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Disentangling the radio flux contribution from star formation (SF) and active-galactic-nuclei (AGN) activity is a long-standing problem in extragalactic astronomy, since at frequencies of $\lesssim$ 10 GHz, both processes emit synchrotron radiation. We present in this work the general objectives of the PARADIGM Project, a multi-instrument concept to explore star-formation and mass assembly of galaxies. We introduce two novel general approaches for a detailed multiscale study of the radio emission in local U/LIRGs. In this work, we use archival interferometric data from the Very Large Array (VLA) centred at ~ 6 GHz (C band) and present new observations from the e-Multi-Element Radio-Linked Interferometer Network (e-MERLIN) for UGC5101, VV705, VV250 and UGC8696. Using our image decomposition methods, we robustly disentangle the radio emission into distinct components by combining information from the two interferometric arrays. We use e-MERLIN as a probe of the core-compact radio emission (AGN or starburst) at ~ 20 pc scales, and as a probe of nuclear diffuse emission, at scales ~ 100 - 200 pc. With VLA, we characterise the source morphology and the flux density on scales from 200 pc up to and above 1 kpc. As a result, we find deconvolved and convolved sizes for nuclear regions from ~ 10 pc to ~ 200 pc. At larger scales, we find sizes of 1.5 - 2 kpc for diffuse structures (with effective sizes of ~ 300 - 400 pc). We demonstrate that the radio emission from nuclear extended structures (~ 100 pc) can dominate over core-compact components, providing a significant fraction of the total multiscale SF output. We establish a multiscale radio tracer for star formation by combining information from different instruments. Consequently, this work sets a starting point to potentially correct for overestimations of AGN fractions and underestimates of SF activity., Comment: Accepted for publication in MNRAS. 31 pages (9 pages appendix), 13 figures, 9 tables. Online code repository: morphen - https://github.com/lucatelli/morphen

3C84 is a nearby radio source with a complex total intensity structure, showing linear polarisation and spectral patterns. A detailed investigation of the central engine region necessitates the use of VLBI above the hitherto available maximum frequency of 86GHz. Using ultrahigh resolution VLBI observations at the highest available frequency of 228GHz, we aim to directly detect compact structures and understand the physical conditions in the compact region of 3C84. We used EHT 228GHz observations and, given the limited (u,v)-coverage, applied geometric model fitting to the data. We also employed quasi-simultaneously observed, multi-frequency VLBI data for the source in order to carry out a comprehensive analysis of the core structure. We report the detection of a highly ordered, strong magnetic field around the central, SMBH of 3C84. The brightness temperature analysis suggests that the system is in equipartition. We determined a turnover frequency of $\nu_m=(113\pm4)$GHz, a corresponding synchrotron self-absorbed magnetic field of $B_{SSA}=(2.9\pm1.6)$G, and an equipartition magnetic field of $B_{eq}=(5.2\pm0.6)$G. Three components are resolved with the highest fractional polarisation detected for this object ($m_\textrm{net}=(17.0\pm3.9)$%). The positions of the components are compatible with those seen in low-frequency VLBI observations since 2017-2018. We report a steeply negative slope of the spectrum at 228GHz. We used these findings to test models of jet formation, propagation, and Faraday rotation in 3C84. The findings of our investigation into different flow geometries and black hole spins support an advection-dominated accretion flow in a magnetically arrested state around a rapidly rotating supermassive black hole as a model of the jet-launching system in the core of 3C84. However, systematic uncertainties due to the limited (u,v)-coverage, however, cannot be ignored., Comment: 15 pages, 6 figures, published in A&A

The Event Horizon Telescope (EHT) observations carried out in 2018 April at 1.3 mm wavelengths included 9 stations in the array, comprising 7 single-dish telescopes and 2 phased arrays. The metadata package for the 2018 EHT observing campaign contains calibration tables required for the a-priori amplitude calibration of the 2018 April visibility data. This memo is the official documentation accompanying the release of the 2018 EHT metadata package, providing an overview of the contents of the package. We describe how telescope sensitivities, gain curves and other relevant parameters for each station in the EHT array were collected, processed, and validated to produce the calibration tables., Comment: 26 pages, 7 figures, EHT Memo Series 2023-L1-01

Starting from the observing campaign in April 2018, the Greenland Telescope (GLT) has been added as a new station of the Event Horizon Telescope (EHT) array. Visibilities on baselines to the GLT, particularly in the North-South direction, potentially provide valuable new constraints for the modeling and imaging of sources such as M87*. The GLT's location at high Northern latitudes adds unique challenges to its calibration strategies. Additionally, the performance of the GLT was not optimal during the 2018 observations due to it being only partially commissioned at the time. This document describes the steps taken to estimate the various parameters (and their uncertainties) required for the absolute flux calibration of the GLT data as part of the EHT. In particular, we consider the non-optimized status of the GLT in 2018, as well as its improved performance during the 2021 EHT campaign., Comment: 17 pages, 4 figures, EHT Memo Series 2023-L1-02

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 ($L_{\rm [O~III]}$) 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 ($L_{\rm core}$) is found to scale with BH mass ($M_{\rm BH}$) and [O~III] luminosity. Below $M_{\rm BH} \sim$10$^{6.5}$ M$_{\odot}$, stellar processes from non-jetted HII galaxies dominate with $L_{\rm core} \propto M_{\rm BH}^{0.61\pm0.33}$ and $L_{\rm core} \propto L_{\rm [O~III]}^{0.79\pm0.30}$. Above $M_{\rm BH} \sim$10$^{6.5}$ M$_{\odot}$, accretion-driven processes dominate with $L_{\rm core} \propto M_{\rm BH}^{1.5-1.65}$ and $L_{\rm core} \propto L_{\rm [O~III]}^{0.99-1.31}$ 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}\gtrsim$10$^{19.8}$ W Hz$^{-1}$ and $M_{\rm BH}\gtrsim10^{7}$ M$_{\odot}$, on a broad range of Eddington-scaled accretion rates ($\dot{m}$). Radio-quiet and radio-loud LINERs are powered by low-$\dot{m}$ discs launching sub-relativistic and relativistic jets, respectively. Low-power slow jets and disc/corona winds from moderately high to high-$\dot{m}$ 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], Comment: Accpeted for publication on MNRAS (27 pages, 9 Figures, 3 Tables, Appendix A)

