Measuring the galaxy-mass and galaxy-dust correlations through magnification and reddening

We present a simultaneous detection of gravitational magnification and dust reddening effects due to galactic haloes and large-scale structure. The measurement is based on correlating the brightness of ∼85 000 quasars at z > 1 with the position of 24 million galaxies at z∼ 0.3 derived from the Sloan Digital Sky Survey and is used to constrain the galaxy–mass and galaxy–dust correlation functions up to cosmological scales. The presence of dust is detected from 20 kpc to several Mpc, and we find its projected density to follow: Σdust∼r−0.8p, a distribution similar to mass. On large scales, its wavelength dependence is described by RV≃ 4.9 ± 3.2, consistent with interstellar dust. This, in turn, implies a cosmic dust density of Ωdust≃ 5 × 10−6, roughly half of which comes from dust in haloes of ∼L★ galaxies. We estimate the resulting opacity of the Universe for various evolutionary models and find 〈AV〉∼ 0.03 mag up to z= 0.5. We present magnification measurements, corrected for dust extinction, from which the galaxy–mass correlation function is inferred to give the mean surface mass density profile around galaxies Σ∼ 30(θ/1 arcmin)−0.8h M⊙ pc−2 up to a radius of 10 Mpc, in agreement with gravitational shear estimates.