Galaxy‐Quasar Correlations between APM Galaxies and Hamburg‐ESO QSOs

We detect angular galaxy-QSO cross-correlations between the APM GalaxyCatalogue and a preliminary release (consisting of roughly half of theanticipated final catalogue) of the Hamburg-ESO Catalogue of Bright QSOs as afunction of source QSO redshift using multiple cross-correlation estimators.Each of the estimators yield very similar results, implying that the APMcatalogue and the Hamburg-ESO survey are both fair samples of the respectivetrue galaxy and QSO populations. Though the signal matches the expectations ofgravitational lensing qualitatively, the strength of the measuredcross-correlation signal is significantly greater than the CDM models oflensing by large scale structure would suggest. This same disagreement betweenmodels and observation has been found in several earlier studies. We estimateour confidence in the correlation detections versus redshift by generating 1000random realizations of the Hamburg-ESO QSO survey: We detect physicalassociations between galaxies and low-redshift QSOs at 99% confidence anddetect lensing associations at roughly 95% confidence for QSOs with redshiftsbetween 0.6 and 1. Control cross-correlations between Galactic stars and QSOsshow no signal. Finally, the overdensities (underdensities) of galaxies nearQSO positions relative to those lying roughly 135 - 150 arcmin away areuncorrelated with differences in Galactic extinction between the two regions,implying that Galactic dust is not significantly affecting the QSO sample.Comment: 35 pages total, including 9 figures. Accepted by the Astrophysical Journa