An aluminum-enhanced cloud in A C IV absorber at z = 1.94

In the z = 1.94 C Iv absorption-line system in the spectrum of quasar Q1222+228 (z(em) = 2.04), we find two clouds that have contrasting physical conditions, although they are only at a 17 km s(-1) velocity separation. In the first cloud, Si Ii, Si Iv, and C Ir are detected, and Al Ii and Al III column density limits in conjunction with photoionization models allow us to infer that this cloud has a large Si abundance and a small Al abundance relative to a solar abundance pattern. This pattern resembles that of Galactic metal-poor halo stars, which must have formed from such high-redshift gas. The second cloud, in contrast, has detected Al II and Al III (also Si Iv and C Ir) but no detected Si II. We demonstrate, using photoionization models, that Al/Si must be greater than (Al/Si). in this unusual cloud. Such a ratio is not found in absorption profiles looking through Milky Way gas. It cannot be explained by dust depletion since Al depletes more severely than Si. Comparing this cloud with other Al-rich environments, we speculate about the processes and conditions that could give rise to this abundance pattern.