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External galaxies often intervene in front of background radio sources such as quasars and radio galaxies. Linear polarization of the background emission is depolarized by Faraday rotation of inhomogeneous magnetized plasma of the intervening galaxies. Exploring the depolarizing intervening galaxies (DINGs) can be a powerful tool to investigate the cosmological evolution of the galactic magnetic field. In this paper, we investigate the effects of DINGs on background radio emission using theoretical DING models. We find that complex structures of galaxy result in complicated depolarization features and Faraday dispersion functions (FDFs), but, for the features of depolarizations and FDFs, the global component of magnetic fields is important. We show the simplest results with ring magnetic field in the galactic disk. We find that the degree of depolarization significantly depends on the inclination angle and the impact parameter of the DING. We found that the larger the standard deviation, the more likely it is that depolarization will occur. The FDF represents the rotation measure (RM) structure within the beam. The FDF exhibits multi-components due mainly to the RM structure within the beam and the fraction of the DING that covers the background emission (the filling factor). The peak Faraday depth of the FDF is different from the beam-averaged RM of the DING. The Monte Carlo simulations indicate that a DING's contribution to the standard deviation of observed RMs follows σRM ∝ 1/(1 + z) k with k ∼ 2.7 and exhibits a steeper redshift dependence than the wavelength squared. DINGs will have a significant impact on RM catalogs created by future survey projects such as the Square Kilometer Array (SKA) and SKA Precursor/Pathfinder. [ABSTRACT FROM AUTHOR]

We present the initial results of our MeerKAT L-band observations of Abell 3376. We achieved higher (5″) angular resolution and better (∼4 μ Jy beam−1) sensitivity compared to the previous observations. Our achieved sensitivity is only a factor of 2 larger than the thermal noise of MeerKAT. Astrometric and flux comparison of discrete compact sources in the field between MeerKAT and the Very Large Array (VLA) indicated that our calibration procedures were successful. We detected West and East relics, and radio galaxies, which have been observed in previous works. With minimal missing flux problem in our MeerKAT observations, we derived the spectral indices of the West relic (−1.22 ± 0.05), East relic (−1.33 ± 0.08) and central radio galaxies (−0.94 ± 0.05). The improved images revealed faint, extending radio arcs for relics, and connection between the East relic and radio galaxies. It is probable that (at least some of) the re-accelerated electrons of the East relic are supplied by the jets of the radio galaxies. No significant diffuse radio emission was found in cluster central part, supporting previous works with a much better upper limit of radio flux of <1.8 × 1023 W Hz−1. [ABSTRACT FROM AUTHOR]

We present an overview of the results obtained from the study of the resolved distribution of molecular gas around eight young ( ≲ 10 6 yr ), peaked-spectrum radio galaxies. Tracing the distribution and kinematics of the gas around these radio sources allows us to trace the interplay between the jets and the surrounding medium. For three of these sources, we present new CO(1-0) observations, obtained with the Northern Extended Millimeter Array (NOEMA) with arcsecond resolution. In two of these targets, we also detected CN lines, both in emission and absorption. Combining the new observations with already published data, we discuss the main results obtained. Although we found that a large fraction of the cold molecular gas was distributed in disc-like rotating structures, in the vast majority of the sources, high turbulence and deviations from purely quiescent gas (including outflows) were observed in the region co-spatial with the radio continuum emission. This suggests the presence of an interaction between radio plasma and cold molecular gas. In particular, we found that newly born and young radio jets, even those with low power i.e., Pjet < 1045 erg s−1), are able to drive massive outflows of cold, molecular gas. The outflows are, however, limited to the sub-kpc regions and likely short lived. On larger scales (a few kpc), we observed cases where the molecular gas appears to avoid the radio lobes and, instead, wraps around them. The results suggest the presence of an evolutionary sequence, which is consistent with previous simulations, where the type of impact of the radio plasma changes as the jet expands, going from a direct jet-cloud interaction able to drive gas outflows on sub-kpc scales to a more gentle pushing aside of the gas, increasing its turbulence and likely limiting its cooling on kpc scales. This effect can be mediated by the cocoon of shocked gas inflated by the jet–cloud interactions. Building larger samples of young and evolved radio sources for observation at a similar depth and spatial resolution to test this scenario is now needed and may be possible thanks to more data becoming available in the growing public archives. [ABSTRACT FROM AUTHOR]

Feedback from both supermassive black holes and massive stars plays a fundamental role in the evolution of galaxies and the inter-galactic medium. In this paper, we use available data to estimate the total amount of kinetic energy and momentum created per co-moving volume element over the history of the universe from three sources: massive stars and supernovae, radiation pressure and winds driven by supermassive black holes, and radio jets driven by supermassive black holes. Kinetic energy and momentum injection from jets peaks at z ≈ 1, while the other two sources peak at z ≈ 2. Massive stars are the dominant global source of momentum injection. For supermassive black holes, we find that the amount of kinetic energy from jets is about an order-of-magnitude larger than that from winds. We also find that the amount of kinetic energy created by massive stars is about 2.5 εstar times that carried by jets (where εstar is the fraction of injected energy not lost to radiative cooling). We discuss the implications of these results for the evolution of galaxies and IGM. Because the ratio of the black hole mass to galaxy mass is a steeply increasing function of mass, we show that the relative importance of black hole feedback to stellar feedback likewise increases with mass. We show that there is a trend in the present-day universe which, in the simplest picture, is consistent with galaxies that have been dominated by black hole feedback being generally quenched, while galaxies that have been dominated by stellar feedback are star-forming. We also note that the amount of kinetic energy carried by jets and winds appears to be sufficient to explain the properties of hot gas in massive halos (>1013 Mʘ). [ABSTRACT FROM AUTHOR]

