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The relation between nuclear star clusters (NSCs) and the growth of the central supermassive black holes (SMBHs), as well as their connection to the properties of the host galaxies, is crucial for understanding the evolution of galaxies. Recent observations have revealed that about 10 per cent of nucleated galaxies host hybrid nuclei, consisting of both NSCs and accreting SMBHs that power active galactic nuclei (AGNs). Motivated by the potential of the recently published multiwavelength data sets from LeMMINGs survey, here we present the most thorough investigation to date of the incidence of hybrid nuclei in a large sample of 100 nearby nucleated galaxies (10 E, 25 S0, 63 S, and 2 Irr), covering a wide range in stellar mass (⁠|$M_{*,\rm gal} \sim 10^{8.7}-10^{12}~\rm M_{\odot }$|⁠). We identify the nuclei and derive their properties by performing detailed 1D and 2D multicomponent decompositions of the optical and near-infrared HST stellar light distributions of the galaxies using Sérsic and core-Sérsic models. Our AGN diagnostics are based on homogeneously derived nuclear 1.5 GHz e -MERLIN radio, Chandra X-ray (0.3–10 keV), and optical emission-line data. We determine the nucleation fraction (⁠|$f_{\rm nuc}$|⁠) as the relative incidence of nuclei across the LeMMINGs HST sample and find |$f_{\rm nuc} =~$| 100/149 (= 67 |$\pm$| 7 per cent), confirming previous work, with a peak value of |$49/56~(= 88 \pm 13$|  per cent) at bulge masses |$M_{*,\rm bulge}\sim 10^{9.4}- 10^{10.8}~ \rm M_{\odot }$|⁠. We identify 30 nucleated LeMMINGs galaxies that are optically active, radio-detected, and X-ray luminous (⁠|$L_\textnormal {X} \gt 10^{39}$| erg s |$^{-1}$|⁠). This indicates that our nucleated sample has a lower limit |$\sim$| 30 per cent occupancy of hybrid nuclei, which is a function of |$M_{*,\rm bulge}$| and |$M_{*,\rm gal}$|⁠. We find that hybrid nuclei have a number density of |$(1.5 \pm 0.4)\times 10^{-5}$|  Mpc |$^{-3}$|⁠ , are more common at |$M_{*,\rm gal}\sim 10^{10.6}- 10^{11.8}~\rm M_{\odot }$| and occur, at least, three times more frequently than previously reported. [ABSTRACT FROM AUTHOR]

Deep radio surveys of extragalactic legacy fields trace a large range of spatial and brightness temperature sensitivity scales, and therefore have differing biases to radio-emitting physical components within galaxies. This is particularly true of radio surveys performed at |$\lesssim 1 \ \mathrm{arcsec}$| angular resolutions, and so robust comparisons are necessary to better understand the biases present in each survey. We present a multiresolution and multiwavelength analysis of the sources detected in a new Very Long Baseline Array (VLBA) survey of the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey Great Observatories Origins Deep Survey-North field. For the 24 VLBA-selected sources described in Paper I, we augment the VLBA data with EVN data, and ∼0.1–1 arcsec angular resolution data provided by Very Large Array (VLA) and enhanced-Multi Element Remotely Linked Interferometry Network. This sample includes new active galactic nuclei (AGN) detected in this field, thanks to a new source extraction technique that adopts priors from ancillary multiwavelength data. The high brightness temperatures of these sources (TB ≳ 106 K) confirm AGN cores, that would often be missed or ambiguous in lower-resolution radio data of the same sources. Furthermore, only 15 sources are identified as 'radiative' AGN based on available X-ray and infrared constraints. By combining VLA and VLBA measurements, we find evidence that the majority of the extended radio emission is also AGN dominated, with only three sources with evidence for extended potentially star formation-dominated radio emission. We demonstrate the importance of wide-field multiresolution (arcsecond–milliarcsecond) coverage of the faint radio source population, for a complete picture of the multiscale processes within these galaxies. [ABSTRACT FROM AUTHOR]

The point-spread function (PSF) is a fundamental property of any astronomical instrument. In interferometers, differing array configurations combined with their uv coverage, and various weighting schemes can produce an irregular but deterministic PSF. As a result, the PSF is often deconvolved using CLEAN-style algorithms to improve image fidelity. In this paper, we revisit a significant effect that causes the flux densities measured with any interferometer to be systematically offset from the true values. Using a suite of carefully controlled simulations, we show that the systematic offset originates from a mismatch in the units of the image produced by these CLEAN-style algorithms. We illustrate that this systematic error can be significant, ranging from a few to tens of per cent. Accounting for this effect is important for current and future interferometric arrays, such as MeerKAT, LOFAR, and the SKA, whose core-dominated configuration naturally causes an irregular PSF. We show that this offset is independent of other systematics, and can worsen due to some factors such as the goodness of the fit to the PSF, the deconvolution depth, and the signal-to-noise ratio of the source. Finally, we present several methods that can reduce this effect to just a few per cent. [ABSTRACT FROM AUTHOR]

Multiwavelength studies indicate that nuclear activity and bulge properties are closely related, but the details remain unclear. To study this further, we combine Hubble Space Telescope bulge structural and photometric properties with 1.5 GHz, e -MERLIN nuclear radio continuum data from the LeMMINGs survey for a large sample of 173 'active' galaxies (LINERs and Seyferts) and 'inactive' galaxies (H  ii s and absorption line galaxies, ALGs). Dividing our sample into active and inactive, they define distinct (radio core luminosity)–(bulge mass), |$L_{\rm R,core}-M_{*, \rm bulge}$| , relations, with a mass turnover at |$M_{*, \rm bulge}\sim 10^{9.8 \pm 0.3} \rm { M_{\odot }}$| (supermassive blackhole mass |$M_{\rm BH} \sim 10^{6.8 \pm 0.3} \rm M_{\odot }$|), which marks the transition from AGN-dominated nuclear radio emission in more massive bulges to that mainly driven by stellar processes in low-mass bulges. None of our 10/173 bulge-less galaxies host an AGN. The AGN fraction increases with increasing |$M_{*,\rm bulge}$| such that |$f_{\rm optical\_AGN}\propto M_{*,\rm bulge}^{0.24 \pm 0.06}$| and |$f_{\rm radio\_AGN}\propto M_{*,\rm bulge}^{0.24 \pm 0.05}$|. Between |$M_{*,\rm bulge}\sim 10^{8.5}$| and |$10^{11.3} \rm M_{\odot }$| , |$f_{\rm optical\_AGN}$| steadily rises from 15 ± 4 to 80 ± 5 per cent. We find that at fixed bulge mass, the radio loudness, nuclear radio activity, and the (optical and radio) AGN fraction exhibit no dependence on environment. Radio-loud hosts preferentially possess an early-type morphology than radio-quiet hosts, the two types are however indistinguishable in terms of bulge Sérsic index and ellipticity, while results on the bulge inner logarithmic profile slope are inconclusive. We finally discuss the importance of bulge mass in determining the AGN triggering processes, including potential implications for the nuclear radio emission in nearby galaxies. [ABSTRACT FROM AUTHOR]

