Molecular hydrogen in DLAs

Figure 5 in Noterdame et al (2008, arXiv:0801.3682)
Caption: The figure shows the fraction of molecular hydrogen found in z~2.5 DLAs as a function of metallicity. The filled symbols show actual detections and the open symbols upper limits. These results is from a large survey of existing UVES data on DLAs but the results do not appear to be strongly biased by the heterogeneous nature of the data. The dashed horizontal line shows their adopted completeness limit and the dashed vertical line where they split their sample into low and high metallicity systems.

What is intersting is a) that selecting high metallicity DLAs is an efficient way to find systems with molecular hydrogen and b) that molecular fractions appear to be very low in DLAs. Neither was unknown but this is the largest compilation thus far and allows other correlations to be studied.