The weakness of C IV absorber clustering in Keck HIRES spectra of adjacent quasar sight lines

We observe with Keek/HIRES the z approximate to 2.5 QSO triplet 1623+27 in order to explore on the scale of 1 Mpc the spatial clustering of C Iv absorbers between adjacent sight lines. We find this signal to be significantly weaker than the clustering in velocity on corresponding scales along single sight lines, assuming that the relative velocity of absorbers in dominated hv the Hubble flow Thin indicates that small-scale clustering (200 km s(-1) < Delta v < 600 km s(-1)) of the C Iv absorbers cannot be interpreted in terms of the positions of the absorbers in space but must be considered as internal motions within individual absorbers or within clusters of absorbers whose internal velocities dominate over Hubble expansion across the cluster scale. If the single sight line signal is due to spatial clustering, it is caused by absorber clusters smaller than would be implied by their velocities if a Hubble flow is assumed. The spatial clustering of C Iv absorbers at z approximate to 2 is consistent with data on Ly alpha forest clustering measured in the same way at the same redshifts. However, present-day galaxy clustering, evolved back to z approximate to 2, is consistent with C Iv spatial clustering but perhaps not with that of the Ly alpha forest. Even so, one cannot as yet distinguish the two absorber populations on the basis of spatial clustering on these small scales.