We present analysis of comprehensive radio observations of the black hole V404 Cyg during its 2015 outburst. These data represent the best ever coverage of jet production and particle acceleration from any black hole. We report for the first time a clear and near-linear flux–rms correlation in the radio flux densities. Investigation of individual flares reveals in nearly all cases the peak corresponds to the transition from optically thick to thin to synchrotron emission, but an extended phase of particle acceleration is required in contrast to simple impulsive injection models. The largest radio flare is preceded by a phase of optical oscillations and followed one day later by a smaller but optically thin flare, likely due to ejecta interacting with the interstellar medium. Comparing the radio emission to contemporaneous X-ray and optical data, we find that the X-ray and radio measurements are correlated on all time-scales from seconds to one day. Correlation with the optical flux densities is weak at short time-scales, but becomes significant on time-scales greater than a few hours. We evaluate the physical conditions (size, magnetic field, and internal energy) associated with 86 individual radio flares, which in turn allows us to place a lower limit on the kinetic feedback over the 15 d of intense activity. If this energy was deposited locally to the source, as implied by the failure to detect jets on angular scales larger than milliarcsec, then we predict that a nova-like shell could have been formed. [ABSTRACT FROM AUTHOR]

All 280 of the statistically complete Palomar sample of nearby (<120 Mpc) galaxies δ > 20° have been observed at 1.5 GHz as part of the LeMMINGs e -MERLIN legacy survey. Here, we present Chandra X-ray observations of the nuclei of 213 of these galaxies, including a statistically complete sub-set of 113 galaxies in the declination range 40° <δ < 65°. We observed galaxies of all optical spectral types, including 'active' galaxies [e.g. low-ionization nuclear emission line regions (LINERs) and Seyferts] and 'inactive' galaxies like |${\rm H\, \small {II}}$| galaxies and absorption line galaxies (ALG). The X-ray flux limit of our survey is 1.65 × 10−14 erg s−1 cm−2 (0.3−10 keV). We detect X-ray emission coincident within 2 arcsec of the nucleus in 150/213 galaxies, including 13/14 Seyferts, 68/77 LINERs, 13/22 ALGs and 56/100 |${\rm H\, \small {II}}$| galaxies, but cannot completely rule out contamination from non-AGN processes in sources with nuclear luminosities |$\lesssim 10^{39}$|  erg s−1. We construct an X-ray Luminosity function (XLF) and find that the local galaxy XLF, when including all active galactic nucleus (AGN) types, can be represented as a single power law of slope −0.54 ± 0.06. The Eddington ratio of the Seyferts is usually 2−4 decades higher than that of the LINERs, ALGs, and |${\rm H\, \small {II}}$| galaxies, which are mostly detected with Eddington ratios |$\lesssim 10^{-3}$|⁠. Using [ |${\rm O\, \small {III}}$| ] line measurements and black hole masses from the literature, we show that LINERs, |${\rm H\, \small {II}}$| galaxies and ALGs follow similar correlations to low luminosities, suggesting that some 'inactive' galaxies may harbour AGN. [ABSTRACT FROM AUTHOR]

What determines the nuclear radio emission in local galaxies? To address this question, 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 [H  ii and absorption line galaxies (ALGs)] galaxies. Using [O  iii ] luminosity (⁠|$L_{\rm [O\, \small {III}]}$|⁠) 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 core) is found to scale with BH mass (M BH) and [O  iii ] luminosity. Below M BH ∼ 106.5 M⊙, stellar processes from non-jetted H  ii galaxies dominate with |$L_{\rm core} \propto M_{\rm BH}^{0.61\pm 0.33}$| and |$L_{\rm core} \propto L_{\rm [O\, \small {III}]}^{0.79\pm 0.30}$|⁠. Above M BH ∼ 106.5 M⊙, accretion-driven processes dominate with |$L_{\rm core} \propto M_{\rm BH}^{1.5-1.65}$| and |$L_{\rm core} \propto L_{\rm [O\, \small {III}]}^{0.99-1.31}$| for active galaxies: radio-quiet/loud LINERs, Seyferts, and jetted H  ii 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 BH ≳ 107 M⊙, 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 H  ii galaxies may host weakly active BHs. Fuel-starved BHs and recurrent activity account for ALG properties. In conclusion, specific accretion–ejection states of active BHs determine the radio production and the optical classification of local active galaxies. [ABSTRACT FROM AUTHOR]

We present an overview and description of the e -MERGE Survey (e -MERLIN Galaxy Evolution Survey) Data Release 1 (DR1), a large program of high-resolution 1.5-GHz radio observations of the GOODS-N field comprising ∼140 h of observations with enhanced-Multi-Element Remotely Linked Interferometer Network (e -MERLIN) and ∼40 h with the Very Large Array (VLA). We combine the long baselines of e -MERLIN (providing high angular resolution) with the relatively closely packed antennas of the VLA (providing excellent surface brightness sensitivity) to produce a deep 1.5-GHz radio survey with the sensitivity (⁠|${\sim}1.5\, \mu$|  Jy beam−1), angular resolution (0.2–0.7 arcsec) and field-of-view (∼15 × 15 arcmin2) to detect and spatially resolve star-forming galaxies and active galactic nucleus (AGN) at |$z$| ≳ 1. The goal of e -MERGE is to provide new constraints on the deep, sub-arcsecond radio sky which will be surveyed by SKA1-mid. In this initial publication, we discuss our data analysis techniques, including steps taken to model in-beam source variability over an ∼20-yr baseline and the development of new point spread function/primary beam models to seamlessly merge e -MERLIN and VLA data in the uv plane. We present early science results, including measurements of the luminosities and/or linear sizes of ∼500 galaxies selected at 1.5 GHz. In combination with deep Hubble Space Telescope observations, we measure a mean radio-to-optical size ratio of r e-MERGE/ r HST ∼ 1.02 ± 0.03, suggesting that in most high-redshift galaxies, the ∼GHz continuum emission traces the stellar light seen in optical imaging. This is the first in a series of papers that will explore the ∼kpc-scale radio properties of star-forming galaxies and AGN in the GOODS-N field observed by e -MERGE DR1. [ABSTRACT FROM AUTHOR]

Context. The occurrence of active galactic nuclei (AGN) is critical to our understanding of galaxy evolution and formation. Radio observations provide a crucial, dust-independent tool to study the role of AGN. However, conventional radio surveys of deep fields ordinarily have arc-second scale resolutions often insufficient to reliably separate radio emission in distant galaxies originating from star-formation and AGN-related activity. Very long baseline interferometry (VLBI) can offer a solution by identifying only the most compact radio emitting regions in galaxies at cosmological distances where the high brightness temperatures (in excess of 105 K) can only be reliably attributed to AGN activity. Aims. We present the first in a series of papers exploring the faint compact radio population using a new wide-field VLBI survey of the GOODS-N field. This will expand upon previous surveys, permitting the characterisation of the faint, compact radio source population in the GOODS-N field. The unparalleled sensitivity of the European VLBI Network (EVN) will probe a luminosity range rarely seen in deep wide-field VLBI observations, thus providing insights into the role of AGN to radio luminosities of the order 1022 WHz−1 across cosmic time. Methods. The newest VLBI techniques are used to completely cover an entire 7′̣5 radius area to milliarcsecond resolutions, while bright radio sources (S > 0.1 mJy) are targeted up to 25′ from the pointing centre. Multi-source self-calibration, and a primary beam model for the EVN array are used to correct for residual phase errors and primary beam attenuation respectively. Results. This paper presents the largest catalogue of VLBI detected sources in GOODS-N comprising of 31 compact radio sources across a redshift range of 0.11–3.44, almost three times more than previous VLBI surveys in this field. We provide a machine-readable catalogue and introduce the radio properties of the detected sources using complementary data from the e-MERLIN Galaxy Evolution survey (eMERGE). [ABSTRACT FROM AUTHOR]

