LeMMINGs VII: 5-GHz 50-mas e-MERLIN observations of a statistically complete sample of nearby AGNs

Abstract

We present 5 GHz e-MERLIN radio images at 50 mas resolution of the nuclear regions of the Legacy e-MERLIN Multi-band Imaging of Nearby Galaxies survey (LeMMINGs): the deepest statistically complete radio-band survey of the local Universe ( <120 Mpc), consisting of 280 galaxies spanning all morphological and nuclear types. We detect nuclear radio emission above a median 5σ threshold of 0.33 mJy beam −1 in 68/280 sources (24 per cent), with core luminosities 1035 ─ 1041.9 erg s −1.The radio emission is attributed to active galactic nuclei (AGNs), circumnuclear star formation, or ─ in the case of NGC 3690 ─ a tidal disruption event. The brightest radio nuclei, with brightness temperatures ≥106 K, reside in optically 'active' galaxies ─ LINERs and Seyferts. The detection rate for 'inactive' systems (H II and absorption-line galaxies), which may host low-luminosity AGNs (LLAGNs), is 8 per cent. Most detections (78 per cent) are compact ( <10 pc), while the remaining 22 per cent show extended jet-like features (up to 380 pc). Compared to 1.5 GHz LeMMINGs data, the 5 GHz observations' superior resolution and spatial filtering resolve out large-scale structures, isolating genuine nuclear emission. Our results suggest that LLAGNs are the primary manifestation of black-hole activity in the local Universe in the form of compact jets and cores, with a preference for early-type hosts. The two LeMMINGs campaigns show that up to 30 per cent of the local galaxy population host a radio-active nucleus, highlighting the necessity of high-resolution high-sensitivity imaging for uncovering nuclear emission at the lowest luminosities.