Distances to Galactic high-velocity clouds. I. Cohen Stream, complex GCP, cloud g1 - AstrophysicsReport as inadecuate

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Abstract: The high- and intermediate-velocity interstellar clouds HVCs-IVCs aretracers of energetic processes in and around the Milky Way. Clouds withnear-solar metallicity about one kpc above the disk trace the circulation ofmaterial between disk and halo the Galactic Fountain. The Magellanic Streamconsists of gas tidally extracted from the SMC, tracing the dark matterpotential of the Milky Way. Several other HVCs have low-metallicity and appearto trace the continuing accretion of infalling intergalactic gas. Theseassertions are supported by the metallicities 0.1 to 1 solar measured forabout ten clouds in the past decade. Direct measurements of distances to HVCshave remained elusive, however. In this paper we present four new distancebrackets, using VLT observations of interstellar \CaII H and K absorptiontoward distant Galactic halo stars. We derive distance brackets of 5.0 to 11.7kpc for the Cohen Stream likely to be an infalling low-metallicity cloud, 9.8to 15.1 kpc for complex GCP also known as the Smith Cloud or HVC40-15+100 andwith still unknown origin, 1.0 to 2.7 kpc for an IVC that appears associatedwith the return flow of the Fountain in the Perseus Arm, and 1.8 to 3.8 kpc forcloud g1, which appears to be in the outflow phase of the Fountain. Ourmeasurements further demonstrate that the Milky Way is accreting substantialamounts of gaseous material, which influences the Galaxy-s current and futuredynamical and chemical evolution.

Author: B.P. Wakker Wisconsin, D.G. York Chicago, R. Wilhelm Texas Tech, J.C. Barentine Texas, P. Richter Potsdam, T.C. Beers Michigan St

Source: https://arxiv.org/

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