Measurement of the power spectrum turnover scale from the cross-correlation between CMB lensing and Quaia

TL;DR

This paper measures the large-scale turnover in the matter power spectrum using quasar and CMB lensing data, providing new constraints on cosmological parameters and the universe's expansion rate.

Contribution

It presents the first detection of the power spectrum turnover scale from cross-correlation data, offering an independent standard ruler for cosmology.

Findings

Turnover detected at 2.3-3.1 sigma significance.

Current expansion rate H0 measured as 62.7±17.2 km/s/Mpc.

Constraints on CMB temperature and relativistic species independent of CMB data.

Abstract

We use the projected clustering of quasars in the Gaia-unWISE quasar catalog, Quaia, and its cross-correlation with CMB lensing data from Planck, to measure the large-scale turnover of the matter power spectrum, associated with the size of the horizon at the epoch of matter-radiation equality. The turnover is detected with a significance of between $2.3$ and $3.1\sigma$, depending on the method used to quantify it. From this measurement, the equality scale is determined at the $\sim20\%$ level. Using the turnover scale as a standard ruler alone (suppressing information from the large-scale curvature of the power spectrum), in combination with supernova data through an inverse distance ladder approach, we measure the current expansion rate to be $H_0=62.7\pm17.2\,{\rm km}\,{\rm s}^{-1}\,{\rm Mpc}^{-1}$. The addition of information coming from the power spectrum curvature approximately halves the standard ruler uncertainty. Our measurement in combination with calibrated supernovae from Pantheon$+$ and SH0ES constrains the CMB temperature to be $T_{\rm CMB}=3.10^{+0.48}_{-0.36}\,{\rm K}$, independently of CMB data. Alternatively, assuming the value of $T_{\rm CMB}$ from COBE-FIRAS, we can constrain the effective number of relativistic species in the early Universe to be $N_{\rm eff}=3.0^{+5.8}_{-2.9}$.