High-energy neutrinos from FR0 radio-galaxies?

TL;DR

This paper investigates whether FR0 radio galaxies, the most common radio-loud AGN, could be sources of high-energy neutrinos by exploring their potential for proton-proton interactions in their host galaxies.

Contribution

It proposes a novel scenario where FR0 galaxies produce neutrinos through proton-proton interactions in their host galaxies, contrasting with the less efficient proton-photon mechanisms in jets.

Findings

FR0 galaxies are plausible neutrino sources via proton-proton interactions.

The proposed mechanism aligns with the population of faint, numerous sources.

Modeling supports the feasibility of neutrino production in FR0 host galaxies.

Abstract

The sources responsible for the emission of high-energy ($\gtrsim$ 100 TeV) neutrinos detected by IceCube are still unknown. Among the possible candidates, active galactic nuclei with relativistic jets are often examined, since the outflowing plasma seems to offer the ideal environment to accelerate the required parent high-energy cosmic rays. The non-detection of single point sources or -- almost equivalently -- the absence, in the IceCube events, of multiplets originating from the same sky position, constrains the cosmic density and the neutrino output of these sources, pointing to a numerous population of faint sources. Here we explore the possibility that FR0 radiogalaxies, the population of compact sources recently identified in large radio and optical surveys and representing the bulk of radio-loud AGN population, can represent suitable candidates for neutrino emission. Modeling the spectral energy distribution of a FR0 radiogalaxy recently associated to a $\gamma$-ray source detected by the Large Area Telescope onboard Fermi, we derive the physical parameters of its jet, in particular the power carried by it. We consider the possible mechanisms of neutrino production, concluding that $p\gamma$ reactions in the jet between protons and ambient radiation is too inefficient to sustain the required output. We propose an alternative scenario, in which protons, accelerated in the jet, escape from it and diffuse in the host galaxy, producing neutrinos as a result of $pp$ scattering with the interstellar gas, in strict analogy with the processes taking place in star-forming galaxies.