Abstract

The measurement of distance has long been a fundamental challenge in astrophysics. We have developed a method of inferring distances to astrophysical sources using spatial cross-correlations with galaxies of known redshift. These “clustering redshifts” are robust to problems plaguing other distance estimates and require only knowledge of the on-sky position of the sources. We have verified the method with sources with spectroscopic redshifts, demonstrating accuracies exceeding those required for many cosmological probes. Using this technique, we have explored the SDSS photometric galaxies, characterizing their distances and discovering entirely unidentified populations within. Clustering redshifts are proving their potential in the era of large scale surveys, such as LSST and DES, and will be a new tool in unlocking the third dimension of astronomical observations from the radio to the X-ray.