We present the discovery and follow-up observations of two CCSNe that occurred in the luminous infrared galaxy (LIRG), NGC3256. The first, SN2018ec, was discovered using the ESO HAWK-I/GRAAL adaptive optics seeing enhancer, and was classified as a Type Ic with a host galaxy extinction of $A_V=2.1^{+0.3}_{-0.1}$ mag. The second, AT2018cux, was discovered during the course of follow-up observations of SN2018ec, and is consistent with a sub-luminous Type IIP classification with an $A_V=2.1 \pm 0.4$ mag of host extinction. A third CCSN, PSNJ10275082-4354034 in NGC3256, has previously been reported in 2014, and we recovered the source in late time archival HST imaging. Based on template light-curve fitting, we favour a Type IIn classification for it with modest host galaxy extinction of $A_V=0.3^{+0.4}_{-0.3}$ mag. We also extend our study with follow-up data of the recent Type IIb SN2019lqo and Type Ib SN2020fkb that occurred in the LIRG system Arp299 with host extinctions of $A_V=2.1^{+0.1}_{-0.3}$ and $A_V=0.4^{+0.1}_{-0.2}$ mag, respectively. Motivated by the above, we inspected, for the first time, a sample of 29 CCSNe located within a projected distance of 2.5 kpc from the host galaxy nuclei in a sample of 16 LIRGs. We find that, if star formation within these galaxies is modelled assuming a global starburst episode and normal IMF, there is evidence of a correlation between the starburst age and the CCSN subtype. We infer that the two subgroups of 14 H-poor (Type IIb/Ib/Ic/Ibn) and 15 H-rich (Type II/IIn) CCSNe have different underlying progenitor age distributions, with the H-poor progenitors being younger at 3$\sigma$ significance. However, we do note that the available sample sizes of CCSNe and host LIRGs are so far small, and the statistical comparisons between subgroups do not take into account possible systematic or model errors related to the estimated starburst ages. (abridged), Comment: 25 pages, 21 figures, accepted for publication in A&A

We present the second data release of high-resolution ($\leq0.2$ arcsec) 1.5-GHz radio images of 177 nearby galaxies from the Palomar sample, observed with the e-MERLIN array, as part of the LeMMINGs (Legacy e-MERLIN Multi-band Imaging of Nearby Galaxy Sample) survey. Together with the 103 targets of the first LeMMINGs data release, this represents a complete sample of 280 local active (LINER and Seyfert) and inactive galaxies HII galaxies and Absorption Line Galaxies, ALG). This large program is the deepest radio survey of the local Universe, $\gtrsim$10$^{17.6}$ W Hz$^{-1}$, regardless of the host and nuclear type: we detect radio emission $\gtrsim$0.25 mJy beam$^{-1}$ for 125/280 galaxies (44.6 per cent) with sizes of typically $\lesssim$100 pc. Of those 125, 106 targets show a core which coincides within 1.2 arcsec with the optical nucleus. Although we observed mostly cores, around one third of the detected galaxies features jetted morphologies. The detected radio core luminosities of the sample range between $\sim$10$^{34}$ and 10$^{40}$ erg s$^{-1}$. LINERs and Seyferts are the most luminous sources, whereas HII galaxies are the least. LINERs show FRI-like core-brightened radio structures, while Seyferts reveal the highest fraction of symmetric morphologies. The majority of HII galaxies have single radio core or complex extended structures, which probably conceal a nuclear starburst and/or a weak active nucleus (seven of them show clear jets). ALGs, which are typically found in evolved ellipticals, although the least numerous, exhibit on average the most luminous radio structures, similar to LINERs., Comment: Accepted for publication on MNRAS (48 pages, 7 figures, 10 tables, Appendix)

We present the discovery with Keck of the extremely infrared (IR) luminous transient AT 2017gbl, coincident with the Northern nucleus of the luminous infrared galaxy (LIRG) IRAS 23436+5257. Our extensive multi-wavelength follow-up spans ~900 days, including photometry and spectroscopy in the optical and IR, and (very long baseline interferometry) radio and X-ray observations. Radiative transfer modelling of the host galaxy spectral energy distribution and long-term pre-outburst variability in the mid-IR indicate the presence of a hitherto undetected dust obscured active galactic nucleus (AGN). The optical and near-IR spectra show broad 2000 km/s hydrogen, He I and O I emission features that decrease in flux over time. Radio imaging shows a fast evolving compact source of synchrotron emission spatially coincident with AT 2017gbl. We infer a lower limit for the radiated energy of 7.3 x 10^50 erg from the IR photometry. An extremely energetic supernova would satisfy this budget, but is ruled out by the radio counterpart evolution. Instead, we propose AT 2017gbl is related to an accretion event by the central supermassive black hole, where the spectral signatures originate in the AGN broad line region and the IR photometry is consistent with re-radiation by polar dust. Given the fast evolution of AT 2017gbl, we deem a tidal disruption event (TDE) of a star a more plausible scenario than a dramatic change in the AGN accretion rate. This makes AT 2017gbl the third TDE candidate to be hosted by a LIRG, in contrast to the so far considered TDE population discovered at optical wavelengths and hosted preferably by post-starburst galaxies., Comment: Accepted for publication by MNRAS. 32 pages, 22 figures