Context. Minor mergers are important processes contributing significantly to how galaxies evolve across the age of the Universe. Their impact on the growth of supermassive black holes and star formation is profound – about half of the star formation activity in the local Universe is the result of minor mergers. Aims. The detailed study of dense molecular gas in galaxies provides an important test of the validity of the relation between star formation rate and HCN luminosity on different galactic scales – from whole galaxies to giant molecular clouds in their molecular gas-rich centers. Methods. We use observations of HCN and HCO+ 1−0 with NOEMA and of CO3−2 with the SMA to study the properties of the dense molecular gas in the Medusa merger (NGC 4194) at 1′′ resolution. In particular, we compare the distribution of these dense gas tracers with CO2−1 high-resolution maps in the Medusa merger. To characterize gas properties, we calculate the brightness temperature ratios between the three tracers and use them in conjunction with a non-local thermodynamic equilibrium (non-LTE) radiative line transfer model. Results. The gas represented by HCN and HCO+ 1−0, and CO3−2 does not occupy the same structures as the less dense gas associated with the lower-J CO emission. Interestingly, the only emission from dense gas is detected in a 200 pc region within the “Eye of the Medusa”, an asymmetric 500 pc off-nuclear concentration of molecular gas. Surprisingly, no HCN or HCO+ is detected for the extended starburst of the Medusa merger. Additionally, there are only small amounts of HCN or HCO+ associated with the active galactic nucleus. The CO3−2/2−1 brightness temperature ratio inside “the Eye” is ~2.5 – the highest ratio found so far – implying optically thin CO emission. The CO2−1/HCN 1−0 (~9.8) and CO2−1/HCO+ 1−0 (~7.9) ratios show that the dense gas filling factor must be relatively high in the central region, consistent with the elevated CO3−1/2−1 ratio. Conclusions. The line ratios reveal an extreme, fragmented molecular cloud population inside the Eye with large bulk temperatures (T > 300 K) and high gas densities (n(H2) > 104 cm-3). This is very different from the cool, self-gravitating structures of giant molecular clouds normally found in the disks of galaxies. The Eye of the Medusa is found at an interface between a large-scale minor axis inflow and the central region of the Medusa. Hence, the extreme conditions inside the Eye may be the result of the radiative and mechanical feedback from a deeply embedded, young and massive super star cluster formed due to the gas pile-up at the intersection. Alternatively, shocks from the inflowing gas entering the central region of the Medusa may be strong enough to shock and fragment the gas. For both scenarios, however, it appears that the HCN and HCO+ dense gas tracers are not probing star formation, but instead a post-starburst and/or shocked ISM that is too hot and fragmented to form newstars. Thus, caution is advised in taking the detection of emission from dense gas tracers as evidence of ongoing or imminent star formation. [ABSTRACT FROM AUTHOR]

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 H  ii 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 1032 to 1040 erg s−1: LINERs and H  ii 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 ∼107 M⊙, but a break emerges at lower masses. Using [O  iii ] line luminosity as a proxy for the accretion luminosity, active nuclei and jetted H  ii 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; H  ii galaxies may host weak active BHs and/or nuclear star-forming cores; and recurrent BH activity may account for ALG properties. [ABSTRACT FROM AUTHOR]

We studied the nearby, interacting galaxy NGC 5195 (M 51b) in the radio, optical and X-ray bands. We mapped the extended, low-surface-brightness features of its radio-continuum emission; determined the energy content of its complex structure of shock-ionized gas; constrained the current activity level of its supermassive nuclear black hole. In particular, we combined data from the European Very Long Baseline Interferometry Network (∼1-pc scale), from our new e-MERLIN observations (∼10-pc scale), and from the Very Large Array (∼100–1000-pc scale), to obtain a global picture of energy injection in this galaxy. We put an upper limit to the luminosity of the (undetected) flat-spectrum radio core. We find steep-spectrum, extended emission within 10 pc of the nuclear position, consistent with optically thin synchrotron emission from nuclear star formation or from an outflow powered by an active galactic nucleus (AGN). A linear spur of radio emission juts out of the nuclear source towards the kpc-scale arcs (detected in radio, Hα and X-ray bands). From the size, shock velocity, and Balmer line luminosity of the kpc-scale bubble, we estimate that it was inflated by a long-term-average mechanical power ∼3–6 × 1041 erg s−1 over the last 3–6 Myr. This is an order of magnitude more power than can be provided by the current level of star formation, and by the current accretion power of the supermassive black hole. We argue that a jet-inflated bubble scenario associated with previous episodes of AGN activity is the most likely explanation for the kpc-scale structures. [ABSTRACT FROM AUTHOR]

We measure the evolution of sizes for star-forming galaxies as seen in 1.4 GHz continuum radio for z  = 0–3. The measurements are based on combined VLA+MERLIN data of the Hubble Deep Field, and using a uv -stacking algorithm combined with model fitting to estimate the average sizes of galaxies. A sample of ∼1000 star-forming galaxies is selected from optical and near-infrared catalogues, with stellar masses M⊙ ≈ 1010–1011 M⊙ and photometric redshifts 0–3. The median sizes are parametrized for stellar mass M * = 5 × 1010 M⊙ as |$R_{\rm e} = A\times {}(H(z)/H(1.5))^{\alpha _z}$|⁠. We find that the median radio sizes evolve towards larger sizes at later times with α z  = −1.1 ± 0.6, and A (the median size at z ≈ 1.5) is found to be |$0. \!\!^{\prime\prime} 26\pm {}0. \!\!^{\prime\prime} 07$| or 2.3±0.6 kpc. The measured radio sizes are typically a factor of 2 smaller than those measure in the optical, and are also smaller than the typical H α sizes in the literature. This indicates that star formation, as traced by the radio continuum, is typically concentrated towards the centre of galaxies, for the sampled redshift range. Furthermore, the discrepancy of measured sizes from different tracers of star formation, indicates the need for models of size evolution to adopt a multiwavelength approach in the measurement of the sizes star-forming regions. [ABSTRACT FROM AUTHOR]

We present a deep survey of the Super-Cluster Assisted Shear Survey (SuperCLASS) supercluster – a region of sky known to contain five Abell clusters at redshift z ∼ 0.2 – performed using the Arcminute Microkelvin Imager (AMI) Large Array (LA) at 15.5 GHz. Our survey covers an area of approximately 0.9 deg2.We achieve a nominal sensitivity of 32.0 μJy beam−1 towards the field centre, finding 80 sources above a 5σ threshold. We derive the radio colour– colour distribution for sources common to three surveys that cover the field and identify three sources with strongly curved spectra – a high-frequency-peaked source and two GHz-peakedspectrum sources. The differential source count (i) agrees well with previous deep radio source counts, (ii) exhibits no evidence of an emerging population of star-forming galaxies, down to a limit of 0.24 mJy, and (iii) disagrees with some models of the 15 GHz source population. However, our source count is in agreement with recent work that provides an analytical correction to the source count from the Square Kilometre Array Design Study (SKADS) Simulated Sky, supporting the suggestion that this discrepancy is caused by an abundance of flat-spectrum galaxy cores as yet not included in source population models. [ABSTRACT FROM AUTHOR]