Active galactic nuclei (AGNs) make up about 35 per cent of the more than 250 sources detected in very high-energy (VHE) gamma rays to date with the imaging atmospheric Cherenkov telescopes. Apart from four nearby radio galaxies and two AGNs of unknown type, all known VHE AGNs are blazars. Knowledge of the cosmological redshift of gamma-ray blazars is key to enabling the study of their intrinsic emission properties, as the interaction between gamma rays and the extragalactic background light (EBL) results in a spectral softening. Therefore, the redshift determination exercise is crucial to indirectly placing tight constraints on the EBL density, and to studying blazar population evolution across cosmic time. Due to the powerful relativistic jets in blazars, most of their host galaxies' spectral features are outshined, and dedicated high signal-to-noise (S/N) spectroscopic observations are required. Deep medium- to high-resolution spectroscopy of 33 gamma-ray blazar optical counterparts was performed with the European Southern Observatory, New Technology Telescope, Keck II telescope, Shane 3-metre telescope, and the Southern African Large Telescope. From the sample, spectra from 25 objects display spectral features or are featureless and have high S/N. The other eight objects have low-quality featureless spectra. We systematically searched for absorption and emission features and estimated, when possible, the fractional host galaxy flux in the measured total flux. Our measurements yielded 14 firm spectroscopic redshifts, ranging from 0.0838 to 0.8125, one tentative redshift, and two lower limits: one at |$z > 0.382$| and the other at z > 0.629. [ABSTRACT FROM AUTHOR]

The goal of this paper is to investigate the flux and spectral index distribution of FR II radio galaxy 4C 14.11. We focused on the distribution of flux and spectral indices over the lobes, as well as in their hot spots. For that purpose, we used publicly available observations of this radio galaxy given at 1450 and 8440 MHz. Particularly, we used Leahy's Atlas of radio-emitting double radio sources, Jodrell Bank Centre for Astrophysics in Manchester, as well as NASA/IPAC Extragalactic Database. We found that the non-thermal (synchrotron) radiation dominates over the areas of the lobes. Distinction between hot spots and rest of the lobes are much smaller in the spectral index than in the flux. We also found that over the inner parts of both lobes, spectral index α is flat in average and significantly higher than 1.2, indicating that 4C 14.11 is old AGN. [ABSTRACT FROM AUTHOR]

Current and upcoming high angular resolution and multifrequency experiments are well poised to explore the rich landscape of secondary cosmic microwave background (CMB) anisotropies. In this context, we compute, for the first time, the power spectrum of CMB fluctuations from a cosmological distribution of evolving lobes of giant radio galaxies. We also explicitly take into account the non-thermal electron distribution, which has important implications for the inference of the CMB angular power spectrum. We calculate the mean global non-thermal y -distortion, 〈 y 〉NT. For observationally reasonable distribution of the jet luminosities in the range of 1045–1047 erg s−1, we find 〈 y 〉NT to be less than 10−5, and hence not violating the cosmic background explorer limit as previously claimed. Using the unique spectral dependence of the non-thermal Sunyaev–Zeldovich (SZ), we show that a detection of 〈 y 〉NT can be within reach at the level of ≳5σ from a future Primordial Inflation Explorer (PIXIE)-like experiment provided we understand the foregrounds precisely. The total non-thermal SZ power spectrum, |$C^{\mathrm{ NT}}_\ell$|⁠ , from the radio lobes peaks at ℓ ∼ 3000 with an amplitude |$\sim 1{{\ \rm per\ cent}}$| of thermal SZ power spectrum from galaxy clusters. A detection of the |$C^{\mathrm{ NT}}_\ell$|⁠ , with a PIXIE-like sensitivity experiment, can lead to ∼5σ constraint on the mass dependence of the jet luminosity with the constraint becoming at least ten times better for the proposed more ambitious CMB-HD survey. This will further lead to the tightest constraint on the central black hole mass-to-host halo mass scaling relations. [ABSTRACT FROM AUTHOR]

We present an analytical model for the evolution of extended active galactic nuclei (AGNs) throughout their full lifecycle, including the initial jet expansion, lobe formation, and eventual remnant phases. A particular focus of our contribution is on the early jet expansion phase, which is traditionally not well captured in analytical models. We implement this model within the Radio AGN in Semi-Analytic Environments (RAiSE) framework, and find that the predicted radio source dynamics are in good agreement with hydrodynamic simulations of both low-powered Fanaroff-Riley Type-I and high-powered Type-II radio lobes. We construct synthetic synchrotron surface brightness images by complementing the original RAiSE model with the magnetic field and shock-acceleration histories of a set of Lagrangian tracer particles taken from an existing hydrodynamic simulation. We show that a single set of particles is sufficient for an accurate description of the dynamics and observable features of Fanaroff-Riley Type-II radio lobes with very different jet parameters and ambient density profile normalizations. Our new model predicts that the lobes of young (≲10 Myr) sources will be both longer and brighter than expected at the same age from existing analytical models, which lack a jet-dominated expansion phase; this finding has important implications for interpretation of radio galaxy observations. The RAiSE code, written in python , is publicly available on github and pypi. [ABSTRACT FROM AUTHOR]

