Speaker
Description
Understanding how active galactic nuclei (AGN) evolve with cosmic time and interact with their host galaxies is central to constraining the role of AGN feedback in galaxy evolution. In the era of deep, wide-field sky surveys, it is now possible to statistically characterise the relationship between radio AGN activity and host galaxy properties across the full AGN population. We investigate the fraction of radio-loud AGN as a function of redshift and stellar mass by combining observations from LOFAR with data from the Euclid space telescope. Previous research on radio sources in the local universe (z < 0.3) has identified a clear and steep power-law dependence of the radio-loud AGN fraction on the stellar mass. Using new data in the Euclid Deep Field North (EDFN), the existing LOFAR radio source catalogue, comprising 23,309 sources, is cross-matched with the Euclid Q1 data release to identify optical counterparts and obtain physical parameter estimates. This enables an extension of the radio-loud AGN fraction out to z = 3 and down to stellar masses of 10⁹ $M_☉$—a regime not previously accessible. The combined sensitivity and spatial resolution of Euclid and LOFAR enable the most robust statistical analysis of the radio-loud AGN fraction to date. We find that the power-law relation flattens significantly at lower stellar masses, indicating a departure from previously established trends. This transition suggests a connection to a change in the AGN accretion mode from a hot, radiatively inefficient mode at higher mass to a mode corresponding to cold gas accretion, triggered by galaxy mergers and interactions in under-dense environments. These findings offer new constraints on AGN-galaxy co-evolution models.