Tidal disruption events (TDEs) are transient flares produced when a star is ripped apart by the gravitational field of a supermassive black hole (SMBH). We have observed a transient source in the western nucleus of the merging galaxy pair Arp 299 that radiated >1.5x10^52 erg in the infrared and radio, but was not luminous at optical or X-ray wavelengths. We interpret this as a TDE with much of its emission re-radiated at infrared wavelengths by dust. Efficient reprocessing by dense gas and dust may explain the difference between theoretical predictions and observed luminosities of TDEs. The radio observations resolve an expanding and decelerating jet, probing the jet formation and evolution around a SMBH., Comment: Published online by Science on 14 Jun 2018

[abridged] Characterizing the number counts of faint, dusty star-forming galaxies is currently a challenge even for deep, high-resolution observations in the FIR-to-mm regime. They are predicted to account for approximately half of the total extragalactic background light at those wavelengths. Searching for dusty star-forming galaxies behind massive galaxy clusters benefits from strong lensing, enhancing their measured emission while increasing spatial resolution. Derived number counts depend, however, on mass reconstruction models that properly constrain these clusters. We estimate the 1.1 mm number counts along the line of sight of three galaxy clusters, i.e. Abell 2744, MACSJ0416.1-2403 and MACSJ1149.5+2223, which are part of the ALMA Frontier Fields Survey. We perform detailed simulations to correct these counts for lensing effects. We use several publicly available lensing models for the galaxy clusters to derive the intrinsic flux densities of our sources. We perform Monte Carlo simulations of the number counts for a detailed treatment of the uncertainties in the magnifications and adopted source redshifts. We find an overall agreement among the number counts derived for the different lens models, despite their systematic variations regarding source magnifications and effective areas. Our number counts span ~2.5 dex in demagnified flux density, from several mJy down to tens of uJy. Our number counts are consistent with recent estimates from deep ALMA observations at a 3$\sigma$ level. Below $\approx$ 0.1 mJy, however, our cumulative counts are lower by $\approx$ 1 dex, suggesting a flattening in the number counts. In our deepest ALMA mosaic, we estimate number counts for intrinsic flux densities $\approx$ 4 times fainter than the rms level. This highlights the potential of probing the sub-10 uJy population in larger samples of galaxy cluster fields with deeper ALMA observations., Comment: 19 pages, 14 figures, 3 tables. Accepted for publication in A&A

Recent all-sky surveys have led to the discovery of new types of transients. These include stars disrupted by the central supermassive black hole, and supernovae that are 10-100 times more energetic than typical ones. However, the nature of even more energetic transients that apparently occur in the innermost regions of their host galaxies is hotly debated. Here we report the discovery of the most energetic of these to date: PS1-10adi, with a total radiated energy of ~ 2.3 x 10^52 erg. The slow evolution of its light curve and persistently narrow spectral lines over ~3 yr are inconsistent with known types of recurring black hole variability. The observed properties imply powering by shock interaction between expanding material and large quantities of surrounding dense matter. Plausible sources of this expanding material are a star that has been tidally disrupted by the central black hole, or a supernova. Both could satisfy the energy budget. For the former, we would be forced to invoke a new and hitherto unseen variant of a tidally disrupted star, while a supernova origin relies principally on environmental effects resulting from its nuclear location. Remarkably, we also discovered that PS1-10adi is not an isolated case. We therefore surmise that this new population of transients has previously been overlooked due to incorrect association with underlying central black hole activity., Comment: Published in Nature Astronomy. 29 pages, 4 figures (main); 11 pages, 4 tables, 4 figures (supplementary)

Core collapse supernova (CCSN) rates suffer from large uncertainties as many CCSNe exploding in regions of bright background emission and significant dust extinction remain unobserved. Such a shortfall is particularly prominent in luminous infrared galaxies (LIRGs), which have high star formation (and thus CCSN) rates and host bright and crowded nuclear regions, where large extinctions and reduced search detection efficiency likely lead to a significant fraction of CCSNe remaining undiscovered. We present the first results of project SUNBIRD (Supernovae UNmasked By Infra-Red Detection), where we aim to uncover CCSNe that otherwise would remain hidden in the complex nuclear regions of LIRGs, and in this way improve the constraints on the fraction that is missed by optical seeing-limited surveys. We observe in the near-infrared 2.15 {\mu}m $K_s$-band, which is less affected by dust extinction compared to the optical, using the multi-conjugate adaptive optics imager GeMS/GSAOI on Gemini South, allowing us to achieve a spatial resolution that lets us probe close in to the nuclear regions. During our pilot program and subsequent first full year we have discovered three CCSNe and one candidate with projected nuclear offsets as small as 200 pc. When compared to the total sample of LIRG CCSNe discovered in the near-IR and optical, we show that our method is singularly effective in uncovering CCSNe in nuclear regions and we conclude that the majority of CCSNe exploding in LIRGs are not detected as a result of dust obscuration and poor spatial resolution., Comment: Accepted for publication in Monthly Notices of the Royal Astronomical Society, 19 pages, 11 figures

