Detection of cross-correlation between CMB Lensing and low-density points

Low Density Points (LDPs, citet{2019ApJ...874....7D}), obtained by removing high-density regions of observed galaxies, can trace the Large-Scale Structures (LSSs) of the universe. In particular, it offers an intriguing opportunity to detect weak gravitational lensing from low-density regions. In this work, we investigate tomographic cross-correlation between Planck CMB lensing maps and LDP-traced LSSs, where LDPs are constructed from the DR8 data release of the DESI legacy imaging survey, with about $10^6$-$10^7$ galaxies. We find that, due to the large sky coverage (20,000 deg$^2$) and large redshift depth ($zleq 1.2$), a significant detection ($10sigma$--$30sigma$) of the CMB lensing-LDP cross-correlation in all six redshift bins can be achieved, with a total significance of $sim 53sigma$ over $ ellle1024$. Moreover, the measurements are in good agreement with a theoretical template constructed from our numerical simulation in the WMAP 9-year $Lambda$CDM cosmology. A scaling factor for the lensing amplitude $A_{rm lens}$ is constrained to $A_{rm lens}=1pm0.12$ for $z<0.2$, $A_{rm lens}=1.07pm0.07$ for $0.2<z<0.4$ and $A_{rm lens}=1.07pm0.05$ for $0.4<z<0.6$, with the r-band absolute magnitude cut of $-21.5$ for LDP selection. A variety of tests have been performed to check the detection reliability, against variations in LDP samples and galaxy magnitude cuts, masks, CMB lensing maps, multipole $ell$ cuts, sky regions, and photo-z bias. We also perform a cross-correlation measurement between CMB lensing and galaxy number density, which is consistent with the CMB lensing-LDP cross-correlation. This work therefore further convincingly demonstrates that LDP is a competitive tracer of LSS.