We present high-sensitivity eMERLIN radio images of the Seyfert galaxy NGC4151 at 1.51 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 yr 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 active galactic nucleus (AGN) that is currently active and feeding the jet. We detect no significant motion in 22 yr between C4 and the component C3, which is unresolved in the eMERLIN image. We present a spectral index image made within the 512MHz band of the 1.51 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 (H α, [OIII] 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 photoionization from the central AGN is responsible for the observed emission-line properties further than 4 arcsec (360 pc) from the core, C4. Within this region, a body of evidence (radio-line co-spatiality, low [O III]/H α and estimated fast shocks) suggests additional ionization from the jet. [ABSTRACT FROM AUTHOR]

We use Atacama Large Millimeter/submillimeter Array (ALMA) observations of H30α (231.90 GHz) emission from the low-metallicity dwarf galaxy NGC5253 to measure the star formation rate (SFR) within the galaxy and to test the reliability of SFRs derived from other commonly used metrics. The H30α emission, which originates mainly from the central starburst, yields a photoionizing photon production rate of (1.9 ± 0.3) × 1052 s-1 and an SFR of 0.087 ± 0.013M☉ yr-1 based on conversions that account for the low metallicity of the galaxy and for stellar rotation. Among the other star formation metrics we examined, the SFR calculated from the total infrared flux was statistically equivalent to the values from the H30α data. The SFR based on a previously published version of the Hα flux that was extinction corrected using Paα and Paβ lines was lower than but also statistically similar to the H30α value. The mid-infrared (22 μm) flux density and the composite star formation tracer based on Hα and mid-infrared emission give SFRs that were significantly higher because the dust emission appears unusually hot compared to typical spiral galaxies. Conversely, the 70 and 160 μm flux densities yielded SFRs lower than the H30α value, although the SFRs from the 70 μm and H30α data were within 1σ-2σ of each other. While further analysis on a broader range of galaxies is needed, these results are instructive of the best and worst methods to use when measuring SFR in low-metallicity dwarf galaxies like NGC5253. [ABSTRACT FROM AUTHOR]

IC 883 is a luminous infrared galaxy (LIRG) classified as a starburst-active galactic nucleus (AGN) composite. In a previous study, we detected a low-luminosity AGN (LLAGN) radio candidate. Here, we report on our radio follow-up at three frequencies that provides direct and unequivocal evidence of the AGN activity in IC 883. Our analysis of archival X-ray data, together with the detection of a transient radio source with luminosity typical of bright supernovae, gives further evidence of the ongoing star formation activity, which dominates the energetics of the system. At sub-parsec scales, the radio nucleus has a core-jet morphology with the jet being a newly ejected component showing a subluminal proper motion of 0.6-1 c. The AGN contributes less than 2 per cent of the total IR luminosity of the system. The corresponding Eddington factor is ~10-3, suggesting this is a low-accretion rate engine, as often found in LLAGNs. However, its high bolometric luminosity (~1044 erg s-1) agrees better with a normal AGN. This apparent discrepancy may just be an indication of the transition nature of the nucleus from a system dominated by star formation, to an AGN-dominated system. The nucleus has a strongly inverted spectrum and a turnover at ~4.4 GHz, thus qualifying as a candidate for the least luminous (L5.0 GHz ~ 6.3 ⨰ 1028 erg s-1 Hz-1) and one of the youngest (~3 ⨰ 103 yr) gigahertz-peaked spectrum (GPS) sources. If the GPS origin for the IC 883 nucleus is confirmed, then advanced mergers in the LIRG category are potentially key environments to unveil the evolution of GPS sources into more powerful radio galaxies. [ABSTRACT FROM AUTHOR]

We present high-resolution e-Multi-Element Radio Linked Interferometer Network radio continuum maps of the dwarf irregular galaxy IC 10 at 1.5 and 5 GHz. We detect 11 compact sources at 1.5 GHz, five of which have complementary detections at 5 GHz. We classify three extended sources as compact HII regions within IC 10, five sources as contaminating background galaxies and identify three sources that require additional observations to classify. We do not expect that any of these three sources are supernova remnants as they will likely be resolved out at the assumed distance of IC 10 (0.7 Mpc). We correct integrated flux densities of IC 10 from the literature for contamination by unrelated background sources and obtain updated flux density measurements of 354±11 mJy at 1.5 GHz and 199 ± 9 mJy at 4.85 GHz. The background contamination does not contribute significantly to the overall radio emission from IC 10, so previous analysis concerning its integrated radio properties remains valid. [ABSTRACT FROM AUTHOR]

We present a radio light curve of supernova (SN) 2014C taken with the Arcminute Microkelvin Imager (AMI) Large Array at 15.7 GHz. Optical observations presented by Milisavljevic et al. demonstrated that SN 2014C metamorphosed from a stripped-envelope Type Ib SN into a strongly interacting Type IIn SN within 1 yr. The AMI light curve clearly shows two distinct radio peaks, the second being a factor of 4 times more luminous than the first peak. This double bump morphology indicates two distinct phases of mass-loss from the progenitor star with the transition between density regimes occurring at 100-200 d. This reinforces the interpretation that SN 2014C exploded in a low-density region before encountering a dense hydrogen-rich shell of circumstellar material that was likely ejected by the progenitor prior to the explosion. The AMI flux measurements of the first light-curve bump are the only reported observations taken within ∼50 to ∼125 d post-explosion, before the blast-wave encountered the hydrogen shell. Simplistic synchrotron self-absorption and free-free absorption modelling suggest that some physical properties of SN 2014C are consistent with the properties of other Type Ibc and IIn SNe. However, our single frequency data does not allow us to distinguish between these two models, which implies that they are likely too simplistic to describe the complex environment surrounding this event. Lastly, we present the precise radio location of SN 2014C obtained with the electronic Multi-Element Remotely Linked Interferometer Network, which will be useful for future very long baseline interferometry observations of the SN. [ABSTRACT FROM AUTHOR]

We present a radio light curve of supernova (SN) 2014C taken with the Arcminute Microkelvin Imager (AMI) Large Array at 15.7 GHz. Optical observations presented by Milisavljevic et al. demonstrated that SN 2014C metamorphosed from a stripped-envelope Type Ib SN into a strongly interacting Type IIn SN within 1 yr. The AMI light curve clearly shows two distinct radio peaks, the second being a factor of 4 times more luminous than the first peak. This double bump morphology indicates two distinct phases of mass-loss from the progenitor star with the transition between density regimes occurring at 100-200 d. This reinforces the interpretation that SN 2014C exploded in a low-density region before encountering a dense hydrogen-rich shell of circumstellar material that was likely ejected by the progenitor prior to the explosion. The AMI flux measurements of the first light-curve bump are the only reported observations taken within ~50 to ~125 d post-explosion, before the blast-wave encountered the hydrogen shell. Simplistic synchrotron self-absorption and free-free absorption modelling suggest that some physical properties of SN 2014C are consistent with the properties of other Type Ibc and IIn SNe. However, our single frequency data does not allow us to distinguish between these two models, which implies that they are likely too simplistic to describe the complex environment surrounding this event. Lastly, we present the precise radio location of SN 2014C obtained with the electronic Multi-Element Remotely Linked Interferometer Network, which will be useful for future very long baseline interferometry observations of the SN. [ABSTRACT FROM AUTHOR]

