SIMBAD references

We present the first large, blind and uniformly selected survey for molecular hydrogen (H2) in damped Lyman α systems (DLAs) with moderate-to-high resolution spectra. 86 DLAs were searched for absorption in the many Lyman and Werner H2 transitions, with ~79 per cent completeness for H2 column densities above N(H2) = 10^17.5/cm2 for an assumed Doppler broadening parameter b = 2 km/s. Only a single strong H2 absorber was found - a system detected previously in Very Large Telescope/Ultraviolet and Visual Echelle Spectrograph spectra. Given our distribution of N(H2) upper limits, this ∼ 1 per cent detection rate is smaller than expected from previous surveys at 99.8 per cent confidence. Assuming the N(H2) distribution shape from previous surveys, our detection rate implies a covering factor of ∼ 1 per cent for N(H2) ≥ 10^17.5/cm2 gas in DLAs (<6 per cent at 95 per cent confidence). We obtained new Magellan/Magellan Echellette (MagE) spectra for 53 DLAs; 8 km/s resolution spectra were available for 27 DLAs. MagE's moderate resolution (~71 km/s) yields weaker N(H2) upper limits and makes them dependent on the assumed Doppler parameter. For example, half the (relevant) previous H2 detections have N(H2) ≥ 10^18.1/cm2, a factor of just 3 higher than our median upper limit. Nevertheless, several tests suggest our upper limits are accurate, and they would need to be increased by 1.8 dex to bring our detection rate within 95 per cent confidence of previous surveys.