Axion-Like Particle Dark Matter Intensity Mapping: A New Probe via Cross-Correlation with Galaxy Surveys

The particle nature of dark matter (DM) remains one of the most significant enigmas in modern cosmology. Axion-like particles (ALPs), as well-motivated candidates for cold dark matter, can undergo radiative decay into photon pairs, a process that is significantly enhanced in the presence of ambient radiation fields. In this work, we propose a novel probe of $\mu{\rm eV}$-scale ALP DM by cross-correlating radio intensity mapping (IM) with the large-scale galaxy distribution from the 2MASS Redshift Survey (2MRS) in the local universe ($z\leq 0.1$). We develop a comprehensive theoretical framework that incorporates stimulated decay effects driven by both the Cosmic Microwave Background (CMB) and a bottom-up modeled extragalactic radio background (ERB). By forecasting the sensitivity of the Square Kilometre Array (SKA) Phase 2, we demonstrate that this cross-correlation technique provides a promising and complementary approach to searching for ALP DM signals. This study establishes a new proof-of-concept for utilizing next-generation radio telescopes to probe ALP dark matter on cosmic scales.