We present seven new abundance measurements of the elements O , C and Si at z > 4.5 , doubling the existing sample of weakly depleted elements in gas-rich galaxies , in order to constrain the first \sim 1 billion years of cosmic metal evolution .
These measurements are based on quasar spectra of damped Lyman-alpha absorbers ( DLAs ) and sub-DLAs obtained with the Magellan Inamori Kyocera Echelle ( MIKE ) and Magellan Echellette ( MagE ) spectrographs on Magellan-South , and the X-Shooter spectrograph on the Very Large Telescope .
We combine these new measurements with those drawn from the literature to estimate the N _ { H I } -weighted binned mean metallicity of -1.51 \pm 0.18 at z = 4.8 .
This metallicity value is in excellent agreement with the prediction from lower redshift DLAs , supporting the interpretation that the metallicity evolution is smooth at z \sim 5 , rather than showing a sudden decline at z > 4.7 .
Furthermore , the metallicity evolution trends for the DLAs and sub-DLAs are similar within our uncertainties .
We also find that the [ C/O ] ratios for z \sim 5 DLAs are consistent with those of the very metal-poor DLAs .
Additionally , using [ C/O ] and [ Si/O ] to constrain the nucleosynthesis models , we estimate that the probability distributions of the progenitor star masses for three relatively metal-poor DLAs are centered around 12 M _ { \odot } to 17 M _ { \odot } .
Finally , the z \sim 5 absorbers show a different metallicity-velocity dispersion relation than lower redshift DLAs , suggesting that they may be tracing a different population of galaxies .