The warm–hot intergalactic medium (warm–hot IGM, or WHIM) pervades the filaments of the Cosmic Web and harbours half of the Universe's baryons. The WHIM's thermodynamic properties are notoriously hard to measure. Here we estimate a galaxy group–WHIM boundary temperature using a new method. In particular, we use a radio image of the giant radio galaxy (giant RG, or GRG) created by NGC 6185, a massive nearby spiral. We analyse this extraordinary object with a Bayesian 3D lobe model and deduce an equipartition pressure P eq = 6 × 10−16 Pa – among the lowest found in RGs yet. Using an X-ray-based statistical conversion for Fanaroff–Riley II RGs, we find a true lobe pressure |$P = 1.5\substack{+1.7\\ -0.4}\times 10^{-15}\ \mathrm{Pa}$|⁠. Cosmic Web reconstructions, group catalogues, and MHD simulations furthermore imply an Mpc–scale IGM density |$1 + \delta _\mathrm{IGM} = 40\substack{+30\\ -10}$|⁠. The buoyantly rising lobes are crushed by the IGM at their inner side, where an approximate balance between IGM and lobe pressure occurs: P IGM ≈ P. The ideal gas law then suggests an IGM temperature |$T_\mathrm{IGM} = 11\substack{+12\\-5} \times 10^6\ \mathrm{K}$|⁠ , or |$k_\mathrm{B}T_\mathrm{IGM} = 0.9\substack{+1.0\\-0.4}\ \mathrm{keV}$|⁠ , at the virial radius – consistent with X-ray-derived temperatures of similarly massive groups. Interestingly, the method is not performing at its limit: in principle, estimates T IGM ∼ 4 × 106 K are already possible – rivalling the lowest X-ray measurements available. The technique's future scope extends from galaxy group outskirts to the WHIM. In conclusion, we demonstrate that observations of GRGs in Cosmic Web filaments are finally sensitive enough to probe the thermodynamics of galaxy groups and beyond. [ABSTRACT FROM AUTHOR]

We observed the core region of the giant radio galaxy GRS J0844+4627 with e-MERLIN at 1.52 and 5.07 GHz. These observations revealed that the apparent single feature at the centre of GRS J0844+4627, as seen by GMRT, consists of two components separated by 2.7 kpc in projection. Follow-up observations at 1.66 GHz using the EVN unveiled the complex morphologies of the two components. In particular, the south-western component identified with the SDSS J084408.85+462744.2 galaxy morphologically resembles a compact symmetric object (CSO) with a projected linear size of 115 pc. If the CSO hypothesis turns out to be correct, then the overall radio structure of GRS J0844+4627 is triple–double. Given that CSOs are considered young objects, GRS J0844+4627 would appear as a recently restarted active galaxy. [ABSTRACT FROM AUTHOR]

Spatially resolved observations of active galactic nuclei (AGN) host galaxies undergoing feedback processes are one of the most relevant avenues through which galactic evolution can be studied, given the long-lasting effects AGN feedback has on gas reservoirs, star formation, and AGN environments at all scales. Within this context, we report results from Very Large Telescope/MUSE integral field optical spectroscopy of TN J1049-1258, one of the most powerful radio sources known, at a redshift of 3.7. We detected extended (∼18 kpc) Ly α emission, spatially aligned with the radio axis, redshifted by 2250 ± 60 km s ^−1 with respect to the host galaxy systemic velocity, and cospatial with UV continuum emission. This Ly α emission could arise from a companion galaxy, although there are arguments against this interpretation. Alternatively, it might correspond to an outflow of ionized gas stemming from the radio galaxy. The outflow would be the highest redshift spatially resolved ionized outflow to date. The enormous amount of energy injected, however, appears to be unable to quench the host galaxy’s prodigious star formation, occurring at a rate of ∼4500 M _⊙ yr ^−1 , estimated using its far-infrared luminosity. Within the field, we also found two companion galaxies at projected distances of ∼25 and ∼60 kpc from the host, which suggests the host galaxy is harbored within a protocluster.

Compact steep spectrum (CSS) radio sources are active galactic nuclei (AGN) that have radio jets propagating only on galactic scales, defined as having projected linear size (LS) of up to 20 kpc. CSS sources are generally hosted by massive early-type galaxies with little ongoing star formation; however, a small fraction are known to have enhanced star formation. Using archival data from the Faint Images of the Radio Sky at Twenty cm survey, the Very Large Array Sky Survey, and the Sloan Digital Sky Survey, we identify a volume-limited sample of 166 CSS sources at z < 0.2 with L _1.4 GHz > 10 ^24 W Hz ^−1 . Comparing the star formation rates and linear sizes of these CSS sources, we find that the ≈14% of CSS sources with specific star formation rates above 0.01 Gyr ^−1 all have LS < 10 kpc. We discuss the possible mechanisms driving this result, concluding that it is likely the excess star formation in these sources occurred in multiple bursts and ceased prior to the AGN jet being triggered.

We measure the local correlation between radio emission and Compton- y signal across two galaxy clusters, Abell 399 and Abell 401, using maps from the Low Frequency Array and the Atacama Cosmology Telescope  +  Planck. These data sets allow us to make the first measurement of this kind at ∼arcmin resolution. We find that the radio brightness scales as F radio ∝  y 1.5 for Abell 401 and F radio ∝  y 2.8 for Abell 399. Furthermore, using XMM–Newton data, we derive a sublinear correlation between radio and X-ray brightness for both the clusters (⁠|$F_{\mathrm{radio}} \propto F_{\rm X}^{0.7}$|⁠). Finally, we correlate the Compton- y and X-ray data, finding that an isothermal model is consistent with the cluster profiles, |$y \propto F_{\rm X}^{0.5}$|⁠. By adopting an isothermal–β model, we are able, for the first time, to jointly use radio, X-ray, and Compton- y data to estimate the scaling index for the magnetic field profile, B (r) ∝  n e(r)η in the injection and re-acceleration scenarios. Applying this model, we find that the combined radio and Compton- y signal exhibits a significantly tighter correlation with the X-ray across the clusters than when the data sets are independently correlated. We find η ∼ 0.6–0.8. These results are consistent with the upper limit we derive for the scaling index of the magnetic field using rotation measure values for two radio galaxies in Abell 401. We also measure the radio, Compton- y , and X-ray correlations in the filament between the clusters but conclude that deeper data are required for a convincing determination of the correlations in the filament. [ABSTRACT FROM AUTHOR]