We present a radio light curve of supernova (SN) 2014C taken with the Arcminute Microkelvin Imager (AMI) Large Array at 15.7 GHz. Optical observations presented by Milisavljevic et al. demonstrated that SN 2014C metamorphosed from a stripped-envelope Type Ib SN into a strongly interacting Type IIn SN within 1 yr. The AMI light curve clearly shows two distinct radio peaks, the second being a factor of 4 times more luminous than the first peak. This double bump morphology indicates two distinct phases of mass-loss from the progenitor star with the transition between density regimes occurring at 100-200 d. This reinforces the interpretation that SN 2014C exploded in a low-density region before encountering a dense hydrogen-rich shell of circumstellar material that was likely ejected by the progenitor prior to the explosion. The AMI flux measurements of the first light-curve bump are the only reported observations taken within ~50 to ~125 d post-explosion, before the blast-wave encountered the hydrogen shell. Simplistic synchrotron self-absorption and free-free absorption modelling suggest that some physical properties of SN 2014C are consistent with the properties of other Type Ibc and IIn SNe. However, our single frequency data does not allow us to distinguish between these two models, which implies that they are likely too simplistic to describe the complex environment surrounding this event. Lastly, we present the precise radio location of SN 2014C obtained with the electronic Multi-Element Remotely Linked Interferometer Network, which will be useful for future very long baseline interferometry observations of the SN. [ABSTRACT FROM AUTHOR]

We present the results of 325 MHz Giant Metrewave Radio Telescope observations of a supercluster field, known to contain five Abell clusters at redshift z ~ 0.2. We achieve a nominal sensitivity of 34 μJy beam-1 towards the phase centre. We compile a catalogue of 3257 sources with flux densities in the range 183μJy-1.5Jy within the entire ~6.5 deg² field of view. Subsequently, we use available survey data at other frequencies to derive the spectral index distribution for a sub-sample of these sources, recovering two distinct populations - a dominant population which exhibit spectral index trends typical of steep-spectrum synchrotron emission, and a smaller population of sources with typically flat or rising spectra. We identify a number of sources with ultrasteep spectra or rising spectra for further analysis, finding two candidate high-redshift radio galaxies and three gigahertz-peaked-spectrum radio sources. Finally, we derive the Euclidean-normalized differential source counts using the catalogue compiled in this work, for sources with flux densities in excess of 223 μJy. Our differential source counts are consistent with both previous observations at this frequency and models of the low-frequency source population. These represent the deepest source counts yet derived at 325 MHz. Our source counts exhibit the well-known flattening at mJy flux densities, consistent with an emerging population of star-forming galaxies; we also find marginal evidence of a downturn at flux densities below 308 μJy, a feature so far only seen at 1.4 GHz. [ABSTRACT FROM AUTHOR]

Classical novae are the most common astrophysical thermonuclear explosions, occurring on the surfaces of white dwarf stars accreting gas from companions in binary star systems. Novae typically expel about 10−4 solar masses of material at velocities exceeding 1,000 kilometres per second. However, the mechanism of mass ejection in novae is poorly understood, and could be dominated by the impulsive flash of thermonuclear energy, prolonged optically thick winds or binary interaction with the nova envelope. Classical novae are now routinely detected at gigaelectronvolt γ-ray wavelengths, suggesting that relativistic particles are accelerated by strong shocks in the ejecta. Here we report high-resolution radio imaging of the γ-ray-emitting nova V959 Mon. We find that its ejecta were shaped by the motion of the binary system: some gas was expelled rapidly along the poles as a wind from the white dwarf, while denser material drifted out along the equatorial plane, propelled by orbital motion. At the interface between the equatorial and polar regions, we observe synchrotron emission indicative of shocks and relativistic particle acceleration, thereby pinpointing the location of γ-ray production. Binary shaping of the nova ejecta and associated internal shocks are expected to be widespread among novae, explaining why many novae are γ-ray emitters. [ABSTRACT FROM AUTHOR]

Studying molecular gas properties in merging galaxies gives us important clues to the onset and evolution of interaction-triggered starbursts. NGC 4194 (the Medusa merger) is particularly interesting to study, since its FIR-to-CO luminosity ratio rivals that of ultraluminous galaxies (ULIRGs), despite its lower luminosity compared to ULIRGs, which indicates a high star formation efficiency (SFE) that is relative to even most spirals and ULIRGs. We study the molecular medium at an angular resolution of 0.65" × 0.52" (~120 × 98 pc) through our observations of 12CO2-1 emission using the Submillimeter Array (SMA). We compare our 12CO2-1 maps with the optical Hubble Space Telescope and high angular resolution radio continuum images to study the relationship between molecular gas and the other components of the starburst region. The molecular gas is tracing the complicated dust lane structure of NGC 4194 with the brightest emission being located in an off-nuclear ring-like structure with ∼320 pc radius, the Eye of the Medusa. The bulk CO emission of the ring is found south of the kinematical center of NGC 4194. The northern tip of the ring is associated with the galaxy nucleus, where the radio continuum has its peak. Large velocity widths associated with the radio nucleus support the notion of NGC 4194 hosting an active galactic nucleus. A prominent, secondary emission maximum in the radio continuum is located inside the molecular ring. This suggests that the morphology of the ring is partially influenced by massive supernova explosions. From the combined evidence, we propose that the Eye of the Medusa contains a shell of swept up material where we identify a number of giant molecular associations. We propose that the Eye may be the site of an efficient starburst of 5-7 M&#9737; yr-1, but it would still constitute only a fraction of the 30-50 M&#9737; yr-1 star formation rate of the Medusa. Furthermore, we find that ~50% of the molecular mass of NGC 4194 is found in extended filamentary-like structures tracing the minor and major axis dust lanes.We suggest that molecular gas is transported along these lanes, providing the central starburst region with fuel. Interestingly, a comparison with locations of super star clusters (SSCs) reveal that the molecular gas and the SSCs are not co-spatial. [ABSTRACT FROM AUTHOR]

This paper presents the results of the 2009–2010 monitoring sessions of the starburst galaxy M82, obtained with the Multi-Element Radio-Linked Interferometer Network (MERLIN) at 5 GHz and e-MERLIN at 6 GHz. Combining several 5 GHz MERLIN epochs to form a map with 33.0 μJy bm−1 noise level, 52 discrete sources, mostly supernova remnants and H ii regions, are identified. These include three objects which were not detected in the 2002 5 GHz MERLIN monitoring session: supernova SN2008iz, the transient source 43.78+59.3, and a new supernova remnant shell. Flux density variations, in the long (1981 to 2010), medium (2002 to 2010) and short (2009 to 2010) term are investigated. We find that flux densities of supernova remnants (SNRs) in M82 stay constant in most of the sample (∼95 per cent), although the distributions of flux density variations show an offset from zero. This is consistent with a slight statistical reduction in flux density of the source distribution. In addition, aside from SN2008iz and the well-known variable source 41.95+57.5, two sources display tentative evidence for short- and medium-term variations over the period 2009–2010. These sources are amongst the most compact SNR in M82. These flux density variations could be due to changes in the circumstellar and interstellar medium in which the shocks travel. [ABSTRACT FROM AUTHOR]

