Active galactic nuclei through the prism of galaxy clusters: bounds on axion-like particles

TL;DR

This paper proposes a novel method of stacking spectra from active galactic nuclei behind galaxy clusters to detect axion-like particles, improving bounds on their properties and advancing dark matter research.

Contribution

It introduces a new stacking approach that averages magnetic field uncertainties, enabling exploration of previously inaccessible ALP parameter space with implications for dark matter detection.

Findings

Stacked spectra reveal step-like features indicative of photon-ALP conversion.

Method improves bounds on ALP properties across a wide mass range.

Future telescopes like CTA will enhance sensitivity to ALPs as dark matter candidates.

Abstract

Hypothetical axion-like particles (ALPs) are of interest because of their potential to act as dark matter or to reveal information about yet undiscovered fundamental constituents of matter. Such particles can be created when photons traverse regions of magnetic fields. The conversion probability depends on both the magnetic field parameters and photon energy, leading to multiple spectral absorption features as light passes through magnetized regions. Traditionally, astrophysical searches have focused on detecting such features in individual objects. However, the limited understanding of properties of cosmic magnetic fields have hindered the progress. Here we introduce a new approach by analyzing stacked (rather than individual) spectra of active galactic nuclei (AGNs) positioned behind galaxy clusters -- gigantic magnetic field reservoirs. Stacking efficiently averages over the uncertainties in magnetic fields, revealing a unique step-like spectral signature of photon-to-ALP conversion. With this approach we advance into previously inaccessible regions of the ALP parameter space for nano-electronvolt masses. Adopting this method will significantly improve existing bounds across a wide range of masses by using different telescopes and increasing the size of the stacked datasets. The Cherenkov Telescope Array Observatory, in particular, will extensively probe the parameter space where ALPs could serve as dark matter.