We conducted a Very Long Baseline Array (VLBA) observation of the low mass active galactic nucleus (AGN) in galaxy NGC 4293 (z  = 0.003). The object is associated with a low-ionization nuclear emission-line region (LINER). Its black hole mass is estimated as ∼105 or |${\sim}10^7 \, \mathrm{M}_\odot$|⁠. The VLBA 1.5 GHz image shows an inverse symmetric structure with two discrete radio blobs separated by an angular distance of ∼120 mas, corresponding to ∼7 parsec. Furthermore, its integrated radio spectrum has a turnover at the frequency of ∼0.44 GHz. Based on the compactness and spectrum, the nuclear radio source in NGC 4293 belongs to a sample of (megahertz) peaked spectrum (PS/MPS) radio sources with compact symmetric morphologies. NGC 4293 has 1.4 GHz radio power of only |${\sim}10^{20}\, \mathrm{W\, Hz^{-1}}$| with the VLBA observation, which is consistent with local AGNs but lower than the current PS samples. One of the two blobs has a steep radio spectrum α = −0.62 ± 0.08 (S ν ∝ ν+α), while the other one has an inverted spectrum α = 0.32 ± 0.10. The VLBA 1.5 GHz luminosity ratio of the two blobs is 3.23 and both blobs show lateral-flowing structures where the hotspots reside at the edge of each radio lobe. This can be explained as jet interactions with dense circumnuclear medium. We estimate the black hole mass of NGC 4293 through the Fundamental Plane of black hole activity, which constrains the black hole mass to be |${\lesssim}10^6\, \mathrm{M}_\odot$|⁠. It supports that the object is a low-mass AGN and a potential candidate for accreting and ejecting IMBHs. [ABSTRACT FROM AUTHOR]

Extragalactic maser sources are unique tools to derive fundamental physical quantities of the host galaxies, e.g, geometry of accretion disks around super-massive black holes and precise black hole masses, and study in detail the interaction region of nuclear jets/outflows with the interstellar medium, in nearby and distant Active Galactic Nuclei. So far, however, extragalactic maser searches have yielded detection of few percent, and only relatively few maser sources have been found. Because of their unprecedented sensitivity, new upcoming facilities, like the SKA and the ngVLA, will allow to significantly increase the number of known (water) maser sources. This will lead to the chance of performing statistically-relevant studies of the maser phenomenon (and its occurrence), derive extragalactic masers luminosity functions, and ultimately (in particular, through the aid of longer-baselines arrays options) to perform the studies described above for larger samples and up to cosmological distances. [ABSTRACT FROM AUTHOR]

One of the major science goals of square kilometre array (SKA) is to understand the role played by atomic hydrogen (Hi) gas in the evolution of galaxies throughout cosmic time. The hyperfine transition line of the hydrogen atom at 21-cm is one of the best tools to detect and study the properties of Hi gas associated with galaxies. In this paper, we review our current understanding of Hi gas and its relationship with galaxies through observations of the 21-cm line both in emission and absorption. In addition, we provide an overview of the Hi science that will be possible with SKA and its precursors and pathfinders, i.e., Hi 21-cm emission and absorption studies of galaxies from nearby to high redshifts that will trace various processes governing galaxy evolution. [ABSTRACT FROM AUTHOR]

The evolution of the gravitational potentials on large scales due to the accelerated expansion of the Universe is an important and independent probe of dark energy, known as the integrated Sachs–Wolfe (ISW) effect. We measure this ISW effect through cross-correlating the cosmic microwave background maps from the Planck satellite with a radio continuum galaxy distribution map from the recent Rapid ASKAP Continuum Survey (RACS). We detect a positive cross-correlation at |$\sim 2.8\, \sigma$| relative to the null hypothesis of no correlation. We parametrize the strength of the ISW effect through an amplitude parameter and find the constraints to be |$A_{\mathrm{ISW}} = 0.94^{+0.42}_{-0.41}$|⁠, which is consistent with the prediction of an accelerating universe within the current concordance cosmological model, ΛCDM. The credible interval on this parameter is independent of the different bias models and redshift distributions that were considered when marginalizing over the nuisance parameters. We also detect a power excess in the galaxy autocorrelation angular power spectrum on large scales (ℓ ≤ 40), and investigate possible systematic causes. [ABSTRACT FROM AUTHOR]

