The Metallicity of HVC Complex C: Observational Evidence for the Accretion of Low-Metallicity Gas onto the Milky Way

Bart P. Wakker, J. Chris Howk, Blair D. Savage, Steve L. Tufte, Ron J. Reynolds, Hugo van Woerden, Ulrich J. Schwarz

    Research output: Chapter in Book/Report/Conference proceedingConference contributionAcademicpeer-review


    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.
    Original languageEnglish
    Title of host publicationThe third Stromlo symposium
    Subtitle of host publication the Galactic Halo : proceedings of a symposium held at Australian Academy of Science, Canberra, Australia, 17-21 August 1998
    Place of PublicationSan Francisco
    PublisherAstronomical Society of the Pacific
    ISBN (Print)1-886733-86-4
    Publication statusPublished - 1999

    Publication series

    Name Astronomical Society of the Pacific conference series

    Cite this