First detection of the Hubble variation correlation and its scale dependence

TL;DR

This paper uncovers a scale-dependent correlation between local Hubble constant variations and galaxy density contrasts, revealing potential unknown effects or new physics influencing cosmic expansion measurements.

Contribution

It introduces the first theoretical and observational analysis of the scale dependence of Hubble constant variations and their correlation with galaxy density contrasts.

Findings

Identified a residual linear correlation between local H_0 and galaxy density contrasts.

Traced the scale dependence of this correlation, increasing at larger scales.

Results are marginally consistent with the standard bc CDM model.

Abstract

The sample variance due to our local density fluctuations in measuring our local Hubble-constant ($H_0$) can be reduced to the percentage level by choosing the Hubble-flow type Ia supernovae (SNe Ia) outside of the homogeneity scale. In this Letter, we have revealed a hidden trend in this one-percent $H_0$ variation both theoretically and observationally. We have derived for the first time our $H_0$ variation measured from any discrete sample of distant SNe Ia. We have also identified a residual linear correlation between our local $H_0$ fitted from different groups of SNe Ia and their ambient density contrasts of SN-host galaxies evaluated at a given scale. We have further traced the scale dependence of this residual linear trend, which becomes more and more positively correlated with the ambient density contrasts of SN-host galaxies estimated at larger and larger scales, on the contrary to but still marginally consistent with the theoretical expectation from the $\Lambda$-cold-dark-matter model. This might indicate some unknown corrections to the peculiar velocity of the SN-host galaxy from the density contrasts at larger scales or the smoking gun for the new physics.