We present a multifrequency analysis of the radio galaxy 3CR 196.1 (z =0.198), associated with the brightest galaxy of the cool-core cluster CIZAJ0815.4-0303. This nearby radio galaxy shows a hybrid radio morphology and an X-ray cavity, all signatures of a turbulent past activity, potentially due to merger events and active galactic nuclei (AGN) outbursts. We present results of the comparison between Chandra and Very Large Telescope Multi-Unit Spectroscopic Explorer data for the inner region of the galaxy cluster, on a scale of tens of kpc. We discovered H α + [N ii ] λ 6584 emission spatially associated with the X-ray cavity (at ∼10 kpc from the galaxy nucleus) instead of with its rim. This result differs from previous discoveries of ionized gas surrounding X-ray cavities in other radio galaxies harbored in galaxy clusters and could represent the first reported case of ionized gas filling an X-ray cavity, either due to different AGN outbursts or to the cooling of warm (104 < T ≤ 107 K) AGN outflows. We also found that the H α, [N ii ] λ λ 6548, 6584, and [S ii ] λ λ 6718, 6733 emission lines show an additional redward component, at ∼1000 km s−1 from rest frame, with no detection in H β or [O iii ] λ λ 4960, 5008. We believe the most likely explanation for this redward component is the presence of a background gas cloud as there appears to be a discrete difference of velocities between this component and the rest frame. [ABSTRACT FROM AUTHOR]

The cessation of AGN activity in radio galaxies leads to a remnant phase during which jets are no longer sustained, but lobes can be detected for a period of time before they fade away due to radiative and dynamical energy losses. The time-scale of the remnant phase and AGN duty cycle are vital to understand the evolution of radio galaxies. In this paper, we report new band-3 observations with the upgraded Giant Meterwave Radio Telescope (uGMRT) for five remnant radio galaxies. Our uGMRT observations reveal emission of low-surface-brightness in all five remnants with 400 MHz surface brightness in the range of 36–201 mJy arcmin - 2 . With band-3 uGMRT observations, we discover wing-shaped radio morphology in one of our sample sources. Using radio observations at 150, 325, 400 MHz and 1.5 GHz, we model the radio spectral energy distributions (SEDs) of our sample sources with the continuous injection-off (CI OFF ) model, that assumes an active phase with continuous injection followed by a remnant phase. We obtain total source ages ( t s ) in the range of 20.3–41.4 Myr with t OFF / t s distributed in the range of 0.16–0.63, which in turn suggests that they belong to different evolutionary phases. We note that when compared to the remnants reported in the literature, our sample sources tend to show lower spectral ages that can be explained by the combined effects of more dominant inverse Compton losses for our sources present at the relatively higher redshifts and possible rapid expansion of lobes in their less dense environments. [ABSTRACT FROM AUTHOR]

This article gives a brief historical introduction and reviews our current understanding of jets in radio galaxies and quasars from an observational perspective, with an emphasis on observations at radio wavelengths. Recent results on the Fanaroff–Riley (FR) classification scheme, and the nature of radio structures and jets in the FR classes as well as in high-excitation and low-excitation radio galaxies are summarized. The collimation and propagation of jets from nuclear sub-pc to hundreds of kpc scales from both observational and theoretical works have been discussed. The jets exhibit evidence of interaction with a clumpy interstellar medium, especially in young radio sources, and could trigger both star formation as well as suppress star formation depending on the physical conditions. Observational evidence for such interactions and jet feedback which have profound implications our understanding of galaxy evolution have been presented. Recurrent jet activity which has been seen over a wide range of projected linear size and time scales has been discussed. This review article concludes with a brief discussion of unresolved questions on jets which new telescopes should help address. [ABSTRACT FROM AUTHOR]

We report on the galaxy density environment around a high- z radio galaxy (HzRG) at z = 4.72, HSC J083913.17+011308.1 (HSC J0839+0113), probed using an r -dropout Lyman break galaxy (LBG) sample from the Hyper Suprime-Cam Subaru Strategic Program data. We find that HSC J0839+0113 resides in the outskirts of an overdense region identified by the r -dropout galaxies at a 4.7σ significance level. The projected distance between HSC J0839+0113 and the peak position of the overdense region is 0.4 physical Mpc, which is shorter than the typical protocluster radius in this epoch. According to the extended Press–Schechter and the light cone models, the HSC J0839+0113-hosted overdense region is expected to evolve into a halo >1014  |${M_{\odot}}$| at z = 0 with a high probability of |$>\!\! 80\%$|⁠. These findings suggest that HSC J0839+0113 is associated with a protocluster. The HSC J0839+0113 rich-system is the most overdense region of LBGs among the known protoclusters with LBGs in the same cosmic epoch. [ABSTRACT FROM AUTHOR]

The features of estimating the energies of the magnetic field and relativistic electrons of synchrotron radio sources, the X-ray emission of which is produced by the invers Compton scattering of synchrotron photons (the synchrotron self-Compton process), are considered. Estimates of these physical parameters depend on the angular dimensions of the radiation sources. The effect of angular dimensions on the estimates of physical parameters is illustrated by an estimate of the magnetic induction of the hot spot A of the radio galaxy Cygnus A. We showed why it is impossible to use apparent angular dimensions of non-uniform radio sources for estimating their physical parameters. To obtain correct estimates of the energies of the field and particles, we need to use the angular size from the spherical model of the source under study, the spectrum of which coincides with the radio spectrum of the object under study. Taking such an angular size of the source, we obtain the same estimates of the physical parameters of this object, both from radio and X-ray observations. [ABSTRACT FROM AUTHOR]

We present an observational multiwavelength campaign during 2018–19 for PBC J2333.9–2343, a giant radio galaxy with a bright central core associated to a blazar nucleus, whose structure could be due to a significant jet reorientation. We report flux increases by a factor of two or more on timescales shorter than a month, resembling flaring events. The cross correlation between the NIR and optical bands shows quasi-simultaneous variations arising from the jet. The optical variability properties of PBC J2333.9–2343 are more comparable to a sample of blazars than to non-blazar AGN. The SED of the nucleus shows two peaks, with a derived jet angle of 3 degrees, also typical of a blazar. Therefore, we confirm the presence of a blazar-like core in the center of this galaxy. [ABSTRACT FROM AUTHOR]

