Over-Luminous Type Ia Supernovae and Standard Candle Cosmology

TL;DR

The paper investigates the Hubble tension by focusing on over-luminous Type Ia supernovae, which challenge standardization schemes. It introduces a modified magnitude relation $M_B = a + b(\Delta m_{15} - c) + R(B-V)$ and applies Bayesian inference to a sample of 15 over-luminous SNe Ia to estimate $H_0$, reporting $H_0 \approx 73.60^{+10.14}_{-7.18}$ (flat prior) and $H_0 \approx 73.02^{+1.38}_{-1.40}$ (Cepheid prior), with sensitivity to $a$ and $b$. The work suggests that including these events could lower $H_0$ toward early-universe values, though results depend on assumptions about the absolute-magnitude calibration and the degree of standardization achievable for these objects. It emphasizes the need for larger samples and theoretical development of the Phillips relation for super-Chandrasekhar progenitors to determine whether over-luminous SNe Ia can be robustly used in distance measurements.

Abstract

Type Ia supernovae (SNe\,Ia) serve as crucial cosmological distance indicators because of their empirical consistency in peak luminosity and characteristic light curve decline rates. These properties facilitate them to be standardized candles for the determination of the Hubble constant ($H_0$) within late-time universe cosmology. Nevertheless, a statistically significant difference persists between $H_0$ values derived from early and late-time measurements, a phenomenon known as the Hubble tension. Furthermore, recent observations have identified a subset of over-luminous SNe\,Ia, characterized by peak luminosities exceeding the nominal range and faster decline rates. These discoveries raise questions regarding the reliability of SNe\,Ia as standard candles for measuring cosmological distances. In this article, we present the Bayesian analysis of 15 over-luminous SNe\,Ia and show that they yield a lower $H_0$ estimate due to the increase in their absolute magnitude. This investigation potentially represents a step toward addressing the Hubble tension.

Figures (2)

• Figure 1: Probability distributions of likelihood function with respect to $H_0$ along with the corresponding 1$\sigma$ confidence intervals for $a=-19.48$, $b=0.52$, and $c=1.05$. The green curve represents the case of a flat prior on $H_0$ that is maximized at $H_{0} = 73.60_{-7.18}^{+10.14} \rm \, km \, s^{-1} \, Mpc^{-1}$. Red curve represents the case for Gaussian prior on $H_0$ from Cepheid variable stars and maxima of the likelihood function shifts to $H_0 = 73.02_{-1.40}^{+1.38} \rm\,km\,s^{-1}\,Mpc^{-1}$.
• Figure 2: Maximized values of $H_0$ for different combinations of $a$ and $b$ in the case of a flat prior on $H_0$ for a fixed $c=0.84$.