Significant luminosity evolution mimicking dark energy in supernova cosmology

Supernova (SN) cosmology is based on the assumption that the corrected luminosity of SN Ia would not evolve with redshift. Recently, age dating of early-type host galaxies (ETGs) from high-quality spectra has shown that this key assumption is most likely in serious error. It has been argued though that the age-Hubble residual (HR) correlation from ETGs is not confirmed from two independent age datasets measured from multi-band optical photometry of host galaxies of all morphological types. Here we show, however, that one of them is based on highly uncertain and inappropriate luminosity-weighted ages derived, in many cases, under serious template mismatch. The other dataset employs more reliable mass-weighted ages, but the statistical analysis involved is highly affected by “dilution bias”, severely underestimating both the slope and significance of the age-HR correlation. Surprisingly, when we apply regression analysis with a standard posterior sampling method to this dataset comprising a large sample of host galaxies, very significant (> 99.99%) correlation is obtained between the global population age and HR with the slope (-0.047 mag/Gyr) in excellent agreement with our previous spectroscopic result from ETGs. For the local age of the environment around the site of SN in a host galaxy, a similarly significant (> 99.96%) correlation is also obtained with an even steeper slope (-0.057 mag/Gyr) which is fully comparable to the observed dimming of SN with redshift. Therefore, the luminosity evolution stands up to scrutiny as a serious systematic bias that can mimic dark energy in SN cosmology.