Little Red Dots as Hidden Neutrino Sources

TL;DR

Little Red Dots are high-redshift, compact galaxies with active black holes that could significantly contribute to the diffuse neutrino background, acting as hidden sources detectable through neutrino observations.

Contribution

This work introduces a new model linking high-redshift red galaxies with neutrino production via black hole activity and dense gaseous envelopes, explaining their potential role in the neutrino background.

Findings

LRDs can contribute up to 30% of the diffuse neutrino background at TeV–sub-PeV energies.

Neutrino flavor ratios are affected by muon cooling at high energies, offering a diagnostic for future telescopes.

LRDs are effective hidden sources due to their black hole and envelope configuration.

Abstract

Little Red Dots (LRDs) are enigmatic, compact, red galaxies at high redshift, $z\sim 4$-$7$, discovered by the James Webb Space Telescope. Broad emission lines in the absence of X-ray and radio counterparts suggest that they host accreting supermassive black holes embedded in dense gaseous envelopes. This black-hole-envelope configuration facilitates efficient photohadronic interactions and neutrino production. Remarkably, their observed source number density and luminosity are compatible with the energetics of the diffuse neutrino background. We consider that relativistic jets and outflows are launched from the black hole and propagate through low-density polar funnels within envelopes, where particle acceleration and neutrino emission occur. This leads to LRDs being effectively hidden sources. Our analytic and numerical calculations show that, in an optimistic scenario, LRDs can contribute $\sim 30\%$ of the observed diffuse background at TeV$-$sub-PeV energies, predominantly through photomeson production. At high neutrino energies, $\gtrsim 10^{5.5}~{\rm GeV}$, inverse-Compton cooling of muons modifies the resulting flavor ratio, providing a distinctive diagnostic for IceCube-Gen2 and other upcoming neutrino telescopes.