Title:  Evidence for a decelerating cosmic expansion from supernova cosmology

Date & Time: Friday, September 4th, 2020, 11:00 AM

Location: Online

( https://zoom.us/j/6210767044?pwd=SkRuRzZtbjcwQkszS2g4QThiWVl3dz09 , It will open at 10:30 AM)

Language: Korean

Speaker: Young-Wook Lee (Yonsei University)

Abstract

Supernova (SN) cosmology is based on the assumption that the corrected luminosity of SN Ia would not evolve with redshift. Recently, our age dating of early-type host galaxies (ETGs) from high-quality spectra has shown that this key assumption is most likely in error. It has been argued though that the age-Hubble residual (HR) correlation from ETGs is not confirmed from the age datasets measured from multi-band optical photometry of host galaxies of all morphological types. We find, however, that the statistical analysis involved is affected by "regression dilution bias", severely underestimating both the slope and significance of the age-HR correlation. Remarkably, when we apply regression analysis with a standard posterior sampling method to this dataset comprising a large sample of host galaxies, very significant (4.3 sigma) correlation is obtained between the population age and HR with the slope highly consistent with our previous spectroscopic result from ETGs. We also show that the light curve parameters (x1 & c) of high-z SNe are consistent with those of younger progenitors in the local universe. The corresponding luminosity evolution is significant enough to fully explain the observed dimming of SN with redshift without the dark energy. When the luminosity evolution is properly taken into account, SN data now strongly support a decelerating cosmic expansion! Since the SN cosmology has long been considered as the most direct evidence for the accelerating universe, an important avenue of future investigations would be to see how this new result from SNe can be reconciled with other cosmological probes.