Paper detail

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: Sigma_dust ~ theta^-0.8, 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 R_V=3.9+/-2.6, consistent with interstellar dust. We estimate the resulting opacity of the Universe as a function of redshift and find A_V~0.03 mag up to z=0.5. This, in turn, implies a cosmic dust density of Omega_dust ~ 5x10^-6, 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 Sigma ~ 30 (theta/arcmin)^-0.8 h M_sun/pc^2 up to a radius of 10 Mpc, in agreement with gravitational shear estimates.