Open AccessQuasar–galaxy associations revisited
Author(s) -
Benítez N.,
Sanz J. L.,
MartínezGonzález E.
Publication year - 2001
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2001.03936.x
Subject(s) - physics , quasar , astrophysics , galaxy , gravitational lens , qsos , astronomy , extinction (optical mineralogy) , weak gravitational lensing , redshift , optics
Gravitational lensing predicts an enhancement of the density of bright, distant quasi‐stellar objects (QSOs) around foreground galaxies. We measure this QSO–galaxy correlation w qg for two complete samples of radio‐loud quasars, the southern 1 Jy and half‐Jansky samples. The existence of a positive correlation between quasars and galaxies is confirmed at a per cent significance level (>99.9 per cent if previous measurements on the northern hemisphere are included). A comparison with the results obtained for incomplete quasar catalogues (e.g. the Veron‐Cetty and Veron compilation) suggests the existence of an ‘identification bias’, which spuriously increases the estimated amplitude of w qg for incomplete samples. This effect may explain many of the surprisingly strong quasar–galaxy associations found in the literature. Nevertheless, the value of w qg that we measure in our complete catalogues is still considerably higher than the predictions from weak lensing. We consider two effects which could help to explain this discrepancy: galactic dust extinction and strong lensing.