The Atacama Cosmology Telescope: High-redshift measurement of structure growth from the cross-correlation of Quaia quasars and CMB lensing from ACT DR6 and $\text{Planck}$ PR4

Abstract

We measure the amplitude of matter fluctuations over a wide range of redshifts by combining CMB lensing observations from ACT DR6 and $\text{Planck}$ PR4 with the overdensity of quasars from Quaia, a $\text{Gaia}$ and $\text{unWISE}$ quasar catalog. Our analysis includes the CMB lensing power spectrum from ACT DR6, the auto-correlation of two Quaia quasar samples centered at $z\simeq 1.0$ and $z\simeq 2.1$, and their cross-correlations with CMB lensing from both ACT DR6 and $\text{Planck}$ PR4. By performing a series of contamination and systematic null tests, we find no evidence for contamination in the lensing maps, contrary to what was suggested in previous Quaia cross-correlation analyses using $\text{Planck}$ PR4 CMB lensing data. From the joint analysis of the quasar auto- and cross-correlations with CMB lensing, and including BOSS BAO data to break the degeneracy between $\hat{I}{\text{c◯}}_m$ and $\ddot{I}{ƒ}_8$, we obtain $\ddot{I}{ƒ}_8=0.802_{-0.057}^{+0.045}$, consistent with $\hat{I}›$CDM predictions from $\text{Planck}$ primary CMB measurements. Combining the CMB lensing auto-spectrum with the cross-correlation measurement improves the constraint on $\ddot{I}{ƒ}_8$ by $12\%$ relative to the lensing auto-spectrum alone, yielding $\ddot{I}{ƒ}_8=0.804\pm 0.013$. This dataset combination also enables a reconstruction of structure growth across redshifts. We infer a $12\%$ constraint on the amplitude of matter fluctuations at $z>3$, with a measurement at the median redshift of the signal of $\ddot{I}{ƒ}_8(\tilde{z}=5.1)=0.146_{-0.014}^{+0.021}$, consistent with $\text{Planck}$ at the $1.4\ddot{I}ƒ$ level. These results provide one of the highest redshift constraints on the growth of structure to date.

30 pages, 15 figures, to be submitted to JCAP