High-velocity clouds and extended gaseous galactic halos

Type Conference Paper
Names B. P. Wakker
Proceedings Title EAS Publications Series
Conference Name EAS Publications Series
Volume 56
Pages 257-265
Date September 1, 2012
DOI 10.1051/eas/1256042
ISBN 1633-4760
URL http://adsabs.org/2012EAS.56.257W
Library Catalog labs.adsabs.harvard.edu
Abstract This contribution summarizes some recent results concerning gas in Galaxy halos. In the past few years, distances have been determined for six high-velocity clouds (HVCs), including the second largest, complex C. The derived distances range from about 2 to 10 kpc, placing these HVCs in the near Galactic halo, but far above the Galactic plane. Distances of ˜10 kpc were determined to three different concentrations in Complex C, implying a mass of ˜5 × 107M⊙; this cloud is known to have a metallicity of ˜0.15 solar, and represents an inflow of 0.15-0.25 M⊙ yr-1 of low-metallicity material. A statistical analysis of the sky and velocity distribution of the ˜200 small HVCs shows that they probably form a population of clouds orbiting the Milky Way, with distances up to 80 kpc, and a radial inflow component of 50 km s-1. A study of 115 Lyα and 14 O VI absorption lines at redshifts z < 0.017 (v < 5000 km s-1) in the spectra of 76 AGNs shows that half of the intergalactic Lyα absorption lines originate within 450 kpc of galaxies. The amount of gas inside this distance is a factor 2-4 more than the total amount of mass inside the galaxies.
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