Testing $\Lambda$CDM at the lowest redshifts with SN Ia and galaxy velocities

TL;DR

This study tests the $ ext{Lambda}$CDM cosmological model at very low redshifts by analyzing peculiar velocities from supernovae and galaxy data, confirming the model's predictions with high significance.

Contribution

It introduces a combined analysis of SN Ia and galaxy velocities using new calibrations, providing precise constraints on the velocity signal amplitude and growth rate at low redshift.

Findings

Consistent with $ ext{Lambda}$CDM predictions at >7σ and >8σ significance.

Constrains the signal amplitude to $A=1.05_{-0.21}^{+0.25}$, close to the fiducial model.

Measures $f \sigma_8=0.428_{-0.045}^{+0.048}$ at $z_{eff}=0.02$.

Abstract

Peculiar velocities of objects in the nearby universe are correlated due to the gravitational pull of large-scale structure. By measuring these velocities, we have a unique opportunity to test the cosmological model at the lowest redshifts. We perform this test, using current data to constrain the amplitude of the "signal" covariance matrix describing the velocities and their correlations. We consider a new, well-calibrated "Supercal" set of low-redshift SNe Ia as well as a set of distances derived from the fundamental plane relation of 6dFGS galaxies. Analyzing the SN and galaxy data separately, both results are consistent with the peculiar velocity signal of our fiducial $\Lambda$CDM model, ruling out the noise-only model with zero peculiar velocities at greater than $7\sigma$ (SNe) and $8\sigma$ (galaxies). When the two data sets are combined appropriately, the precision of the test increases slightly, resulting in a constraint on the signal amplitude of $A = 1.05_{-0.21}^{+0.25}$, where $A = 1$ corresponds to our fiducial model. Equivalently, we report an 11% measurement of the product of the growth rate and amplitude of mass fluctuations evaluated at $z_\text{eff} = 0.02$, $f \sigma_8 = 0.428_{-0.045}^{+0.048}$, valid for our fiducial $\Lambda$CDM model. We explore the robustness of the results to a number of conceivable variations in the analysis and find that individual variations shift the preferred signal amplitude by less than ${\sim}0.5\sigma$. We briefly discuss our Supercal SN Ia results in comparison with our previous results using the JLA compilation.