LeMMINGs – I. The eMERLIN legacy survey of nearby galaxies. 1.5-GHz parsec-scale radio structures and cores

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 (low-ionization nuclear emission-line regions [LINER] and Seyfert) and quiescent (H II galaxies and absorption line galaxies, ALGs), 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 to 10 erg s: LINERs and HII galaxies show the highest and 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 M, but a break emerges at lower masses. Using [OIII] 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 star-forming cores; and recurrent BH activity may account for ALG properties.© 2018 The Author(s).
The authors thank the referee for a quick publication and the helpful comments from A. Laor and A. Capetti for the interpretation of the results. RDB and IMcH acknowledge the support of STFC under grant [ST/M001326/1] and IMcH thanks the Royal Society for the award of a Royal Society Leverhulme Trust Senior Research Fellowship. We acknowledge funding from the University of Southampton for a Mayflower studentship afforded to DW. EB and JW acknowledge support from the UK's Science and Technology Facilities Council [grant number ST/M503514/1] and [grant number ST/M001008/1], respectively. CGM acknowledges financial support from STFC. JHK acknowledges financial support from the European Union's Horizon 2020 research and innovation programme under Marie Sklodowska-Curie grant agreement No. 721463 to the SUNDIAL ITN network, and from the Spanish Ministry of Economy and Competitiveness (MINECO) under grant number AYA2016-76219-P. DMF wishes to acknowledge funding from an STFC Q10 consolidated grant [ST/M001334/1]. BTD acknowledges support from a Spanish postdoctoral fellowship 'Ayudas para la atraccion del talento investigador. Modalidad 2: jovenes investigadores, financiadas por la Comunidad de Madrid' under grant number 2016-T2/TIC-2039. FP has received funding from the European Union's Horizon 2020 Programme under the AHEAD project (grant agreement No. 654215). We also acknowledge the Jodrell Bank Centre for Astrophysics, which is funded by the STFC. eMERLIN and formerly MERLIN is a National Facility operated by the University of Manchester at Jodrell Bank Observatory on behalf of STFC. This publication has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No. 730562 [RadioNet].