Local gravitational redshifts can bias cosmological measurements
  Measurements of cosmological parameters via the distance-redshift relation
usually rely on models that assume a homogenous universe. It is commonly
presumed that the large-scale structure evident in our Universe has a
negligible impact on the measurement if distances probed in observations are
sufficiently large (compared to the scale of inhomogeneities) and are averaged
over different directions on the sky. This presumption does not hold when
considering the effect of the gravitational redshift caused by our local
gravitational potential, which alters light coming from all distances and
directions in the same way. Despite its small magnitude, this local
gravitational redshift gives rise to noticeable effects in cosmological
inference using SN Ia data. Assuming conservative prior knowledge of the local
potential given by sampling a range of gravitational potentials at locations of
Milky-Way-like galaxies identified in cosmological simulations, we show that
ignoring the gravitational redshift effect in a standard data analysis leads to
an additional systematic error of ~1 per cent in the determination of density
parameters and the dark energy equation of state. We conclude that our local
gravitational field affects our cosmological inference at a level that is
important in future observations aiming to achieve percent-level accuracy.