Hydrogen-poor superluminous supernovae (SLSNe-I) have been predominantly found in low-metallicity, star-forming dwarf galaxies. Here we identify Gaia17biu/SN 2017egm as an SLSN-I occurring in a "normal" spiral galaxy (NGC 3191) in terms of stellar mass (several times 10^10 M_sun) and metallicity (roughly Solar). At redshift z=0.031, Gaia17biu is also the lowest redshift SLSN-I to date, and the absence of a larger population of SLSNe-I in dwarf galaxies of similar redshift suggests that metallicity is likely less important to the production of SLSNe-I than previously believed. With the smallest distance and highest apparent brightness for an SLSN-I, we are able to study Gaia17biu in unprecedented detail. Its pre-peak near-ultraviolet to optical color is similar to that of Gaia16apd and among the bluest observed for an SLSN-I while its peak luminosity (M_g = -21 mag) is substantially lower than Gaia16apd. Thanks to the high signal-to-noise ratios of our spectra, we identify several new spectroscopic features that may help to probe the properties of these enigmatic explosions. We detect polarization at the ~0.5% level that is not strongly dependent on wavelength, suggesting a modest, global departure from spherical symmetry. In addition, we put the tightest upper limit yet on the radio luminosity of an SLSN-I with <5.4x10^26 erg/s/Hz (at 10 GHz), which is almost a factor of 40 better than previous upper limits and one of the few measured at an early stage in the evolution of an SLSN-I. This limit largely rules out an association of this SLSNe-I with known populations of gamma-ray burst (GRB) like central engines., Comment: Accepted for publication in ApJ. Ancillary ASCII tables added: TRL.txt -- blackbody temperature, radius and luminosity; uvw2uvm2uvw1uvu.txt -- UV photometry; BgVri.txt -- optical photometry; zJHK.txt -- NIR photometry

[abridged] The Hubble and Spitzer Space Telescope surveys of the Frontier Fields (FF) provide extremely deep images around six massive, strong-lensing clusters of galaxies. The ALMA FF survey aims to cover the same fields at 1.1mm, with maps reaching (unlensed) sensitivities of $<$70$\mu$Jy, in order to explore the properties of background dusty star-forming galaxies. We report on the multi-wavelength photometric analysis of all 12 significantly detected ($>$5$\sigma$) sources in the first three FF clusters observed by ALMA, based on data from Hubble and Spitzer, the VLT and Herschel. We measure the total photometry in all available bands and determine the photometric redshifts and the physical properties of the counterparts via SED-fitting. In particular, we carefully estimate the FIR photometry using 1.1mm priors to limit the misidentification of blended FIR counterparts, which strongly affect some flux estimates in previous FIR catalogs. We identify robust near-infrared (NIR) counterparts for all 11 sources with K$_s$ detection, the majority of which are quite red, with eight having $F814W-K_s\gtrsim 4$ and five having $F160W-[4.5]\gtrsim3$. From the FIR point of view, all our objects have $z_{phot}$$\sim$1--3, whereas based on the optical SED one object prefers a high-$z$ solution ($z\geq\ $7). Five objects among our sample have spectroscopic redshifts from the GLASS survey for which we can reproduce their SEDs with existing templates. This verification confirms the validity of our photometric redshift methodology. The mean redshift of our sample is $z_{phot}$=1.99$\pm$0.27. All 1.1mm selected objects are massive (10.0$<\log[M_{\star}(M_{\odot})]<$ 11.5), with high star formation rates ($<\log[SFR(M_{\odot}/yr)]> \approx$1.6) and high dust contents (8.1 $<\log[M_{dust} (M_{\odot})]<$8.8), consistent with previous ALMA surveys., Comment: 18 pages, 11 figures, accepted for publication in A&A

We present new SINFONI near-infrared integral field unit (IFU) spectroscopy and SALT optical long-slit spectroscopy characterising the history of a nearby merging luminous infrared galaxy, dubbed the Bird (IRAS19115-2114). The NIR line-ratio maps of the IFU data-cubes and stellar population fitting of the SALT spectra now allow dating of the star formation (SF) over the triple system uncovered from our previous adaptive optics data. The distinct components separate very clearly in a line-ratio diagnostic diagram. An off-nuclear pure starburst dominates the current SF of the Bird with 60-70% of the total, with a 4-7 Myr age, and signs of a fairly constant long-term star formation of the underlying stellar population. The most massive nucleus, in contrast, is quenched with a starburst age of >40 Myr and shows hints of budding AGN activity. The secondary massive nucleus is at an intermediate stage. The two major components have a population of older stars, consistent with a starburst triggered 1 Gyr ago in a first encounter. The simplest explanation of the history is that of a triple merger, where the strongly star forming component has joined later. We detect multiple gas flows in different phases. The Bird offers an opportunity to witness multiple stages of galaxy evolution in the same system; triggering as well as quenching of SF, and the early appearance of AGN activity. It also serves as a cautionary note on interpretations of observations with lower spatial resolution and/or without infrared data. At high-redshift the system would look like a clumpy starburst with crucial pieces of its puzzle hidden, in danger of misinterpretations., Comment: Submitted to MNRAS. 17 pages, 7 tables, 15 figures

When a star passes within the tidal radius of a supermassive black hole, it will be torn apart. For a star with the mass of the Sun ($M_\odot$) and a non-spinning black hole with a mass $<10^8 M_\odot$, the tidal radius lies outside the black hole event horizon and the disruption results in a luminous flare. Here we report observations over a period of 10 months of a transient, hitherto interpreted as a superluminous supernova. Our data show that the transient rebrightened substantially in the ultraviolet and that the spectrum went through three different spectroscopic phases without ever becoming nebular. Our observations are more consistent with a tidal disruption event than a superluminous supernova because of the temperature evolution, the presence of highly ionised CNO gas in the line of sight and our improved localisation of the transient in the nucleus of a passive galaxy, where the presence of massive stars is highly unlikely. While the supermassive black hole has a mass $> 10^8 M_\odot$, a star with the same mass as the Sun could be disrupted outside the event horizon if the black hole were spinning rapidly. The rapid spin and high black hole mass can explain the high luminosity of this event., Comment: Modified after proofs to match published version as much as possible. 56 pages, 12 figures, 2 tables, including Methods and Supplementary Information. A photometry file is linked here as ancillary file. All data (photometry and spectra) are also publicly available from WISeREP

