Distances to Galactic High-Velocity Clouds. I. Cohen Stream, Complex GCP, Cloud g1

By B. Wakker, D. York, R. Wilhelm, John C. Barentine, P. Richter, Timothy C. Beers, Željko Ivezic´, J. Howk. 2007

146 citations recorded by the source corpus.

The high- and intermediate-velocity interstellar clouds (HVCs/IVCs) are tracers of energetic processes in and around the Milky Way. Clouds with near-solar metallicity about 1 kpc above the disk trace the circulation of material between disk and halo (the Galactic fountain). The Magellanic Stream consists of gas tidally extracted from the SMC, tracing the dark matter potential of the Milky Way. Several other HVCs have low metallicity and appear to trace the continuing accretion of infalling intergalactic gas. These assertions are supported by the metallicities (0.1 to 1 solar) measured for about 10 clouds in the past decade. Direct measurements of distances to HVCs have remained elusive, however. In this paper we present four new distance brackets, using VLT observations of interstellar Ca II H and K absorption toward distant Galactic halo stars. We derive distance brackets of 5.0 to 11.7 kpc for the Cohen Stream (likely to be an infalling low-metallicity cloud), 9.8 to 15.1 kpc for Complex GCP (also known as the Smith Cloud or HVC 40–15+100 and with still unknown origin), 1.0 to 2.7 kpc for an IVC that appears associated with the return flow of the fountain in the Perseus arm, and 1.8 to 3.8 kpc for cloud g1, which appears to be in the outflow phase of the fountain. Our measurements further demonstrate that the Milky Way is accreting substantial amounts of gaseous material, which influences the Galaxy’s current and future dynamical and chemical evolution.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/b0188794c02ea2715862c68a74ca7709120cc4e2

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Citations in the corpus

A BUDGET AND ACCOUNTING OF METALS AT z ∼ 0: RESULTS FROM THE COS-HALOS SURVEY (2013, background): “These discrete gas clouds lie mostly within ∼ 10 kpc of the Galactic plane (Wakker et al. 2007, 2008; Thom et al. 2008; Hsu et al. 2011).”
Gaseous Galaxy Halos (2012, methodology): “Most of the complexes are at distances between 2-15 kpc and z-heights <∼ 10 kpc (Wakker et al., 2008; Thom et al., 2006, 2008; Wakker et al., 2007, Wakker et al., in prep.)”
HI holes and high-velocity clouds in the spiral galaxy NGC 6946 (2008, background): “In the Milky Way, halo gas components are the well-known Intermediate-Velocity Clouds (IVCs) and, as conclusively shown by recent distance determinations (Wakker et al. 2007, 2008), also the High-Velocity Clouds (HVCs) (Wakker & van Woerden 1997).”
Star formation sustained by gas accretion (2014, background): “Extra-planar gas is also found in our own galaxy, where the existence of gas clouds falling in is long known (Oort 1966; Blitz et al. 1999; van Woerden et al. 2004; Wakker et al. 2007, 2008).”
Accretion of gas on to nearby spiral galaxies (2008, background): “New distance estimates for the large HVC complexes show that they are located in the upper halo of the Milky Way and have masses of order 106−7 M⊙ (Wakker et al. 2007a, 2008).”
Figuring Out Gas & Galaxies in Enzo (FOGGIE). I. Resolving Simulated Circumgalactic Absorption at 2 ≤ z ≤ 2.5 (2018, background): “Given how relatively close to the disk most HVCs are (e.g., Wakker et al. 2007, 2008; Thom et al. 2008; Lehner & Howk 2011; Lehner et al. 2012), these clouds may or may not be representative of the Milky Way circumgalactic medium as a whole.”