Detection of Weak Gravitational Lensing Magnification from Galaxy-qso Cross-correlation in the Sdss

We report a detection of galaxy-QSO cross-correlation wGQ in the Sloan Digital Sky Survey (SDSS) Early Data Release (EDR) over 0.2−30 arc-minute scales. We cross-correlate galaxy samples of different mean depths r = 19 − 22 (zG = 0.15 − 0.35) with the main QSO population (i′Q < 19.2) at zQ ≃ 1.6. We find positive detection in most cases (except for the faintest QSOs, as expected) with up to 8-sigma significance. The amplitude of the signal on arc-minute scales is about 20% at zG = 0.15 decreasing to 10% at zG = 0.35 This is a few times larger than currently expected from structure formation ΛCDM models on arc-minute scales, but confirms, at a higher significance, previous measurements by several groups. The shape and redshift evolution of wGQ agrees well with being a lensing signal. When compared to the galaxy-galaxy correlation wGG, this results indicate very strong and steep non-linear amplitude for the underlaying matter fluctuations: σ ≃ 400 on scales of 0.2 Mpc/h, in contradiction with non-linear modeling of ΛCDM fluctuations. We find a 3-sigma detection for the normalized skewness (galaxygalaxy-QSO correlation): S3 ≃ 18.6± 5.7. All these observational trends can be reconciled with flat Λ models with σ8 = 1, provided the linear spectrum is steeper (n ≃ 0.9) than in the ΛCDM model on small (cluster) scales. In the halo model this means steeper profiles. The galaxy distribution roughly traces this matter variance but with an amplitude that is 100 times smaller: ie galaxies are anti-bias with b ≃ 0.1 on these small scales. The bias is shown to increase with scale, which extrapolates well to b ≃ 1 at ≃ 10 Mpc/h. Subject headings: galaxies: clustering, large-scale structure of universe, cosmology