State of the Universe

Evidence for strong progenitor age bias in supernova cosmology

by Dr. Young- Wook Lee (Yonsei University, Seoul)

Friday, December 9, 2022 from to (Asia/Kolkata)
at Zoom : Meeting ID: 825 1295 6967 Passcode: 384194
Supernova (SN) cosmology is based on the assumption that the width- luminosity relation (WLR) and the colour-luminosity relation (CLR) in the type Ia SN luminosity standardization would not show zero-point offsets with progenitor age. Unlike this expectation, recent age datings of stellar populations in host galaxies have shown significant correlations between progenitor age and Hubble residual (HR). Here we show that this correlation originates from a strong progenitor age dependence of the zero-points of the  WLR and CLR, in the sense that SNe from younger progenitors are fainter each at given light-curve parameters x1 and c. This 4.6 sigma result is reminiscent of Baade's discovery of the zero-point variation of the Cepheid period-luminosity relation with population age, and, as such, causes a serious systematic bias with redshift in SN cosmology. Other host properties show substantially smaller and insignificant offsets in the WLR and CLR for the same dataset. We illustrate that the differences between the high-z and low-z SNe in the WLR and CLR, and in HR after the standardization, are fully comparable to those between the correspondingly young and old SNe at intermediate redshift, indicating that the observed dimming of SNe with redshift may well be an artifact of over-correction in the luminosity standardization. When this systematic bias with redshift is properly taken into account, there is little evidence left for an accelerating universe, posing a serious question to one of the cornerstones of the concordance model.