Context. The high star formation rates of luminous infrared galaxies (LIRGs) make them ideal places for core-collapse supernova (CCSN) searches. Massive star formation can often be found in coexistence with an active galactic nucleus (AGN), contributing jointly to the energy source of LIRGs. At radio frequencies, where light is unaffected by 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. Aims. Our study of the LIRG IC883 aims at: (i) investigating the parsec-scale radio structure of the (circum-)nuclear regions of IC883; (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 IC 883; and (iii) further investigating the nature of SN2011hi at NIR wavelengths. Methods. We used the electronic European very long baseline interferometry (VLBI) Network (e-EVN) at 5GHz, and the electronic Multi-Element Remotely Linked Interferometer Network (e-MERLIN) at 6.9 GHz, to observe contemporaneously the LIRG IC883 at high angular-resolution (from tens to hundreds of milliarcsec) and with high sensitivity (<70 μJy), complemented by archival VLBI data at 5GHz and 8.4 GHz. We also used the Gemini North telescope to obtain late-time JHK photometry for SN2011hi. Results. The circumnuclear regions traced by e-MERLIN at 6.9 GHz have an extension of ∼1 kpc, at a position angle of 130°, 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 5 GHz and complementary archival VLBI data at 5 GHz and 8.4 GHz, reveal 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 strongly indicative of ongoing nuclear CCSN activity. Our e-EVN observations also provided upper limits to the radio luminosity of the two SNe in IC883 recently discovered at NIR wavelengths. We refine the classification of SN2011hi as a Type IIP SN according to our latest epoch of Gemini North observations acquired in 2012, in agreement with a low-luminosity radio SN nature. We estimate a CCSN rate lower limit of 1.1+1.3 -0.6 yr-1 for the entire galaxy, based on three nuclear radio SNe and the circumnuclear SNe 2010cu and 2011hi. [ABSTRACT FROM AUTHOR]

ABSTRACT We use the Planck Early Release Compact Source Catalogue combined with Wilkinson Microwave Anisotropy Probe ( WMAP) and other archival measurements to construct continuum spectra of three nearby dusty star-forming galaxies: Messier 82, NGC 253 and NGC 4945. We carry out a least-squares fit to the spectra using a combination of simple synchrotron, free-free and thermal dust models, and look for evidence of anomalous microwave emission (AME). We find that the radio spectra of all three galaxies are consistent with steep spectrum synchrotron emission, with a significant amount of free-free emission required to explain the Planck and WMAP data points in the frequency range 30-150 GHz. This brings the star formation rate based on free-free emission into better agreement with that from the non-thermal emission. We place limits on the presence of AME in these galaxies, finding that it is lower than expectations based on the ratio of far-infrared to AME from the Galaxy. Nevertheless, the shape of the spectrum of NGC 4945 hints at the presence of AME with a peak around 30 GHz. Future Planck data will let us look more closely at these galaxies, as well as to extend the analysis to many more galaxies. [ABSTRACT FROM AUTHOR]

ABSTRACT We present interferometric CO observations of 12 z∼ 2 submillimetre-faint, star-forming radio galaxies (SFRGs) which are thought to be ultraluminous infrared galaxies (ULIRGs) possibly dominated by warmer dust ( Tdust ≳ 40 K) than submillimetre galaxies (SMGs) of similar luminosities. Four other CO-observed SFRGs are included from the literature, and all the observations are taken at the Plateau de Bure Interferometer (PdBI) in the compact configuration. 10 of the 16 SFRGs observed in CO (63 per cent) are detected at >4σ with a mean inferred molecular gas mass of ∼2 × 1010 M⊙. SFRGs trend slightly above the local ULIRG LFIR- L′CO relation. Since SFRGs are about two times fainter in radio luminosity but exhibit similar CO luminosities to SMGs, this suggests SFRGs are slightly more efficient star formers than SMGs at the same redshifts. SFRGs also have a narrow mean CO linewidth, 320 ± 80 km s−1. Many SMGs have similarly narrow CO linewidths, but very broad features (∼900 km s−1) are present in a few SMGs and are absent from SFRGs. SFRGs bridge the gap between properties of very luminous >5 × 1012 L⊙ SMGs and those of local ULIRGs, and are consistent with intermediate-stage major mergers. We suspect that more moderate luminosity SMGs, not yet surveyed in CO, would show similar molecular gas properties to SFRGs. The active galactic nucleus (AGN) fraction of SFRGs is consistent with SMGs and is estimated to be 0.3 ± 0.1, suggesting that SFRGs are observed near the peak phase of star formation activity and not in a later, post-SMG enhanced AGN phase. The excitation analysis of one SFRG is consistent with the CO excitation observed in SMGs [turning over beyond 12CO( J= 4→3)]. This CO survey of SFRGs serves as a pilot project for the much more extensive survey of Herschel and SCUBA-2 selected sources which only partially overlap with SMGs. Better constraints on the CO properties of a diverse high- z ULIRG population are needed from ALMA to determine the evolutionary origin of extreme starbursts, and what role ULIRGs serve in catalyzing the formation of massive stellar systems in the early Universe. [ABSTRACT FROM AUTHOR]

A faint new radio source has been detected in the nuclear region of the starburst galaxy M82 using Multi-Element Radio-Linked Interferometer Network radio observations designed to monitor the flux density evolution of the recent bright supernova SN 2008iz. This new source was initially identified in observations made between 2009 May 1 and 5 but had not been present in observations made 1 week earlier, or in any previous observations of M82. In this Letter, we report the discovery of this new source and monitoring of its evolution over its first 9 months of existence. The true nature of this new source remains unclear, and we discuss whether this source is an unusual and faint supernova, a supermassive black hole associated with the nucleus of M82 or intriguingly the first detection of radio emission from an extragalactic microquasar. [ABSTRACT FROM AUTHOR]

Using the Very Large Array, a series of high-velocity-resolution observations have been made of the M82 starburst at 1.6 GHz. These observations follow up on previous studies of the main line OH maser emission in the central kiloparsec of this starburst region, but with far greater velocity resolution, showing significant velocity structure in some of the maser spots for the first time. A total of 13 masers were detected, including all but one of the previously known sources. While some of these masers are still unresolved in velocity, these new results clearly show velocity structure in spectra from several of the maser regions. Position–velocity plots show good agreement with the distribution of H i including interesting velocity structure on the blueward feature in the west of the starburst which traces the velocity distribution seen in the ionized gas. [ABSTRACT FROM AUTHOR]

We carry out an exploratory weak gravitational lensing analysis on a combined Very Large Array and Multi-Element Radio-Linked Interferometer Network radio data set: a deep ( rms noise) 1.4 GHz image of the Hubble Deep Field-North. We measure the shear estimator distribution at this radio sensitivity for the first time, finding a similar distribution to that of optical shear estimators for Hubble Space Telescope Advanced Camera for Surveys data in this field. We examine the residual systematics in shear estimation for the radio data and give cosmological constraints from radio–optical shear cross-correlation functions. We emphasize the utility of cross-correlating shear estimators from radio and optical data in order to reduce the impact of systematics. Unexpectedly, we find no evidence of correlation between optical and radio intrinsic ellipticities of matched objects; this result improves the properties of optical–radio lensing cross-correlations. We explore the ellipticity distribution of the radio counterparts to optical sources statistically, confirming the lack of correlation; as a result, we suggest a connected statistical approach to radio shear measurements. [ABSTRACT FROM AUTHOR]