SN 2005kd is among the most luminous supernovae (SNe) to be discovered at X-ray wavelengths. We have re-analysed all good angular resolution (better than $20"$ FWHM PSF) archival X-ray data for SN 2005kd. The data reveal an X-ray light curve that decreases as t$^{-1.62 \pm 0.06}$. Our modelling of the data suggests that the early evolution is dominated by emission from the forward shock in a high-density medium. Emission from the radiative reverse shock is absorbed by the cold dense shell formed behind the reverse shock. Our results suggest a progenitor with a mass-loss rate towards the end of its evolution of $\ge$ 4.3 $\times$ 10$^{-4} M_{\odot} \,{\rm yr}^{-1}$, for a wind velocity of 10 km s$^{-1}$, at 4.0 $\times$ 10$^{16}$ cm. This mass-loss rate is too high for most known stars, except perhaps hypergiant stars. A higher wind velocity would lead to a correspondingly higher mass-loss rate. A Luminous Blue Variable star undergoing a giant eruption could potentially fulfill this requirement, but would need a high mass-loss rate lasting for several hundred years, and need to explain the plateau observed in the optical light curve. The latter could perhaps be due to the ejecta expanding in the dense circumstellar material at relatively small radii. These observations are consistent with the fact that Type IIn SNe appear to expand into high density and high mass-loss rate environments, and also suggest rapid variability in the wind mass-loss parameters within at least the last 5000 years of stellar evolution prior to core-collapse., Comment: 11 pages, 2 tables and 4 figures. Accepted to MNRAS

Dusty star-forming galaxies are among the most prodigious systems at high redshift (z>1), characterized by high star formation rates and huge dust reservoirs. The bright end of this population has been well characterized in recent years, but considerable uncertainties remain for fainter dusty star-forming galaxies, which are responsible for the bulk of star formation at high redshift and thus play a key role in galaxy growth and evolution. In this first paper of our series, we describe our methods for finding high redshift faint dusty galaxies using millimeter observations with ALMA. We obtained ALMA 1.1 mm mosaic images for three strong-lensing galaxy clusters from the Frontier Fields survey. The 2'x2' mosaics overlap with the deep HST WFC3/IR footprints and encompass the high magnification regions of each cluster. The combination of extremely high ALMA sensitivity and the magnification power of these clusters allows us to systematically probe the sub-mJy population of dusty star-forming galaxies over a large surveyed area. We present a description of the reduction and analysis of the ALMA continuum observations for the galaxy clusters Abell 2744 (z=0.308), MACSJ0416.1-2403 (z=0.396) and MACSJ1149.5+2223 (z=0.543), for which we reach observed rms sensitivities of 55, 59 and 71 $\mu$Jy beam$^{-1}$ respectively. We detect 12 dusty star-forming galaxies at S/N>5.0 across the three clusters, all of them presenting coincidence with NIR detected counterparts in the HST images. None of the sources fall close to the lensing caustics, thus they are not strongly lensed. The observed 1.1 mm flux densities for the total sample of galaxies range from 0.41 to 2.82 mJy, with observed effective radii spanning <0.05" to 0.37"$\pm$0.21". The lensing-corrected sizes of the detected sources appear to be in the same range as those measured in brighter samples, albeit with possibly larger dispersion., Comment: Accepted for publication in A&A. New version addressing last referee comments, 17 pages and 12 figures

We report the detection of a heavily obscured Active Galactic Nucleus (AGN) in the luminous infrared galaxy (LIRG) NGC 6286, identified in a 17.5 ks NuSTAR observation. The source is in an early merging stage, and was targeted as part of our ongoing NuSTAR campaign observing local luminous and ultra-luminous infrared galaxies in different merger stages. NGC 6286 is clearly detected above 10 keV and, by including the quasi-simultaneous Swift/XRT and archival XMM-Newton and Chandra data, we find that the source is heavily obscured [$N_{\rm\,H}\simeq (0.95-1.32)\times 10^{24}\rm\,cm^{-2}$], with a column density consistent with being Compton-thick [CT, $\log (N_{\rm\,H}/\rm cm^{-2})\geq 24$]. The AGN in NGC 6286 has a low absorption-corrected luminosity ($L_{2-10\rm\,keV}\sim 3-20\times 10^{41}\rm\,erg\,s^{-1}$) and contributes $\lesssim$1\% to the energetics of the system. Because of its low-luminosity, previous observations carried out in the soft X-ray band ($<10$ keV) and in the infrared did not notice the presence of a buried AGN. NGC 6286 has multi-wavelength characteristics typical of objects with the same infrared luminosity and in the same merger stage, which might imply that there is a significant population of obscured low-luminosity AGN in LIRGs that can only be detected by sensitive hard X-ray observations., Comment: Accepted for publication in ApJ, 14 pages, 7 figures

