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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]

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 study intergalactic medium (IGM) heating in a sample of five fossil galaxy groups by using their radio properties at 610 MHz and 1.4 GHz. The power by radio jets introducing mechanical heating for the sampled objects is not sufficient enough to suppress the cooling flow. Therefore, we discussed shock-, vortex heating, and conduction as alternative heating processes. Further, the 1.4 GHz and 610 MHz radio luminosities of fossil groups are compared to a sample of normal galaxy groups of the same brightest group galaxies (BGGs), stellar mass, and total group stellar mass, quantified using the K-band luminosity. It appears that the fossil BGGs are under luminous at 1.4 GHz and 610 MHz for a given BGG stellar mass and luminosity, in comparison to a general population of the groups. In addition, we explore how the bolometric radio luminosity of fossil sample depends on clusters and groups characteristics. Using the HIghest X-ray FLUx Galaxy Cluster Sample (HIFLUGCS) as a control sample we found that the large-scale behaviours of fossil galaxy groups are consistent with their relaxed and virialized nature. [ABSTRACT FROM PUBLISHER]

Context. Understanding the nature of the power-source in luminous infrared galaxies (LIRG) is difficult due to their extreme obscuration. Observations at radio and mm wavelengths can penetrate large columns of dust and gas and provide unique insights into the properties of the compact obscured nuclei of LIRGs. Aims. The aim of this study is to constrain the dynamics, structure, and feeding of the compact nucleus of NGC 4418, and to reveal the nature of the main hidden power-source: starburst or active galactic nucleus (AGN). Methods. We obtained high spatial resolution observations of NGC 4418 at 1.4 and 5 GHz with MERLIN, and at 230 and 270 GHz with the SMA in very extended configuration. We used the continuum morphology and flux density to estimate the size of the emitting region, the star formation rate, and the dust temperature. Emission lines were used to study kinematics through position-velocity diagrams. Molecular emission was studied with population diagrams and by fitting a local thermal equilibrium (LTE) synthetic spectrum. Results. We detect bright 1-mm-line emission from CO, HC3N, HNC, and C34S and 1.4 GHz absorption from HI. The CO 2-1 emission and HI absorption can be fit by two velocity components at 2090 and 2180 km?s-1. We detect vibrationally excited HC3N and HNC, with Tvib ∼ 300 K. Molecular excitation is consistent with a layered temperature structure, with three main components at 80, 160, and 300 K. For the hot component we estimate a source size of less than 5 pc. The nuclear molecular gas surface density of 104M⊚ pc-2 is extremely high and similar to that found in the ultra-luminous infrared galaxy (ULIRG) Arp220. Conclusions. Our observations confirm the presence of a molecular and atomic in-flow, previously suggested by Herschel observations, which is feeding the activity in the center of NGC 4418. Molecular excitation confirms the presence of a very compact, hot dusty core. If a starburst is responsible for the observed IR flux, this has to be at least as extreme as the one in the ULIRG Arp 220, with an age of 3-10 Myr and a star formation rate >10 M⊚ yr-1. If an AGN is present, it must be extremely Compton-thick. [ABSTRACT FROM AUTHOR]

The radio properties of 11 obscured ‘radio-intermediate’ quasars at redshifts have been investigated using the European Very-Long-Baseline-Interferometry Network (EVN) at 1.66 GHz. A sensitivity of was achieved, and in seven out of 11 sources unresolved radio emission was securely detected. The detected radio emission of each source accounts for ∼30–100 per cent of the total source flux density. The physical extent of this emission is ≲150 pc, and the derived properties indicate that this emission originates from an active galactic nucleus (AGN). The missing flux density is difficult to account for by star formation alone, so radio components associated with jets of physical size ≳150 pc and ≲40 kpc are likely to be present in most of the sources. Amongst the observed sample steep, flat, gigahertz-peaked and compact-steep spectrum sources are all present. Hence, as well as extended and compact jets, examples of beamed jets are also inferred, suggesting that in these sources, the obscuration must be due to dust in the host galaxy, rather than the torus invoked by the unified schemes. Comparing the total to core (≲150 pc) radio luminosities of this sample with different types of AGN suggests that this sample of radio-intermediate obscured quasars shows radio properties that are more similar to those of the high-radio-luminosity end of the low-redshift radio-quiet quasar population than those of Fanaroff–Riley type I (FR I) radio galaxies. This conclusion may reflect intrinsic differences, but could be strongly influenced by the increasing effect of inverse-Compton cooling of extended radio jets at high redshift. [ABSTRACT FROM AUTHOR]

We have developed a semi-empirical simulation of the extragalactic radio continuum sky suitable for aiding the design of next generation radio interferometers such as the Square Kilometre Array (SKA). The emphasis is on modelling the large-scale cosmological distribution of radio sources rather than the internal structure of individual galaxies. Here we provide a description of the simulation to accompany the online release of a catalogue of ≃320 million simulated radio sources. The simulation covers a sky area of 20 × 20 deg2– a plausible upper limit to the instantaneous field of view attainable with future (e.g. SKA) aperture array technologies – out to a cosmological redshift of z= 20, and down to flux density limits of 10 nJy at 151, 610 MHz, 1.4, 4.86 and 18 GHz. Five distinct source types are included: radio-quiet active galactic nuclei (AGN), radio-loud AGN of the Fanaroff–Riley type I (FR I) and FR II structural classes, and star-forming galaxies, the latter split into populations of quiescent and starbursting galaxies. In our semi-empirical approach, the simulated sources are drawn from observed (or extrapolated) luminosity functions and grafted on to an underlying dark matter density field with biases which reflect their measured large-scale clustering. A numerical Press–Schechter style filtering of the density field is used to identify and populate clusters of galaxies. For economy of output, radio source structures are constructed from point source and elliptical subcomponents, and for FR I and FR II sources an orientation-based unification and beaming model is used to partition flux between the core and extended lobes and hotspots. The extensive simulation output gives users the flexibility to post-process the catalogues to achieve more complete agreement with observational data in the years ahead. The ultimate aim is for the ‘idealized skies’ generated by this simulation and associated post-processing to be fed to telescope simulators to optimize the design of the SKA itself. [ABSTRACT FROM AUTHOR]

Fossil galaxy groups are energetically and morphologically ideal environments to study the intergalactic medium (IGM) heating, because their inter-galactic gas is undisturbed due to the lack of recent group scale mergers. We study the role of active galactic nuclei (AGN) in heating the IGM in a sample of five fossil galaxy groups by employing properties at 610 MHz and 1.4 GHz. We find that two of the dominant galaxies in fossil groups, ESO 3060170 and RX J1416.4+2315, are associated with the radio lobes. We evaluate the PdV work of the radio lobes and their corresponding heating power and compare to the X-ray emission loss within cooling radius. Our results show that the power due to mechanical heating is not sufficiently high to suppress the cooling. [ABSTRACT FROM PUBLISHER]