unWISE tomography of Planck CMB lensing
  CMB lensing tomography, or the cross-correlation between CMB lensing maps and
large-scale structure tracers over a well-defined redshift range, has the
potential to map the amplitude and growth of structure over cosmic time,
provide some of the most stringent tests of gravity, and break important
degeneracies between cosmological parameters. In this work, we use the unWISE
galaxy catalog to provide three samples at median redshifts $z \sim 0.6, 1.1$
and 1.5, fully spanning the Dark Energy dominated era, together with the most
recent Planck CMB lensing maps. We obtain a combined cross-correlation
significance $S/N = 79.3$ over the range of scales $100 < \ell < 1000$. We
measure the redshift distribution of unWISE sources by a combination of
cross-matching with the COSMOS photometric catalog and cross-correlation with
BOSS galaxies and quasars and eBOSS quasars. We also show that magnification
bias must be included in our analysis and perform a number of null tests. In a
companion paper, we explore the derived cosmological parameters by modeling the
non-linearities and propagating the redshift distribution uncertainties.
