The cosmic transparency measured with Type Ia supernovae: implications for intergalactic dust

TL;DR

This study uses Type Ia supernova observations to investigate cosmic transparency and intergalactic dust effects, suggesting that dust could account for observed dimming and emphasizing the importance of future measurements for accurate cosmology.

Contribution

It introduces a model linking supernova dimming to intergalactic dust density and discusses how future data can refine these measurements for cosmological insights.

Findings

Discrepancy in supernova distance moduli may be due to intergalactic dust.

Estimated cosmic dust density is $oxed{8 imes 10^{-5}}$ with redshift dependence.

Future supernova surveys can better constrain intergalactic dust properties.

Abstract

Observations of high-redshift Type Ia supernovae (SNe~Ia) are used to study the cosmic transparency at optical wavelengths. Assuming a flat $\Lambda$CDM cosmological model based on BAO and CMB results, redshift dependent deviations of SN~Ia distances are used to constrain mechanisms that would dim light. The analysis is based on the most recent Pantheon SN compilation, for which there is a $0.03\pm0.01 {\textrm \,(\rm stat)}$ mag discrepancy in the distant supernova distance moduli relative to the $\Lambda$CDM model anchored by supernovae at $z<0.05$. While there are known systematic uncertainties that combined could explain the observed offset, here we entertain the possibility that the discrepancy may instead be explained by scattering of supernova light in the intergalactic medium (IGM). We focus on two effects: Compton scattering by free electrons and extinction by dust in the IGM. We find that if the discrepancy is due entirely to dimming by dust, the measurements can be modeled with a cosmic dust density $\Omega_{\rm IGM}^{\rm dust} = 8 \cdot 10^{-5} (1+z)^{-1}$, corresponding to an average attenuation of $2\cdot 10^{-5}$ mag Mpc$^{-1}$ in V-band. Forthcoming SN~Ia studies may provide a definitive measurement of the IGM dust properties, while still providing an unbiased estimate of cosmological parameters by introducing additional parameters in the global fits to the observations.