LeMMINGs III. The e-MERLIN legacy survey of the Palomar sample: exploring the origin of nuclear radio emission in active and inactive galaxies through the [O III] - radio connection

What determines the nuclear radio emission in local galaxies? To address this question, we combine optical [O III] line emission, robust black hole (BH) mass estimates, and high-resolution e-MERLIN 1 .5-GHz data, from the LeMMINGs survey, of a statistically complete sample of 280 nearby optically active (LINER and Seyfert) and inactive [H II and absorption line galaxies (ALGs)] galaxies. Using [O III] luminosity (L-[o iii]) as a proxy for the accretion power, local galaxies follow distinct sequences in the optical-radio planes of BH activity, which suggest different origins of the nuclear radio emission for the optical classes. The 1 .5-GHz radio luminosity of their parsec-scale cores (L-core) is found to scale with BH mass (M-BH) and [O III] luminosity. Below M-BH similar to 10(6.5) M-circle dot, stellar processes from non-jetted H II galaxies dominate with (Lcore) proportional to M-BH(0.61 +/- 0.33) and L-core proportional to L-[Oiii](0.79 +/- 0.30). Above M-BH similar to 10(6.5) M-circle dot, accretion-driven processes dominate with L-core proportional to M-BH(1.5-1.65) and L-core proportional to L-[Oiii](0.99-1.31) for active galaxies: radio-quiet/loud LINERs, Seyferts, and jetted H II galaxies always display (although low) signatures of radio-emitting BH activity, with L-1.5GHz greater than or similar to 10(19.8) W Hz(-1) and M-BH greater than or similar to 10(7) M-circle dot, on a broad range of Eddington-scaled accretion rates ((m)over dot). Radio-quiet and radio-loud LINERs are powered by low-(m)over dot discs launching sub-relativistic and relativistic jets, respectively. Low-power slow jets and disc/corona winds from moderately high to high-(m)over dot discs account for the compact and edge-brightened jets of Seyferts, respectively. Jetted H II galaxies may host weakly active BHs. Fuel-starved BHs and recurrent activity account for ALG properties. In conclusion, specific accretion-ejection states of active BHs determine the radio production and the optical classification of local active galaxies.

Automated summary

The study combines optical line emission, black hole mass estimates, and radio data to investigate the factors determining the nuclear radio emission in local galaxies. Different types of galaxies display distinct nuclear radio emission characteristics, with specific accretion-ejection states of active black holes playing a crucial role.