (WHAM) Northern Sky Survey. We have removed sightlines that intersect classical HII regions, leaving a sample of only the diffuse WIM. The diffuse WIM has a lognormal distribution of EM sin |b|, which is consistent with a density structure established by isothermal turbulence. A comparison of pulsar dispersion measures with emission measures shows that the H+ responsible for most of the emission along high-EM sightlines is clumped in high density (> 0.2 cm^-3) regions that occupy only of order 10 parsecs along the line of sight and contribute little to the total H+ column density, while the H+ along low-EM sightlines occupies hundreds of parsecs with densities of 0.03 0.1 cm^-3. We find an approximate power law relationship between local density of the gas and occupation length. WHAM is supported by NSF grant AST 02-04973.
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