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Paper: The Metallicity of HVC Complex C: Observational Evidence for the Accretion of Low-Metallicity Gas onto the Milky Way
Volume: 165, The Third Stromlo Symposium: The Galactic Halo
Page: 464
Authors: Wakker, Bart P.; Howk, J. Chris; Savage, Blair D.; Tufte, Steve L.; Reynolds, Ron J.; van Woerden, Hugo; Schwarz, Ulrich J.
Abstract: We present observations of the (field of the) Seyfert galaxy Mark 290, which probes the high-velocity cloud (HVC) complex C, one of the largest HVCs (Wakker & van Woerden 1991). We find that this object has a metallicity of 0.094+/-0.020^{+0.022}_{-0.019} times solar. A semi-theoretical upper limit of 30 kpc is set to its distance; D. Combined with the observed lower limit of 5 kpc (van Woerden et al. 1998b) this puts complex C in the galactic halo (z=3.5-20 kpc). The total gaseous mass is 2.0 tdex6 (D/5 kpc)^2 M_odot and, depending on whether the space velocity is completely radial or completely vertical, the HVC represents a downward mass flux of 0.036-0.083 (D/5 kpc) M_odot yr^{-1}, or 2.9-6.7 tdex{-3} (D/5 kpc)^{-1} M_odot yr^{-1} kpc^{-2}. These numbers suggest that complex C is unlikely to be part of a Galactic Fountain, but rather represents accreting low-metallicity material. Our results provide the first direct observational evidence for the infall of low-metallicity gas on the Milky Way, required in models of galactic chemical evolution.
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