Observational Evidence for the Infall of Low-Metallicity Gas onto the Milky Way

We find evidence for a hitherto unknown component of the Milky Way: infalling gas with low heavy element abundances. Infall of metal-poor matter has been the preferred solution to the long-standing ``G-dwarf problem'', the fact that the abundance distribution of unevolved stars is narrower than expected in a simple model (e.g. Pagel 1997). Our conclusion is based on the metallicity we measure for the high-velocity cloud complex C of 0.070+/-0.020 times solar, using the Seyfert galaxy Mark 290 as a background probe. We also determine a lower limit of 5 kpc to its distance and argue that it is likely that D3 Gyr ago (Toomre, in Kerr & Sullivan 1969). This work was supported by NASA under grant #GO6590.01-95A