In this work, we investigate the formation and early evolution phase of X-shaped radio galaxies using the Back-flow model. We show how the X-like winged morphology evolves over time in a tri-axial ambient medium, naturally. At this early stage of formation, we demonstrated that both the pair of jet lobes are actively pushing the ambient material out of their path of propagation, forming (X-ray) cavities that are surrounded by a shocked shell (X-ray bright rims) of swept materials. We also noticed how turbulent the wing is in comparison to the active lobe, generating sites of random shocks, indicating that the wings are not passively evolving structures. This study demonstrated that the ambiguous morphology observed in jets is also imprinted over the ambient medium, providing an alternative perspective in understanding the underlying physical process causing such ambiguities. Finally, we indicate that shearing instabilities cause mixing of ambient material at the shearing interface. [ABSTRACT FROM AUTHOR]

Radio relics are Mpc-sized synchrotron sources located in the peripheral regions of galaxy clusters. Models based on the diffuse shock acceleration (DSA) scenario have been widely accepted to explain the formation of radio relics. However, a critical challenge to these models is that most observed shocks seem too weak to generate detectable emission, unless fossil electrons, a population of mildly energetic electrons that have been accelerated previously, are included in the models. To address this issue, we present a new semi-analytical model to describe the formation and evolution of radio relics by incorporating fossil relativistic electrons into DSA theory, which is constrained by a sample of 14 observed relics, and employ the Press–Schechter formalism to simulate the relics in a 20° × 20° sky field at 50, 158, and 1400 MHz, respectively. Results show that fossil electrons contribute significantly to the radio emission, which can generate radiation four orders of magnitude brighter than that solely produced by thermal electrons at 158 MHz, and the power distribution of our simulated radio relic catalogue can reconcile the observed P 1400– M vir relation. We predict that |$7.1{{\ \rm per\ cent}}$| clusters with |$M_{\mathrm{vir}} \gt 1.2\times 10^{14}\, \mathrm{M}_{\odot }$| would host relics at 158 MHz, which is consistent with the result of |$10 \pm 6{{\ \rm per\ cent}}$| given by the Second Data Release of the LOFAR Two-meter Sky Survey. It is also found that radio relics are expected to cause severe foreground contamination in future epoch of reionization experiments, similar to that of radio haloes. The possibility of active galactic nuclei (AGNs) providing seed fossil relativistic electrons is evaluated by calculating the number of radio-loud AGNs that a shock is expected to encounter during its propagation. [ABSTRACT FROM AUTHOR]

Asymmetry in the spatially integrated, 1D H  i global profiles of galaxies can inform us on both internal (e.g. outflows) and external (e.g. mergers, tidal interactions, and ram pressure stripping) processes that shape galaxy evolution. Understanding which of these primarily drive H  i profile asymmetry is of particular interest. In the lead-up to SKA pathfinder and SKA H  i emission surveys, hydrodynamical simulations have proved to be a useful resource for such studies. Here, we present the methodology behind, as well as first results, of ASymba: Asymmetries in H  i of Simba galaxies, the first time this simulation suite has been used for this type of study. We generate mock observations of the H  i content of these galaxies and calculate the profile asymmetries using three different methods. We find that |$M_{\rm H\, {\small I}}$| has the strongest correlation with all asymmetry measures, with weaker correlations also found with the number of mergers a galaxy has undergone, and gas and galaxy rotation. We also find good agreement with the xGASS sample, in which galaxies with highly asymmetric profiles tend to have lower H  i gas fractions than galaxies with symmetric profiles, and additionally find the same holds in sSFR parameter space. For low H  i mass galaxies, it is difficult to distinguish between asymmetric and symmetric galaxies, but this becomes achievable in the high H  i mass population. These results showcase the potential of ASymba and provide the groundwork for further studies, including comparison to upcoming large H  i emission surveys. [ABSTRACT FROM AUTHOR]

Aims. We present the X-ray imaging and spectral analysis of the diffuse emission around the radio galaxy J1140-2629 (the Spiderweb galaxy) at z = 2.16 and of its nuclear emission, based on a deep (700 ks) Chandra observation. Methods. We obtained a robust characterization of the unresolved nuclear emission, and carefully computed the contamination in the surrounding regions due to the wings of the instrument point spread function. Then, we quantified the extended emission within a radius of 12 arcsec. We used the Jansky Very Large Array radio image to identify the regions overlapping the jets, and performed X-ray spectral analysis separately in the jet regions and in the complementary area. Results. We find that the Spiderweb galaxy hosts a mildly absorbed quasar, showing a modest yet significant spectral and flux variability on a timescale of ∼1 year (observed frame). We find that the emission in the jet regions is well described by a power law with a spectral index of Γ ∼ 2 − 2.5, and it is consistent with inverse-Compton upscattering of the cosmic microwave background photons by the relativistic electrons. We also find a roughly symmetric, diffuse emission within a radius of ∼100 kpc centered on the Spiderweb galaxy. This emission, which is not associated with the jets, is significantly softer and consistent with thermal bremsstrahlung from a hot intracluster medium (ICM) with a temperature of kT = 2.0−0.4+0.7 k T = 2. 0 − 0.4 + 0.7 $ kT = 2.0_{-0.4}^{+0.7} $ keV, and a metallicity of Z <  1.6 Z⊙ at 1σ c.l. The average electron density within 100 kpc is ne = (1.51  ±  0.24 ± 0.14) × 10−2 cm−3, corresponding to an upper limit for the total ICM mass of ≤(1.76  ±  0.30  ±  0.17) × 1012 M⊙ (where error bars are 1σ statistical and systematic, respectively). The rest-frame luminosity L0.5 − 10 keV = (2.0 ± 0.5) × 1044 erg s−1 is about a factor of 2 higher than the extrapolated L − T relation for massive clusters, but still consistent within the scatter. If we apply hydrostatic equilibrium to the ICM, we measure a total gravitational mass M(<100 kpc) = (1.5−0.3+0.5) × 1013 M⊙ M (< 100 kpc) = (1. 5 − 0.3 + 0.5) × 10 13 M ⊙ $ M({ and, extrapolating at larger radii, we estimate a total mass M500 = (3.2−0.6+1.1) × 1013 M⊙ M 500 = (3. 2 − 0.6 + 1.1) × 10 13 M ⊙ $ M_{500} = (3.2^{+1.1}_{-0.6})\times 10^{13}\, M_\odot $ within a radius of r500 = (220 ± 30) kpc. Conclusions. We conclude that the Spiderweb protocluster shows significant diffuse emission within a radius of 12 arcsec, whose major contribution is provided by inverse-Compton scattering associated with the radio jets. Outside the jet regions, we also identified thermal emission within a radius of ∼100 kpc, revealing the presence of hot, diffuse baryons that may represent the embryonic virialized halo of the forming cluster. [ABSTRACT FROM AUTHOR]

