Spectrum of the Supernova Relic Neutrino Background and Metallicity Evolution of Galaxies

TL;DR

This paper models the supernova relic neutrino background considering black hole formation and galaxy metallicity evolution, highlighting how cosmic star formation influences the neutrino spectrum detectable by Super-Kamiokande.

Contribution

It provides the first quantitative estimate of failed supernovae's contribution to SRNs based on metallicity evolution and explores how various astrophysical parameters affect the SRN spectrum.

Findings

Low-energy SRN spectrum mainly depends on cosmic star formation rate.

Failed supernovae significantly contribute to the SRN background.

Detectable SRN signals are expected in Super-Kamiokande with gadolinium.

Abstract

The spectrum of the supernova relic neutrino (SRN) background from past stellar collapses including black hole formation (failed supernovae) is calculated. The redshift dependence of the black hole formation rate is considered on the basis of the metallicity evolution of galaxies. Assuming the mass and metallicity ranges of failed supernova progenitors, their contribution to SRNs is quantitatively estimated for the first time. Using this model, the dependences of SRNs on the cosmic star formation rate density, shock revival time and equation of state are investigated. The shock revival time is introduced as a parameter that should depend on the still unknown explosion mechanism of core collapse supernovae. The dependence on equation of state is considered for failed supernovae, whose collapse dynamics and neutrino emission are certainly affected. It is found that the low-energy spectrum of SRNs is mainly determined by the cosmic star formation rate density. These low-energy events will be observed in the Super-Kamiokande experiment with gadolinium-loaded water.