Detection of diffuse interstellar bands in the z=0.5 damped Lyα system toward AO 0235+164

We report the first detection of the 5705 and 5780 diffuse interstellar bands ( DIBs) in a moderate-redshift damped Ly alpha (DLA) system. We measure a rest- frame equivalent width of 63.2 +/- 8.7 m angstrom for the 5705 angstrom feature and 216 +/- 9 m for the 5780 angstrom feature in the z(abs) = 0.524 DLA toward AO 0235+164 and derive limits for the equivalent widths of the bands at 5797, 6284, and 6613 angstrom. The equivalent width of the 5780 angstrom band is lower than would be expected based on the Galactic correlation of DIB strength with N(H I) but is in good agreement with the correlation with E(B - V). The relative strengths of the 5780 and 6284 angstrom DIBs are inconsistent with all Galactic and extragalactic sight lines, except one Small Magellanic Cloud wing sight line toward Sk 143. However, the relative strengths of the 5705 and 5780 DIBs are consistent with the Galactic relation, indicating that the relative strengths of these bands may be less sensitive to environment or that they may be associated with a similar carrier. The detection of DIBs at z similar to 0.5 demonstrates that the organic compounds usually assumed to be the band carriers were already present in the universe some 5 Gyr ago.