We present the first data release of high-resolution ( 0.2 arcsec) 1.5-GHz radio images of 103 nearby galaxies from the Palomar sample, observed with the eMERLIN array, as part of the LeMMINGs survey. This sample includes galaxies which are active (LINER and Seyfert) and quiescent (Hii galaxies and Absorption line galaxies, ALG), which are reclassified based upon revised emission-line diagrams. We detect radio emission 0.2 mJy for 47/103 galaxies (22/34 for LINERS, 4/4 for Seyferts, 16/51 for Hii galaxies and 5/14 for ALGs) with radio sizes typically of 100 pc. We identify the radio core position within the radio structures for 41 sources. Half of the sample shows jetted morphologies. The remaining half shows single radio cores or complex morphologies. LINERs show radio structures more core-brightened than Seyferts. Radio luminosities of the sample range from 10 32 to 10 40 erg s −1 : LINERs and Hii galaxies show the highest and the lowest radio powers respectively, while ALGs and Seyferts have intermediate luminosities.We find that radio core luminosities correlate with black hole (BH) mass down to ∼10 7 M , but a break emerges at lower masses. Using [O III] line luminosity as a proxy for the accretion luminosity, active nuclei and jetted Hii galaxies follow an optical fundamental plane of BH activity, suggesting a common disc-jet relationship. In conclusion, LINER nuclei are the scaled-down version of FR I radio galaxies; Seyferts show less collimated jets; Hii galaxies may host weak active BHs and/or nuclear starforming cores; and recurrent BH activity may account for ALG properties.

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We present high-sensitivity eMERLIN radio images of the Seyfert galaxy NGC 4151 at 1.5 GHz. We compare the new eMERLIN images to those from archival MERLIN observations in 1993 to determine the change in jet morphology in the 22 years between observations. We report an increase by almost a factor of 2 in the peak flux density of the central core component, C4, thought to host the black hole, but a probable decrease in some other components, possibly due to adiabatic expansion. The core flux increase indicates an AGN which is currently active and feeding the jet. We detect no significant motion in 22 years between C4 and the component C3, which is unresolved in the eMERLIN image. We present a spectral index image made within the 512 MHz band of the 1.5 GHz observations. The spectrum of the core, C4, is flatter than that of other components further out in the jet. We use HST emission line images (Hα, [O III] and [O II]) to study the connection between the jet and the emission line region. Based on the changing emission line ratios away from the core and comparison with the eMERLIN radio jet, we conclude that photoionisation from the central AGN is responsible for the observed emission line properties further than 4 (360 pc) from the core, C4. Within this region, several evidences (radio-line co-spatiality, low [O III]/Hα and estimated fast shocks) suggest additional ionisation from the jet.

We present the highest sensitivity and angular resolution study at 0.32 GHz of the dwarf irregular galaxy IC 10, observed using the Giant Metrewave Radio Telescope, probing ∼ 45 pc spatial scales. We find the galaxy-averaged radio continuum spectrum to be relatively flat, with a spectral index α = −0.34 ± 0.01 (S ν ∝ ν α ), mainly due to a high contribution from free-free emission. At 0.32 GHz, some of the Hii regions show evidence of free-free absorption as they become optically thick below ∼ 0.41 GHz with corresponding free electron densities of ∼ 11 − 22 cm −3 . After removing the free-free emission, we studied the radio-infrared relations on 55, 110 and 165 pc spatial scales. We find that on all scales the non-thermal emission at 0.32 and 6.2 GHz correlates better with far-infrared (FIR) emission at 70 µm than mid-infrared emission at 24 µm. The dispersion of the radio-FIR relation arises due to variations in both magnetic field and dust temperature, and decreases systematically with increasing spatial scale. The effect of cosmic ray transport is negligible as cosmic ray electrons were only injected 5 Myr ago. The average magnetic field strength (B) of 12 µG in the disc is comparable to that of large star-forming galaxies. The local magnetic field is strongly correlated with local star formation rate (SFR) as B ∝ SFR 0.35±0.03 , indicating a star-burst driven fluctuation dynamo to be efficient (∼ 10 per cent) in amplifying the field in IC 10. The high spatial resolution observations presented here suggest that the high efficiency of magnetic field amplification and strong coupling with SFR likely sets up the radio-FIR correlation in cosmologically young galaxies.

We have analysed a new high-resolution e-MERLIN 1.5 GHz radio continuum map together with HST and SDSS imaging of NGC 5322, an elliptical galaxy hosting radio jets, aiming to understand the galaxy's central structure and its connection to the nuclear activity. We decomposed the composite HST + SDSS surface brightness profile of the galaxy into an inner stellar disc, a spheroid, and an outer stellar halo. Past works showed that this embedded disc counter-rotates rapidly with respect to the spheroid. The HST images reveal an edge-on nuclear dust disc across the centre, aligned along the major-axis of the galaxy and nearly perpendicular to the radio jets. After careful masking of this dust disc, we find a central stellar mass deficit M def in the spheroid, scoured by SMBH binaries with final mass M BH such that M def /M BH ∼ 1.3 − 3.4. We propose a three-phase formation scenario for NGC 5322 where a few (2 − 7) 'dry' major mergers involving SMBHs built the spheroid with a depleted core. The cannibalism of a gas-rich satellite subsequently creates the faint counter-rotating disc and funnels gaseous material directly onto the AGN, powering the radio core with a brightness temperature of T B,core ∼ 4.5 × 10 7 K and the low-power radio jets (P jets ∼ 7.04 × 10 20 W Hz −1 ) which extend ∼ 1.6 kpc. The outer halo can later grow via minor mergers and the accretion of tidal debris. The low-luminosity AGN/jet-driven feedback may have quenched the late-time nuclear star formation promptly, which could otherwise have replenished the depleted core.