Speaker
Dr
Marc Rafelski
(IPAC (Caltech))
Description
We present chemical abundance measurements for damped Lyα systems (DLAs) at z>4, which show a clear decrease in the metallicity of DLAs with increasing redshift. We find a possible break in the metallicity evolution of DLAs at z>4.7, and showcase our latest results using new Keck ESI and Magellan FIRE spectra. This break may represent a transition in the nature of DLAs, where high redshift cold flows begin to host low HI column density and low metallicity DLAs. Even with the observed break, we show that the metallicity 'floor' of ~1/600 solar continues out to z~5, despite our sensitivity for finding DLAs with much lower metallicities. In addition, we find that the metallicity distribution and the α/Fe ratios of z>2 DLAs are consistent with those of halo stars. It is therefore possible that the halo stars in the Milky Way formed out of DLA gas.
