Herbert-Fort et al. (2006) have recently identified a sample of 'metal-strong' absorbers from the SDSS, characterised by strong heavy-element absorption that is clearly detected even in low-resolution SDSS spectra. These metal-strong DLAs comprise ~5% of the total population. In some cases, the very strong metal lines are a symptom of high N(H i). In other cases, the metallicity is truly high compared with those of known DLAs. Although they are relatively rare, the statistical power of Sloan is expected to reveal several hundred metal-strong DLAs. Follow-up observations with high-resolution spectrographs will yield data for a myriad of applications, including the search for rarely detected atomic transitions, work on molecular species and the study of isotopic ratios.
In closing, it is interesting to note that, although the definition of 'metal-rich' at this conference has been somewhat subjective, with the exception of AGN (see e.g. Chapter 20 in these proceedings) we rarely find metallicities above 2ZQ in individual stars, H ii regions or galaxies. However, a handful of very supersolar abundances (up to 5 Z0) have recently been reported for QSO absorbers just below the traditional DLA column-density criterion of N(H i) > 2 x 1020 cm-2 (Peroux et al. 2006; Prochaska et al. 2006). The surprisingly high metallicities in these absorbers lead to a volley of new questions. How have these absorbers become so metal-rich at early times? What are their low-redshift analogues? What is the implication for the cosmic metals budget?
Was this article helpful?