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 ~85000 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: Σ_dust ~ r^-0.8_p, a distribution similar to mass. On large scales, its wavelength dependence is described by R_V ~= 4.9 +/- 3.2, consistent with interstellar dust. This, in turn, implies a cosmic dust density of Ω_dust ~= 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 <A_V > ~ 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_solar pc^-2 up to a radius of 10 Mpc, in agreement with gravitational shear estimates.