Revisiting the cosmological bias due to local gravitational redshifts

Abstract

A recent article by Wojtak et al. pointed out that the local gravitational redshift, despite its smallness (∼10^-5 ), can have a noticeable (∼1 %) systematic effect on our cosmological parameter measurements. The authors studied a few extended cosmological models (nonflat Λ CDM , w CDM , and w₀-w_aCDM ) with a mock supernova data set. We repeat this calculation and find that the ∼1 % biases are due to strong degeneracy between cosmological parameters. When cosmic microwave background (CMB) data are added to break the degeneracy, the biases due to local gravitational redshift are negligible (≲0.1 σ ).