The VST ATLAS Survey IV: Galaxy, LRG and QSO bias and HODs via ACT CMB Lensing
We present angular correlation and power spectral analyses of the clustering of VST ATLAS galaxies, LRGs and QSOs and their cross-correlations with the ACT DR6 CMB lensing map with its $\approx3\times$ higher resolution than Planck DR3. We first use $\Lambda$CDM Halofit models at linear scales to estimate galaxy, LRG and QSO bias, $b$, from the ratio of the 3-D power spectra, $b= P_{gg}/P_{gK}$ and hence the mass clustering amplitudes, $\sigma_8$. For galaxies we find $b_G(z=0.15)=1.22\pm0.07$, $\sigma_8(z=0)=0.71\pm0.06$ and for LRGs $b_{LRG}(z=0.26)=2.76\pm0.11$, $\sigma_8(z=0)=0.63\pm0.15$, both consistent with $\Lambda$CDM predictions. But for QSOs, we estimate a bias of $b_Q(z=1.7)=4.44\pm0.24$ and $\sigma_8(z=0)=0.49\pm0.06$, the latter significantly lower than expected for $\Lambda$CDM and leads to an observed $0.15<z<1.7$ gravitational growth rate faster than predicted for $\Lambda$CDM. At smaller non-linear scales, HOD model fits imply a broad halo mass distribution for $z\approx0.15$ galaxies but much narrower mass distributions for LRGs and QSOs. More surprisingly, the HOD fit for QSOs implies $M_{eff}=5\times10^{14}M_\odot$, $\approx10\times$ higher than expected. Finally, while the LRG and QSO HOD models fit $w_{gg}$ and $w_{gK}$ consistently, the same is not true for the $z\approx0.15$ galaxies unless we hypothesise anti-bias with $b_G\approx0.55$. This result supports previous QSO lensing analyses that also found anti-bias at $r<5$h$^{-1}$Mpc. We suggest that while HOD + NFW halo models may well describe LRG mass profiles and clustering, at intermediate scales the dominant galaxy population (and QSOs) may follow the alternative hierarchical clustering model of Peebles(1974) where galaxies trace the mass more closely than in a halo model.