We present a fully consistent catalog of local and global properties of host galaxies of 882 Type Ia supernovæ ( SNIa ) that were selected based on their light-curve properties , spanning the redshift range 0.01 < z < 1. \text { } This catalog corresponds to a preliminary version of the compilation sample and includes Supernova Legacy Survey ( SNLS ) 5-year data , Sloan Digital Sky Survey ( SDSS ) , and low-redshift surveys .
We measured low- and moderate-redshift host galaxy photometry in SDSS stacked and single-epoch images and used spectral energy distribution ( SED ) fitting techniques to derive host properties such as stellar mass and U - V rest-frame colors ; the latter are an indicator of the luminosity-weighted age of the stellar population in a galaxy .
We combined these results with high-redshift host photometry from the SNLS survey and thus obtained a consistent catalog of host stellar masses and colors across a wide redshift range .
We also estimated the local observed fluxes at the supernova location within a proper distance radius of 3 kpc , corresponding to the SNLS imaging resolution , and transposed them into local U - V rest-frame colors .
This is the first time that local environments surrounding SNIa have been measured at redshifts spanning the entire Hubble diagram .
Selecting SNIa based on host photometry quality , we then performed cosmological fits using local color as a third standardization variable , for which we split the sample at the median value .
We find a local color step significance of -0.091 \pm 0.013 mag ( 7 \sigma ) , which effect is as significant as the maximum mass step effect .
This indicates that the remaining luminosity variations in SNIa samples can be reduced with a third standardization variable that takes the environment into account .
Correcting for the maximum mass step correction of -0.094 \pm 0.013 mag , we find a local color effect of -0.057 \pm 0.012 mag ( 5 \sigma ) , which shows that additional information is provided by the close environment of SNIa .
Departures from the initial choices were investigated and showed that the local color effect is still present , although less pronounced .
We discuss the possible implications for cosmology and find that using the local color in place of the stellar mass results in a change in the measured value of the dark energy equation-of-state parameter of 0.6 % .
Standardization using local U - V color in addition to stretch and color reduces the total dispersion in the Hubble diagram from 0.15 to 0.14 mag .
This will be of tremendous importance for the forthcoming SNIa surveys , and in particular for the Large Synoptic Survey Telescope ( LSST ) , for which uncertainties on the dark energy equation of state will be comparable to the effects reported here .