Galaxy clustering in the DESI Legacy Survey and its imprint on the CMB
  We use data from the DESI Legacy Survey imaging to probe the galaxy density
field in tomographic slices covering the redshift range $0<z<0.8$. After
careful consideration of completeness corrections and galactic cuts, we obtain
a sample of $4.9\times 10^7$ galaxies covering 17 739 deg$^2$. We derive
photometric redshifts with precision $\sigma_z/(1+z)=0.012 - 0.015$, and
compare with alternative estimates. Cross-correlation of the tomographic galaxy
maps with Planck maps of CMB temperature and lensing convergence probe the
growth of structure since $z=0.8$. The signals are compared with a fiducial
Planck $\Lambda$CDM model, and require an overall scaling in amplitude of
$A_\kappa=0.901\pm 0.026$ for the lensing cross-correlation and $A_{\rm ISW} =
0.984 \pm 0.349$ for the temperature cross-correlation, interpreted as the
Integrated Sachs-Wolfe effect. The ISW amplitude is consistent with the
fiducial $\Lambda$CDM prediction, but lies significantly below the prediction
of the AvERA model of R\'acz et al. (2017), which has been proposed as an
alternative explanation for cosmic acceleration. Within $\Lambda$CDM, our low
amplitude for the lensing cross-correlation requires a reduction either in
fluctuation normalization or in matter density compared to the Planck results,
so that $\Omega_m^{0.78}\sigma_8=0.297\pm 0.009$. In combination with the total
amplitude of CMB lensing, this favours a shift mainly in density:
$\Omega_m=0.274\pm0.024$. We discuss the consistency of this figure with
alternative evidence. A conservative compromise between lensing and primary CMB
constraints would require $\Omega_m=0.296\pm0.006$, where the 95% confidence
regions of both probes overlap.