Context. Radio-loud active galactic nuclei (AGNs) are thought to possess various sites of particle acceleration, which gives rise to the observed nonthermal spectra. Stochastic turbulent acceleration (STA) and diffusive shock acceleration (DSA) are commonly cited as potential sources of high-energy particles in weakly magnetized environments. Together, these acceleration processes and various radiative losses determine the emission characteristics of these extragalactic radio sources. Aims. The purpose of this research is to investigate the dynamical interplay between the STA and DSA in the radio lobes of FR-II radio galaxies, as well as the manner in which these acceleration mechanisms, along with a variety of radiative losses, collectively shape the emission features seen in these extragalactic sources. Methods. A phenomenologically motivated model of STA is considered and subsequently employed on a magnetohydrodynamically simulated radio lobe through a novel hybrid Eulerian-Lagrangian framework. Results. STA gives rise to a curved particle spectrum that is morphologically different from the usual shock-accelerated spectrum. As a consequence of this structural difference in the underlying particle energy spectrum, various multiwavelength features arise in the spectral energy distribution of the radio lobe. Additionally, we observe enhanced diffuse X-ray emission from radio lobes for cases where STA is taken into account in addition to DSA. [ABSTRACT FROM AUTHOR]

With the rapid increase of fast radio burst (FRB) detections within the past few years, there is now a catalogue being developed for all-sky extragalactic dispersion measure (DM) observations in addition to the existing collection of all-sky extragalactic Faraday rotation measurements (RMs) of radio galaxies. We present a method of reconstructing all-sky information of the Galactic magnetic field component parallel to the line of sight, B ∥, using simulated observations of the RM and DM along lines of sight to radio galaxies and FRB populations, respectively. This technique is capable of distinguishing between different input Galactic magnetic fields and thermal electron density models. Significant extragalactic contributions to the DM are the predominant impediment in accurately reconstructing the Galactic DM and 〈 B ∥〉 skies. We look at ways to improve the reconstruction by applying a filtering algorithm on the simulated DM lines of sight and we derive generalized corrections for DM observations at | b | > 10° that help to disentangle Galactic and extragalactic DM contributions. Overall, we are able to reconstruct both large-scale Galactic structure and local features in the Milky Way's magnetic field from the assumed models. We discuss the application of this technique to future FRB observations and address possible differences between our simulated model and observed data, namely: adjusting the priors of the inference model, an unevenly distributed population of FRBs on the sky, and localized extragalactic DM structures. [ABSTRACT FROM AUTHOR]

New-generation radio telescopes like LOFAR are conducting extensive sky surveys, detecting millions of sources. To maximize the scientific value of these surveys, radio source components must be properly associated into physical sources before being cross-matched with their optical/infrared counterparts. In this paper, we use machine learning to identify those radio sources for which either source association is required or statistical cross-matching to optical/infrared catalogues is unreliable. We train a binary classifier using manual annotations from the LOFAR Two-metre Sky Survey (LoTSS). We find that, compared to a classification model based on just the radio source parameters, the addition of features of the nearest-neighbour radio sources, the potential optical host galaxy, and the radio source composition in terms of Gaussian components, all improve model performance. Our best model, a gradient boosting classifier, achieves an accuracy of 95 per cent on a balanced data set and 96 per cent on the whole (unbalanced) sample after optimizing the classification threshold. Unsurprisingly, the classifier performs best on small, unresolved radio sources, reaching almost 99 per cent accuracy for sources smaller than 15 arcsec, but still achieves 70 per cent accuracy on resolved sources. It flags 68 per cent more sources than required as needing visual inspection, but this is still fewer than the manually developed decision tree used in LoTSS, while also having a lower rate of wrongly accepted sources for statistical analysis. The results have an immediate practical application for cross-matching the next LoTSS data releases and can be generalized to other radio surveys. [ABSTRACT FROM AUTHOR]

