We describe a tomographic dissection of the Planck CMB lensing data , cross-correlating this map with galaxies in different ranges of photometric redshift .
We use the nearly all-sky 2MPZ and WISE \times SCOS catalogues for z < 0.35 , extending to z < 0.6 using SDSS .
We describe checks for consistency between the different datasets , and perform a test for possible leakage of thermal Sunyaev–Zel ’ dovich signal into our cross-correlation measurements .
The amplitude of the cross-correlation allows us to estimate the evolution of density fluctuations as a function of redshift , thus providing a test of theories of modified gravity .
Assuming the common parametrisation for the logarithmic growth rate , f _ { g } = \Omega _ { m } ( z ) ^ { \gamma } , we infer \gamma = 0.77 \pm 0.18 when \Omega _ { m } is fixed using external data .
Thus CMB lensing tomography is currently consistent with Einstein gravity , where \gamma = 0.55 is expected .
We discuss how such constraints may be expected to improve with future data .