REANALYSIS OF THE ASSOCIATION OF HIGH-REDSHIFT 1-JANSKY QUASARS WITH IRAS GALAXIES

We develop a new statistical method to reanalyse angular correlations between background QSOs and foreground galaxies that are supposed to b e a consequence of dark matter inhomogeneities acting as weak gravitat ional lenses. The method is based on a weighted average over the galax y positions and is optimized to distinguish between a random distribut ion of galaxies around QSOs and a distribution which follows an assume d QSO-galaxy two-point correlation function, by choosing an appropriat e weight function. With simulations we demonstrate that this weighted average is slightly more sensitive than Spearman's rank-order test whi ch was used in previous investigations. In particular, the advantages of the weighted average show up if the correlation is weak. We then re analyze the correlation between high-redshift 1-Jansky QSOs and IRAS g alaxies taken from the IRAS Faint Source Catalog; these samples were a nalyzed previously using Spearman's rank-order test. In agreement with the previous work, we find moderate to strong correlations between th ese two samples; considering the angular two-point correlation functio n of these samples, we find a typical scale of order 5' from which mos t of the correlation signal derives. However, the statistical signific ance of the correlation changes with the redshift slices of the QSO sa mple one considers. Comparing with simple theoretical estimates of the expected correlation, we find that the signal we derive is considerab ly stronger than expected. On the other hand, recent direct verificati ons of the overdensity of matter in the line-of-sight to high-redshift radio QSOs obtained from the shear field around these sources indicat e that the observed association can be attributed to a gravitational l ens effect.