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

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 5 σ threshold of 0.33 mJy beam ⁻¹ in 68/280 sources (24 per cent), with core luminosities 10 ³⁵ –10 ^{41 . 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 ≥ 10 ⁶ 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 -lik e 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.

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