EAS Publications Series
Volume 56, 2012The Role of the Disk-Halo Interaction in Galaxy Evolution: Outflow vs. Infall?
|Page(s)||257 - 265|
|Section||The Active Disk-Halo Connection: Infall vs. Outflows|
|Published online||17 September 2012|
Miguel A. de Avillez (ed)
EAS Publications Series, 56 (2012) 257–265
High-velocity clouds and extended gaseous galactic halos
Department of Astronomy, University of Wisconsin, 475 N. Charter St., Madison, WI 53705, USA ;
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.
© EAS, EDP Sciences, 2012