We report deep EVN and eMERLIN observations of the Type Ia SN 2014J in the nearby galaxy M 82. Our observations represent, together with JVLA observations of SNe 2011fe and 2014J, the most sensitive radio studies of Type Ia SNe ever. By combining data and a proper modeling of the radio emission, we constrain the mass-loss rate from the progenitor system of SN 2014J toṀ 7.0 × 10 −10 M yr −1 (for a wind speed of 100 km s −1 ). If the medium around the supernova is uniform, then n ISM 1.3 cm −3 , which is the most stringent limit for the (uniform) density around a Type Ia SN. Our deep upper limits favor a double-degenerate (DD) scenario-involving two WD stars-for the progenitor system of SN 2014J, as such systems have less circumstellar gas than our upper limits. By contrast, most single-degenerate (SD) scenarios, i.e., the wide family of progenitor systems where a red giant, main-sequence, or sub-giant star donates mass to a exploding WD, are ruled out by our observations a . Our estimates on the limits to the gas density surrounding SN2011fe, using the flux density limits from Chomiuk et al. (2012), agree well with their results. Although we discuss possibilities for a SD scenario to pass observational tests, as well as uncertainties in the modeling of the radio emission, the evidence from SNe 2011fe and 2014J points in the direction of a DD scenario for both. a While completing our work, we noticed that a paper by Margutti et al. (2014) was submitted to The Astrophysical Journal. From a non-detection of X-ray emission from SN 2014J, the authors obtain limits ofṀ < ∼ 1.2 × 10 −9 M yr −1 (for a wind speed of 100 km s −1 ) and n ISM < ∼ 3.5 cm −3 , for the ρ ∝ r −2 wind and constant density cases, respectively. As these limits are less constraining than ours, the findings by Margutti et al. (2014) do not alter our conclusions. The X-ray results are, however, important to rule out free-free and synchrotron self-absorption as a reason for the radio non-detections.

The results of an extremely deep, 8‐d long observation of the central kpc of the nearby starburst galaxy M82 using Multi‐Element Radio Linked Interferometer Network (MERLIN) at 5 GHz are presented. The 17 μJy beam−1 rms noise level in the naturally weighted image makes it the most sensitive high‐resolution radio image of M82 made to date. Over 50 discrete sources are detected, the majority of which are supernova remnants, but with 13 identified as H ii regions. Sizes, flux densities and radio brightnesses are given for all of the detected sources, which are all well resolved with a majority showing shell or partial shell structures. Those sources within the sample which are supernova remnants have diameters ranging from 0.3 to 6.7 pc, with a mean size of 2.9 pc. From a comparison with previous MERLIN 5‐GHz observations made in 1992 July, which gives a 9.75‐yr timeline, it has been possible to measure the expansion velocities of 10 of the more compact sources, eight of which have not been measured before. These derived expansion velocities range between 2200 and 10 500 km s−1.

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.