We present photometric and spectroscopic observations of SN 2013fc, a bright type II supernova (SN) in a circumnuclear star-forming ring in the luminous infrared galaxy ESO 154-G010, observed as part of the Public ESO Spectroscopic Survey of Transient Objects (PESSTO). SN 2013fc is both photometrically and spectroscopically similar to the well-studied type IIn SN 1998S and to the bright type II-L SN 1979C. It exhibits an initial linear decline, followed by a short plateau phase and a tail phase with a decline too fast for $^{56}$Co decay with full gamma-ray trapping. Initially the spectrum was blue and featureless. Later on, a strong broad ($\sim 8000$ km s$^{-1}$) H $\alpha$ emission profile became prominent. We apply a Starlight stellar population model fit to the SN location (observed when the SN had faded) to estimate a high extinction of $A_V = 2.9 \pm 0.2$ mag and an age of $10_{-2}^{+3}$ Myr for the underlying cluster. We compare the SN to SNe 1998S and 1979C and discuss its possible progenitor star considering the similarities to these events. With a peak brightness of $B = -20.46 \pm 0.21$ mag, SN 2013fc is 0.9 mag brighter than SN 1998S and of comparable brightness to SN 1979C. We suggest that SN 2013fc was consistent with a massive red supergiant (RSG) progenitor. Recent mass loss probably due to a strong RSG wind created the circumstellar matter illuminated through its interaction with the SN ejecta. We also observe a near-infrared excess, possibly due to newly condensed dust., Comment: 27 pages, 15 figures; accepted for publication in MNRAS

We present new NuSTAR and Chandra observations of NGC 3393, a galaxy reported to host the smallest separation dual AGN resolved in the X-rays. While past results suggested a 150 pc separation dual AGN, three times deeper Chandra imaging, combined with adaptive optics and radio imaging suggest a single, heavily obscured, radio-bright AGN. Using VLA and VLBA data, we find an AGN with a two-sided jet rather than a dual AGN and that the hard X-ray, UV, optical, NIR, and radio emission are all from a single point source with a radius <0.2". We find that the previously reported dual AGN is most likely a spurious detection resulting from the low number of X-ray counts (<160) at 6-7 keV and Gaussian smoothing of the data on scales much smaller than the PSF (0.25" vs. 0.80" FWHM). We show that statistical noise in a single Chandra PSF generates spurious dual peaks of the same separation (0.55$\pm$0.07" vs. 0.6") and flux ratio (39$\pm$9% vs. 32% of counts) as the purported dual AGN. With NuSTAR, we measure a Compton-thick source (NH=$2.2\pm0.4\times10^{24}$ cm$^{-2}$) with a large torus half-opening angle, {\theta}=79 which we postulate results from feedback from strong radio jets. This AGN shows a 2-10 keV intrinsic to observed flux ratio of 150. Using simulations, we find that even the deepest Chandra observations would severely underestimate the intrinsic luminosity of NGC 3393 above z>0.2, but would detect an unobscured AGN of this luminosity out to high redshift (z=5)., Comment: Accepted for publication in ApJ. 15 Figures and 4 tables

The Public European Southern Observatory Spectroscopic Survey of Transient Objects (PESSTO) began as a public spectroscopic survey in April 2012. We describe the data reduction strategy and data products which are publicly available through the ESO archive as the Spectroscopic Survey Data Release 1 (SSDR1). PESSTO uses the New Technology Telescope with EFOSC2 and SOFI to provide optical and NIR spectroscopy and imaging. We target supernovae and optical transients brighter than 20.5mag for classification. Science targets are then selected for follow-up based on the PESSTO science goal of extending knowledge of the extremes of the supernova population. The EFOSC2 spectra cover 3345-9995A (at resolutions of 13-18 Angs) and SOFI spectra cover 0.935-2.53 micron (resolutions 23-33 Angs) along with JHK imaging. This data release contains spectra from the first year (April 2012 - 2013), consisting of all 814 EFOSC2 spectra and 95 SOFI spectra (covering 298 distinct objects), in standard ESO Phase 3 format. We estimate the accuracy of the absolute flux calibrations for EFOSC2 to be typically 15%, and the relative flux calibration accuracy to be about 5%. The PESSTO standard NIR reduction process does not yet produce high accuracy absolute spectrophotometry but the SOFI JHK imaging will improve this. Future data releases will focus on improving the automated flux calibration of the data products., Comment: Accepted for publication in A&A. Describes the PESSTO public data products. All reduced data available from the ESO archive. See http://www.pessto.org for download instructions

Core-collapse SNe (CCSNe): Systematic searches of radio emission from CCSNe are still lacking, and only targeted searches of radio emission from just some of the optically discovered CCSNe in the local universe have been carried out. Optical searches miss a significant fraction of CCSNe due to dust obscuration; CCSN radio searches are thus more promising for yielding the complete, unobscured star-formation rates in the local universe. The SKA yields the possibility to piggyback for free in this area of research by carrying out commensal, wide-field, blind transient survey observations. SKA1-SUR should be able to discover several hundreds of CCSNe in just one year, compared to about a dozen CCSNe that the VLASS would be able to detect in one year, at most. SKA, with an expected sensitivity ten times that of SKA1, is expected to detect CCSNe in the local Universe by the thousands. Therefore, commensal SKA observations could easily result in an essentially complete census of all CCSNe in the local universe, thus yielding an accurate determination of the volumetric CCSN rate. Type Ia SNe: We advocate for the use of the SKA to search for the putative prompt (~first few days after the explosion) radio emission of any nearby type Ia SN, via target-of-opportunity observations. The huge improvement in sensitivity of the SKA with respect to its predecessors will allow to unambiguously discern which progenitor scenario (single-degenerate vs. double-degenerate) applies to them., Comment: Proceedings of Science: Advancing Astrophysics with the Square Kilometre Array. Accepted version, including comments by the referee

