科研之友
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摘要
The gas-phase and stellar metallicities have proven to be important parameters to constrain the star formation history of galaxies. However, H ii regions associated with recent star formation may not have abundances typical for the galaxy as a whole and it is believed that the bulk of the metals may be contained in the neutral gas. It is therefore important to directly probe the metal abundances in the neutral gas, which can be done by using absorption lines imprinted on a background quasar. Recently, we have presented studies of the stellar content of a small sample of such quasar absorbers with H i column densities measured to be in the sub-Damped Lyman alpha to Damped Lyman alpha range. Here, we present observations covering 300 nm to 2.5 mu m of emission line spectra of three of these absorbing-galaxies using the long-slit spectrograph X-Shooter on the Very Large Telescope. This allows us to compare the neutral and ionized-phase metallicities in the same objects and relates these measures to possible signature of low-metallicity gas accretion or outflows of gas enriched by star formation. Our results suggest that the abundances derived in absorption along the line of sight to background quasars are reliable measures of the overall galaxy metallicities. In addition to a comparison of abundances in different phases of the gas, a potential observational consequence of differences in fuelling mechanisms for disc galaxies is the internal distribution of their chemical abundances. We present some evidence for small negative metallicity gradients in the three systems. The flat slopes are in line with the differences observed between the two phases of the gas. These results suggest that a comparison of the H i and H ii metallicities is a robust indicator of abundance gradients in high-redshift galaxies and do not favour the presence of infall of fresh gas in these objects.
- 出版日期2014-2
