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 halos and large-scale structure. The measurement is based on correlating the brightness of ∼85,000 quasars at z > 1 with the position of 20 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 ∼ θ , a distribution similar to mass. The amount of dust in galactic halos is found to be comparable to that in disks. On large scales its wavelength dependence is described by RV ≃ 3.9± 2.6, consistent with interstellar dust. We estimate the resulting opacity of the Universe as a function of redshift and find 〈AV 〉 ∼ 0.03 mag up to z = 0.5. This, in turn, implies a cosmic dust density of Ωdust ≃ 5× 10 , roughly half of which comes from dust in halos of ∼ L galaxies. We present magnification measurements, corrected for dust extinction, from which the galaxy-mass correlation function is inferred. The mean mass profile around galaxies is found to be Σ ∼ 30 (θ/1) hM⊙ pc −2 up to a radius of 10 Mpc, in agreement with gravitational shear estimates.