We present a photometric and spectroscopic study of a reddened type Ic supernova (SN) 2005at. We report our results based on the available data of SN 2005at, including late-time observations from the Spitzer Space Telescope and the Hubble Space Telescope. In particular, late-time mid-infrared observations are something rare for type Ib/c SNe. In our study we find SN 2005at to be very similar photometrically and spectroscopically to another nearby type Ic SN 2007gr, underlining the prototypical nature of this well-followed type Ic event. The spectroscopy of both events shows similar narrow spectral line features. The radio observations of SN 2005at are consistent with fast evolution and low luminosity at radio wavelengths. The late-time Spitzer data suggest the presence of an unresolved light echo from interstellar dust and dust formation in the ejecta, both of which are unique observations for a type Ic SN. The late-time Hubble observations reveal a faint point source coincident with SN 2005at, which is very likely either a declining light echo of the SN or a compact cluster. For completeness we study ground-based pre-explosion archival images of the explosion site of SN 2005at, however this only yielded very shallow upper limits for the SN progenitor star. We derive a host galaxy extinction of $A_{V} \approx 1.9$ mag for SN 2005at, which is relatively high for a SN in a normal spiral galaxy not viewed edge-on., Comment: 13 pages, 13 figures. Minor changes in text from v1. Published in A&A

We report radio observations of two stripped-envelope supernovae (SNe), 2010O and 2010P, which exploded within a few days of each other in the luminous infrared galaxy Arp 299. Whilst SN 2010O remains undetected at radio frequencies, SN 2010P was detected (with an astrometric accuracy better than 1 milli arcsec in position) in its optically thin phase in epochs ranging from ~1 to ~3yr after its explosion date, indicating a very slow radio evolution and a strong interaction of the SN ejecta with the circumstellar medium. Our late-time radio observations toward SN 2010P probe the dense circumstellar envelope of this SN, and imply a mass-loss rate (Msun/yr) to wind velocity (in units of 10 km/s) ratio of (3.0-5.1)E-05, with a 5 GHz peak luminosity of ~1.2E+27 erg/s/Hz on day ~464 after explosion. This is consistent with a Type IIb classification for SN 2010P, making it the most distant and most slowly evolving Type IIb radio SN detected to date., Comment: 14 pages, 8 tables and 7 figures. Accepted for publication in MNRAS

Observations spanning a large wavelength range, from X-ray to radio, of the Type IIb supernova 2011hs are presented, covering its evolution during the first year after explosion. The optical light curve presents a narrower shape and a fainter luminosity at peak than previously observed for Type IIb SNe. High expansion velocities are measured from the broad absorption H I and He I lines. From the comparison of the bolometric light curve and the time evolution of the photospheric velocities with hydrodynamical models, we found that SN 2011hs is consistent with the explosion of a 3-4 Msun He-core progenitor star, corresponding to a main sequence mass of 12-15 Msun, that ejected a mass of 56Ni of about 0.04 Msun, with an energy of E= 8.5 x 10^50 erg. Such a low-mass progenitor scenario is in full agreement with the modelling of the nebular spectrum taken at $\sim$215 days from maximum. From the modelling of the adiabatic cooling phase, we infer a progenitor radius of $\approx$500-600 Rsun, clearly pointing to an extended progenitor star. The radio light curve of SN 2011hs yields a peak luminosity similar to that of SN 1993J, but with a higher mass loss rate and a wind density possibly more similar to that of SN 2001ig. Although no significant deviations from a smooth decline have been found in the radio light curves, we cannot rule out the presence of a binary companion star., Comment: 25 pages, 19 figures, 10 tables. Accepted for publication in MNRAS

We present near-infrared and optical photometry, plus optical spectroscopy of two stripped-envelope supernovae (SNe) 2010O and 2010P that exploded in two different components of an interacting luminous infrared galaxy Arp 299 within only a few days of one another. SN 2010O is found to be photometrically and spectroscopically similar to many normal Type Ib SNe and our multiwavelength observations of SN 2010P suggest it to be a Type IIb SN. No signs of clear hydrogen features or interaction with the circumstellar medium are evident in the optical spectrum of SN 2010P. We derive estimates for the host galaxy line-of-sight extinctions for both SNe, based on both light-curve and spectroscopic comparison finding consistent results. These methods are also found to provide much more robust estimates of the SN host galaxy reddening than the commonly used empirical relations between extinction and equivalent width of Na I D absorption features. The SN observations also suggest that different extinction laws are present in different components of Arp 299. For completeness, we study high-resolution pre-explosion images of Arp 299 and find both SNe to be close to, but not coincident with, extended sources that are likely massive clusters. A very simple model applied to the bolometric light curve of SN 2010O implies a rough estimate for the explosion parameters of $E_{\mathrm{k}} \approx 3 \times 10^{51}$ erg, $M_{\mathrm{ej}} \approx 2.9$ M$_{\odot}$ and $M_{\mathrm{Ni}} \approx 0.16$ M$_{\odot}$., Comment: 16 pages, 11 figures. Minor changes in text from v1. Published in MNRAS

We present optical and near-infrared (IR) photometry and near-IR spectroscopy of SN 2004am, the only optically detected supernova (SN) in M 82. These demonstrate that SN 2004am was a highly reddened type II-P SN similar to the low luminosity type II-P events such as SNe 1997D and 2005cs. We show that SN 2004am was located coincident with the obscured super star cluster M 82-L, and from the cluster age infer a progenitor mass of 12 +7/-3 Msun. In addition to this, we present a high spatial resolution Gemini-N K-band adaptive optics image of the site of SN 2008iz and a second transient of uncertain nature, both detected so far only at radio wavelengths. Using image subtraction techniques together with archival data from the Hubble Space Telescope, we are able to recover a near-IR transient source co-incident with both objects. We find the likely extinction towards SN 2008iz to be not more than Av ~ 10. The nature of the second transient remains elusive and we regard an extremely bright microquasar in M 82 as the most plausible scenario., Comment: 14 pages, 8 figures, accepted for publication in MNRAS