Using the IRAM Plateau de Bure Interferometer (PdBI) we have searched for the upper fine structure line of neutral carbon [ ] and towards the submillimetre galaxies (SMGs) GN 20 (SMM J123711.9+622212, ) and GN 20.2 (SMM J123708.8+622202, ). The far-infrared continuum is detected at 8σ significance in GN 20, with a flux density of , while no continuum is detected in GN 20.2. Both sources are statistically undetected in both and lines; we derive line luminosity limits for both C i and CO of . Assuming carbon excitation temperatures of (the galaxies' measured dust temperatures), we infer C i mass limits of (GN 20) and . The derived C i abundance limits are for GN 20 and for GN 20.2, implying that the systems have Milky Way level carbon enrichment ( X[C i]/ X[H2]) or lower, similar to high-redshift carbon-detected systems (at ) but about 50 times less than the carbon enrichment of local starburst galaxies. Observations of GN 20 and GN 20.2 in high-resolution MERLIN+VLA (Multi-Element Radio Linked Interferometer Network+Very Large Array) radio maps of GOODS-N (Great Observatories Origin Deep Survey-North) are used to further constrain the sizes and locations of active regions. We conclude that the physical gas properties of young rapidly evolving systems like GN 20 and GN 20.2 are likely significantly different than starburst/ULIRG (ultraluminous infrared galaxy) environments in the local Universe yet similar to SMGs. Unless gravitationally amplified examples can be found, observations of galaxies like GN 20 will require the order of magnitude increase in sensitivity of the Atacama Large Millimetre Array (ALMA) to constrain their C i and high- J CO content, despite the fact that they are the brightest systems at . [ABSTRACT FROM AUTHOR]

We identify eight radio sources undetected at 850 μm but robustly detected at 70 μm, confirming that they represent ultraluminous infrared galaxies (ULIRGs) with hotter dust temperatures than submillimetre galaxies (SMGs) at similar luminosities and redshifts. These galaxies share many properties with SMGs: ultraviolet spectra consistent with starbursts, high stellar masses and radio luminosities. We can attribute their radio emission to star formation since high-resolution Multi-Element Radio Linked Interferometer Network (MERLIN) radio maps show extended emission regions (with characteristic radii of 2–3 kpc), which are unlikely to be generated by active galactic nucleus (AGN) activity. These observations provide the first direct confirmation of hot, dusty ULIRGs which are missed by current submillimetre surveys. They have significant implications for future observations from the Herschel Space Observatory and Submillimetre Common-User Bolometer Array 2 (SCUBA2), which will select high-redshift luminous galaxies with less selection biases. [ABSTRACT FROM AUTHOR]

We present high spatial resolution Multi-Element Radio-Linked Interferometer Network (MERLIN) 1.4-GHz radio observations of two high-redshift sources, RG J123623 (HDF 147) and RG J123617 (HDF 130), selected as the brightest radio sources from a sample of submillimetre-faint radio galaxies. They have starburst classifications from their rest-frame ultraviolet spectra. However, their radio morphologies are remarkably compact (<80 and <65 mas, respectively), demanding that the radio luminosity be dominated by active galactic nuclei (AGN) rather than starbursts. Near-infrared (IR) imaging [ Hubble Space Telescope Near Infrared Camera and Multi-Object Spectrometer (NICMOS) F160W] shows large-scale sizes ( , diameters ∼12 kpc) and spectral energy distribution (SED) fitting to photometric points (optical through the mid-IR) reveals massive , old (a few Gyr) stellar populations. Both sources have low flux densities at observed 24 μm and are undetected in observed 70 μm and 850 μm, suggesting a low mass of interstellar dust. They are also formally undetected in the ultradeep 2 Ms Chandra data, suggesting that any AGN activity is likely intrinsically weak. We suggest both galaxies have evolved stellar populations, low star formation rates and low accretion rates on to massive black holes whose radio luminosity is weakly beamed (by factors of a few). A cluster-like environment has been identified near HDF 130 by an overdensity of galaxies at , reinforcing the claim that clusters lead to more rapid evolution in galaxy populations. These observations suggest that high-resolution radio (MERLIN) can be a superb diagnostic tool of AGN in the diverse galaxy populations at . [ABSTRACT FROM AUTHOR]

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 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. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the radio-mid-infrared (MIR) correlation at very low flux densities using extremely deep 1.4-GHz subarcsec angular resolution Multi-Element Radio-Linked Interferometer + Very Large Array observations of a field centred upon the Hubble Deep Field-North, in conjunction with Spitzer 24-μm data. From these results, the MIR-radio correlation is extended to the very faint (∼μJy) radio source population. Tentatively, we detect a small deviation from the correlation at the faintest infrared flux densities. We suggest that this small observed change in the gradient of the correlation is the result of a suppression of the MIR emission in faint star-forming galaxies. This deviation potentially has significant implications for using either the MIR or non-thermal radio emission as a star formation tracer of very low luminosity galaxies. [ABSTRACT FROM AUTHOR]

A study of the distribution of OH gas in the central region of the nearby active starburst galaxy M82 has confirmed two previously known bright masers and revealed several new main line masers. Three of these are seen only at 1665 MHz, one is detected only at 1667 MHz, while the rest are detected in both lines. Observations covering both the 1665- and 1667-MHz lines, conducted with both the Very Large Array and the Multi-Element Radio Linked Interferometer Network, have been used to accurately measure the positions and velocities of these features. This has allowed a comparison with catalogued continuum features in the starburst such as H ii regions and supernova remnants (SNRs), as well as known water and satellite line OH masers. Most of the main line masers appear to be associated with known H ii regions although the two detected only at 1665 MHz are seen along the same line of sight as known SNRs. [ABSTRACT FROM AUTHOR]

New observations are reported of J-band spectra (1.04–1.4 μm) of three Seyfert 2 galaxies, Mkn 34, Mkn 78 and NGC 5929. In each case the spectral range includes the near-infrared lines of [Fe ii], [P ii], He i and Paβ. Each Seyfert galaxy has a known radio jet, and we investigate the infrared line ratios of the nuclear and extended regions of each galaxy compared to the radio structure. In Mkn 34 there is a clear indication of an extranuclear region, probably coincident with a shock induced by the radio jet, in which [Fe ii] is considerably enhanced, although the nuclear emission is almost certainly the result of photoionization by the continuum of the active nucleus. Similar effects in extranuclear regions are seen in the other objects, in the case of Mkn 78 confirming recent studies by Ramos Almeida et al. A possible detection of extranuclear [P ii] emission suggests, if real, that photoionization by the active nucleus is the dominant line excitation mechanism over the whole source, including the regions coincident with the radio jet. [ABSTRACT FROM AUTHOR]

A study of the distribution of OH gas in the central region of the nearby active starburst galaxy M82 has confirmed two previously known bright masers and revealed several new main line masers. Three of these are seen only at 1665 MHz, one is detected only at 1667 MHz, while the rest are detected in both lines. Observations covering both the 1665 and 1667 MHz lines, conducted with both the Very Large Array (VLA) and the Multi-Element Radio Linked Interferometer Network (MERLIN), have been used to accurately measure the positions and velocities of these features. This has allowed a comparison with catalogued continuum features in the starburst such as HII regions and supernova remnants, as well as known water and satellite line OH masers. Most of the main line masers appear to be associated with known HII regions although the two detected only at 1665 MHz are seen along the same line of sight as known supernova remnants. [ABSTRACT FROM PUBLISHER]

