DustER: Dust Extinction with Photometric Red Galaxies

We present DustER, a new method for reconstructing dust reddening maps from photometric galaxy survey data. DustER uses red galaxies as "standard crayons". That is, it relies on the mean color of red-sequence galaxies being independent of their position in the sky. Given the galaxy's redshift, the difference between a galaxy's observed color and its expected color measures the reddening by dust along the galaxy's line of sight. When using photometric galaxy survey data, the method must rely on photometric redshifts, which, combined with selection effects, bias the recovered dust maps. DustER uses a novel approach to characterize and correct for these biases by leveraging the known statistical properties of the distribution of dust around the Milky Way. Testing on simulations, we find that the recovered dust maps are contaminated by large-scale structure. However, when we use the DustER map to deredden and select red-sequence galaxies, we find the resulting two-point function is not contaminated by dust.