The high star formation rates of luminous infrared galaxies (LIRGs) make them ideal places for core-collapse supernova (CCSN) searches. At radio frequencies, free from dust extinction, it is possible to detect compact components within the innermost LIRG nuclear regions, such as SNe and SN remnants, as well as AGN buried deep in the LIRG nuclei. We studied the LIRG IC883 aiming at: (i) investigating its (circum-)nuclear regions using the e-EVN at 5GHz, and e-MERLIN at 6.9GHz, complemented by archival VLBI data; (ii) detecting at radio frequencies the two recently reported circumnuclear SNe 2010cu and 2011hi, which were discovered by near-IR (NIR) adaptive optics observations of IC883; and (iii) further investigating the nature of SN2011hi at NIR by means of observations with Gemini-North. The circumnuclear regions traced by e-MERLIN at 6.9GHz have an extension of ~1kpc, and show a striking double-sided structure, which very likely corresponds to a warped rotating ring, in agreement with previous studies. Our e-EVN observations at 5GHz and complementary archival VLBI data at 5GHz and 8.4GHz, reveal the presence of various milliarcsec compact components in the nucleus of IC883. A single compact source, an AGN candidate, dominates the emission at both nuclear and circumnuclear scales, as imaged with the e-EVN and e-MERLIN, respectively. The other milliarcsec components are very suggestive of ongoing nuclear CCSN activity. Our e-EVN observations also resulted in upper limits to the radio luminosity of the two SNe in IC883 recently discovered at NIR. We refine the classification of SN2011hi as a Type IIP SN according to our latest Gemini-North epoch from 2012, in agreement with a low-luminosity radio SN nature. We estimate a CCSN rate lower limit of 1.1_{-0.6}^{+1.3} yr^{-1} for the entire galaxy, based on three nuclear radio SNe and the circumnuclear SNe 2010cu and 2011hi. (abridged), Comment: 9 pages, 5 figures and 2 tables. Accepted for publication in A&A

We report the discovery of two consecutive supernovae (SNe), 2010cu and 2011hi, located at 0.37" (180 pc) and 0.79" (380 pc) projected distance respectively from the centre of the K-band nucleus of the luminous infrared galaxy IC 883. The SNe were discovered in an ongoing near-infrared K-band search for core-collapse SNe in such galaxies using the ALTAIR/NIRI adaptive optics system with laser guide star at the Gemini-North Telescope. These are thus the closest SNe yet discovered to a LIRG nucleus in optical or near-infrared wavelengths. The near-infrared light curves and colours of both SNe are consistent with core-collapse events. Both SNe seem to suffer from relatively low host galaxy extinction suggesting that regardless of their low projected galactocentric distances, they are not deeply buried in the nuclear regions of the host galaxy., Comment: 6 pages, 3 figures, accepted for ApJ Letters

Context. The central kiloparsec of many local Luminous Infra-red Galaxies are known to host intense bursts of massive star formation, leading to numerous explosions of core-collapse supernovae (CCSNe). However, the dust-enshrouded regions where those supernovae explode hamper their detection at optical and near-infrared wavelengths. Aims. We investigate the nuclear region of the starbust galaxy IC 694 (=Arp 299-A) at radio wavelengths, aimed at discovering recently exploded CCSNe, as well as to determine their rate of explosion, which carries crucial information on star formation rates, the initial mass function and starburst scenarios at work. Methods. We use the electronic European VLBI Network to image with milliarcsecond resolution the 5.0 GHz compact radio emission of the innermost nuclear region of IC 694. Results. Our observations reveal the presence of a rich cluster of 26 compact radio emitting sources in the central 150 pc of the nuclear starburst in IC 694. The large brightness temperatures observed for the compact sources indicate a non-thermal origin for the observed radio emission, implying that most, if not all, of those sources are young radio supernovae (RSNe) and supernova remnants (SNRs). We find evidence for at least three relatively young, slowly-evolving, long-lasting RSNe (A0, A12, and A15) which appear to display unusual properties; suggesting that the conditions in the local circumstellar medium (CSM) play a significant role in determining the radio behaviour of expanding SNe. Their radio luminosities are typical of normal RSNe, which result from the explosion of Type IIP/b and Type IIL SNe. All these results yield support for a recent (less than 10-15 Myr) instantaneous starburst in the innermost regions of IC 694., Comment: Accepted for publication in A&A Letters. 8 pages, 3 figures, 2 tables

We report the discovery of a confirmed supernova (SN) and a supernova-candidate in near-infrared images from the ALTAIR/NIRI adaptive optics system on the Gemini-North Telescope and NICMOS on the Hubble Space Telescope. The Gemini images were obtained as part of a near-infrared K-band search for highly-obscured SNe in the nuclear regions of luminous infrared galaxies. SN 2008cs apparent in the Gemini images is the first SN discovered using laser guide star adaptive optics. It is located at 1500 pc projected distance from the nucleus of the luminous infrared galaxy IRAS 17138-1017. The SN luminosity, JHK colors and light curve are consistent with a core-collapse event suffering from a very high host galaxy extinction of 15.7 +- 0.8 magnitudes in V-band which is to our knowledge the highest yet measured for a SN. The core-collapse nature of SN 2008cs is confirmed by its radio detection at 22.4 GHz using our Very Large Array observations 28 days after the SN discovery, indicating a prominent interaction of the SN ejecta with the circumstellar medium. An unconfirmed SN apparent in the NICMOS images from 2004 is located in the same galaxy at 660 pc projected distance from the nucleus and has a lower extinction., Comment: 4 pages, 4 figures, ApJ Letters in press. The SN candidate from 2004 has been assigned the designation SN 2004iq (Kankare et al. 2008, CBET 1569, 1)