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

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Williams, DRA 
Beswick, RJ 
Mchardy, I 
Dullo, BT 

What determines the nuclear radio emission in local galaxies? 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 HII and Absorption line galaxies [ALG]) 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 (Lcore) is found to scale with BH mass (MBH) and [O~III] luminosity. Below $M_{\rm BH} \sim10^{6.5}$ M, stellar processes from non-jetted HII galaxies dominate with LcoreMBH0.61±0.33 and LcoreL[O III]0.79±0.30. Above $M_{\rm BH} \sim10^{6.5}$ M, accretion-driven processes dominate with LcoreMBH1.5−1.65 and LcoreL[O III]0.99−1.31 for active galaxies: radio-quiet/loud LINERs, Seyferts and jetted HII galaxies always display (although low) signatures of radio-emitting BH activity, with $L_{\rm 1.5, GHz}\gtrsim10^{19.8}$ W Hz−1 and MBH≳107 M, on a broad range of Eddington-scaled accretion rates (m˙). Radio-quiet and radio-loud LINERs are powered by low-m˙ discs launching sub-relativistic and relativistic jets, respectively. Low-power slow jets and disc/corona winds from moderately high to high-m˙ discs account for the compact and edge-brightened jets of Seyferts, respectively. Jetted HII galaxies may host weakly active BHs. Fuel-starved BHs and recurrent activity account for ALG properties. [abridged]

galaxies: active, galaxies: jets, galaxies: nuclei, galaxies: star formation, radio continuum: galaxies
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Monthly Notices of the Royal Astronomical Society
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Oxford University Press (OUP)
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