We present the results of a second epoch of 18-cm global very long baseline interferometry (VLBI) observations, taken on 2001 February 23, of the central kiloparsec of the nearby starburst galaxy Messier 82. These observations further investigate the structural and flux evolution of the most compact radio sources in the central region of M82. The two most compact radio objects in M82 have been investigated . Using this recent epoch of data in comparison with our previous global VLBI observations and two earlier epochs of European VLBI network observations, we measure expansion velocities in the range of for 41.95+575 and 9000–11 000 km s−1 for 43.31+592 using various independent methods. In each case, the measured remnant expansion velocities are significantly larger than the canonical expansion velocity (500 km s−1) of supernova remnants (SNRs) within M82 predicted from theoretical models. In this paper, we discuss the implications of these measured expansion velocities with respect to the high-density environment that the SNRs are expected to reside in within the centre of the M82 starburst. [ABSTRACT FROM AUTHOR]

Using a combination of observations involving the Very Large Array (VLA), MERLIN and global Very Long Baseline Interferometry (VLBI) networks we have made a detailed study of the radio continuum and the neutral hydrogen (H i) kinematics and distribution within the central kiloparsec of the radio galaxy 3C 293. These observations trace the complex jet structure and identify the position of the steeply inverted radio core at 1.3 GHz. Strong H i absorption is detected against the majority of the inner kiloparsec of 3C 293. This absorption is separated into two dynamically different and spatially resolved systems. Against the eastern part of the inner radio jet, narrow H i absorption is detected and shown to have higher optical depths in areas cospatial with a central dust lane. Additionally, this narrow line is shown to follow a velocity gradient of ∼50 km s−1 arcsec−1, consistent with the velocity gradient observed in optical spectroscopy of ionized gas. We conclude that the narrow H i absorption, dust and ionized gas are physically associated and situated several kiloparsecs from the centre of the host galaxy. Against the western jet emission and core component, broad and complex H i absorption is detected. This broad and complex absorption structure is discussed in terms of two possible interpretations for the gas kinematics observed. We explore the possibility that these broad, double absorption spectra are the result of two gas layers at different velocities and distances along these lines of sight. A second plausible explanation for this absorbing structure is that the H i is situated in rotation about the core of this radio galaxy with some velocity dispersion resulting from infall and outflow of gas from the core region. If the latter explanation were correct, then the mass enclosed by the rotating disc would be at least solar masses within a radius of 400 pc. [ABSTRACT FROM AUTHOR]

We present results from new high angular resolution observations of the neutral hydrogen absorption using global VLBI, MERLIN, and VLA observations of the peculiar radio galaxy 3C 293. These results reveal extensive HI absorption against the inner kiloparsec of the radio jet in this source over a wide range of angular scales. In additional to these sub-arcsecond resolution radio observations we also present infrared imaging of the jet.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html [ABSTRACT FROM PUBLISHER]

We present subarcsec angular resolution observations of the neutral gas in the nearby starburst galaxy NGC 520. The central kpc region of NGC 520 contains an area of significantly enhanced star formation. The radio continuum structure of this region resolves into ∼10 continuum components. By comparing the flux densities of the brightest of these components at 1.4 GHz with published 15-GHz data we infer that these components detected at 1.4 and 1.6 GHz are related to the starburst and are most likely to be collections of several supernova remnants within the beam. None of these components is consistent with emission from an active galactic nuclei. Both neutral hydrogen (H i) and hydroxyl (OH) absorption lines are observed against the continuum emission, along with a weak OH maser feature probably related to the star formation activity in this galaxy. Strong H i absorption traces a velocity gradient of 0.5 km s−1 pc−1 across the central kpc of NGC 520. The H i absorption velocity structure is consistent with the velocity gradients observed in both the OH absorption and in CO emission observations. The neutral gas velocity structure observed within the central kpc of NGC 520 is attributed to a kpc-scale ring or disc. It is also noted that the velocity gradients observed for these neutral gas components appear to differ with the velocity gradients observed from optical ionized emission lines. This apparent disagreement is discussed and attributed to the extinction of the optical emission from the actual centre of this source hence implying that optical ionized emission lines are only detected from regions with significantly different radii to those sampled by the observations presented here. [ABSTRACT FROM AUTHOR]

Abstract Neutral hydrogen has been studied on sub-arcsecond scales in two Seyfert galaxies, NGC 7469 and NGC 7674. The 1.4-GHz continuum emission from these sources agree with higher frequency measurements and shows linear, triple source in NGC 7674 and a compact source surrounded by a weak ring of radio emission in NGC 7469. In both of these sources we detect deep localized Hi absorption in front of a single continuum component. In the case of NGC 7674 the Hi absorption is only seen against the central component and has a peak optical depth of 0.21 ± 0.03 , a linewidth of 114 ± 7 km s[sup -1] and a heliocentric velocity of 8623 ± 5 km s[sup -1] . The integrated H i absorption against the central component corresponds to a column density of 5.0 ± 0.7 × 10[sup 21] atom cm[sup -2] . We interpret the lack of H i absorption against the east and west components ( τ < 0.07 and 0.06) as evidence that the H i is localized within the central few hundred pc, similar to the H i observed against the nucleus of NGC 4151, and has an upper mass limit of ∼4 × 10[sup 5] M[sub ⊙] . We speculate that this H i may be associated with a dusty torus. Giant Meterwavelength Radio Telescope (GMRT) results show extended emission and give a rest velocity of 8699 ± 20 km s[sup -1] . The Hi absorption against NGC 7469 shows a single deep feature against the strong central component. The line has a peak optical depth 0.25, a linewidth of 65 ± 6 km s[sup -1] and a heliocentric velocity of 4843 ± 5 km s[sup -1] . The integrated column density is 3.6 ± 0.4 × 10[sup 21] atom cm[sup -2] . Unfortunately the other components in NGC 7469 are too weak to set significant limits to the H i optical depth, and hence, unlike NGC 7674, it is not possible to constrain the size of the absorbing gas. [ABSTRACT FROM AUTHOR]

Nova outbursts take place in binary star systems comprising a white dwarf and either a low-mass Sun-like star or, as in the case of the recurrent nova RS Ophiuchi, a red giant. Although the cause of these outbursts is known to be thermonuclear explosion of matter transferred from the companion onto the surface of the white dwarf, models of the previous (1985) outburst of RS Ophiuchi failed to adequately fit the X-ray evolution and there was controversy over a single-epoch high-resolution radio image, which suggested that the remnant was bipolar rather than spherical as modelled. Here we report the detection of spatially resolved structure in RS Ophiuchi from two weeks after its 12 February 2006 outburst. We track an expanding shock wave as it sweeps through the red giant wind, producing a remnant similar to that of a type II supernova but evolving over months rather than millennia. As in supernova remnants, the radio emission is non-thermal (synchrotron emission), but asymmetries and multiple emission components clearly demonstrate that contrary to the assumptions of spherical symmetry in models of the 1985 explosion, the ejection is jet-like, collimated by the central binary whose orientation on the sky can be determined from these observations. [ABSTRACT FROM AUTHOR]

We report deep EVN and eMERLIN observations of the Type Ia SN 2014J in the nearby galaxy M82. 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 to (for a wind speed of 100 km s–1). If the medium around the supernova is uniform, then nISM ≲ 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 an exploding WD, are ruled out by our observations. (While completing our work, we noticed that a paper by Margutti et al. was submitted to The Astrophysical Journal. From a non-detection of X-ray emission from SN 2014J, the authors obtain limits of M☼ yr–1 (for a wind speed of 100 km s–1) and nISM ≲ 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. 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.) Our estimates on the limits on the gas density surrounding SN2011fe, using the flux density limits from Chomiuk et al., agree well with their results. Although we discuss the possibilities of an SD scenario passing 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. [ABSTRACT FROM AUTHOR]