The discovery of faint Fanaroff–Riley type I (FR I) radio jets in the elliptical galaxy NGC 5322 is reported here using the 144-MHz image from Data Release 2 of the Low-Frequency Array (LOFAR) Two-metre Sky Survey (LoTSS). The jets have an angular extent of ∼40 arcmin or a projected physical extent of ∼360 kpc. The faint jets remain well collimated and disappear in the intergalactic medium, without any detected hotspots or radio lobes. The relatively brighter jets, previously detected only up to the ∼21 kpc extent at higher frequencies, are within the optical extent of the galaxy. The jets become faint abruptly outside, where detection is made only in the LOFAR image. The total radio luminosity of the galaxy at 144 MHz is estimated to be (3.7 ± 0.4) × 1022 W Hz−1. The 144-MHz radio luminosity of the faint jets outside the optical extent is estimated to be (7.1 ± 2.0) × 1021 W Hz−1. The size of the jets is exceptionally large for the galaxy's low radio luminosity, when compared with other radio galaxies. It makes NGC 5322 a rare radio galaxy, previously not detected in other radio surveys. A combined effect of stellar core depletion and low-density environment around the jets, which results in a weak entrainment of the material surrounding the jets, could be responsible for its large size despite a low radio luminosity. [ABSTRACT FROM AUTHOR]

Jet re-orientation associated with the time evolution of radio quasars explains the formation of X-shaped radio galaxies and their preference for isolated environments. But since X-shaped radio galaxies are generally not found in dense environments (e.g., groups/clusters), the jet re-orientation phenomenon for radio galaxies in groups and clusters has been ignored. We take a closer look at the re-orientation of FRI jets with respect to FRII jets, and find that it may constitute the as-yet unidentified trigger for star formation suppression in radio galaxies. We show how the recently explored radio “red geyser” galaxies can be interpreted in this context and ultimately reveal a deeper understanding of why FRII radio galaxies are on one side of the star formation enhancement/suppression divide compared to FRI radio galaxies. [ABSTRACT FROM AUTHOR]

We present neutral atomic hydrogen (H  i) observations using the Robert C. Byrd Green Bank Telescope along the lines of sight to 49 confirmed or possible dwarf satellite galaxies around eight Local Volume systems (M104, M51, NGC 1023, NGC 1156, NGC 2903, NGC 4258, NGC 4565, and NGC 4631). We detect the H  i reservoirs of two candidates (dw0934+2204 and dw1238−1122) and find them to be background sources relative to their nearest foreground host systems. The remaining 47 satellite candidates are not detected in H  i , and we place stringent 5 σ upper limits on their H  i mass. We note that some (15/47) of our non-detections stem from satellites being occluded by their putative host's H  i emission. In addition to these new observations, we compile literature estimates on the H  i mass for an additional 17 satellites. We compare the H  i properties of these satellites to those within the Local Group, finding broad agreement between them. Crucially, these observations probe a 'transition' region between −10 ≳ MV ≳ −14 where we see a mixture of gas-rich and gas-poor satellites. While there are many gas-poor satellites within this region, some are gas-rich and this suggests that the transition towards predominantly gas-rich satellites occurs at LV ∼ 107 L ⊙, in line with simulations. The observations presented here are a key step toward characterizing the properties of dwarf satellite galaxies around Local Volume systems and future wide-field radio surveys with higher angular resolution (e.g. WALLABY) will vastly improve upon the study of such systems. [ABSTRACT FROM AUTHOR]

We present the discovery of highly collimated radio jets spanning a total of 355 kpc around the nearby elliptical galaxy NGC 2663, and the possible first detection of recollimation on kiloparsec scales. The small distance to the galaxy (∼28.5 Mpc) allows us to resolve portions of the jets to examine their structure. We combine multiwavelength data: radio observations by the Murchison Widefield Array (MWA), the Australian Square Kilometre Array Pathfinder (ASKAP) and the Australia Telescope Compact Array (ATCA), and X-ray data from Chandra, Swift , and SRG/eROSITA. We present intensity, rotation measure, polarization, spectral index, and X-ray environment maps. Regions of the southern jet show simultaneous narrowing and brightening, which can be interpreted as a signature of the recollimation of the jet by external, environmental pressure, though it is also consistent with intermittent active galactic nuclei or complex internal jet structure. X-ray data suggest that the environment is extremely poor; if the jet is indeed recollimating, the large recollimation scale (40 kpc) is consistent with a slow jet in a low-density environment. [ABSTRACT FROM AUTHOR]

We investigate the multiwavelength emission from hadronic and leptonic cosmic rays (CRs) in bubbles around galaxies, analogous to the Fermi bubbles of the Milky Way. The bubbles are modelled using 3D magnetohydrodynamical simulations, and are driven by a 0.3 Myr intense explosive outburst from the nucleus of Milky Way-like galaxies. We compute their non-thermal emission properties at different stages throughout their evolution, up to 7 Myr, by post-processing the simulations. We compare the spectral and spatial signatures of bubbles with hadronic, leptonic, and hybrid hadro-leptonic CR compositions. These each show broadly similar emission spectra, comprised of radio synchrotron, inverse Compton, and non-thermal bremsstrahlung components. However, hadronic and hybrid bubbles were found to be brighter than leptonic bubbles in X-rays, and marginally less bright at radio frequencies, and in γ-rays between ∼0.1 and a few 10s of GeV, with a large part of their emission being driven by secondary electrons formed in hadronic interactions. Hadronic systems were also found to be slightly brighter in high-energy γ-rays than their leptonic counterparts, owing to the π0 decay emission that dominates their emission between energies of 100s of GeV and a few TeV. [ABSTRACT FROM AUTHOR]

We study the nature of the faint radio source population detected in the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) Early Science data in the COSMOS field, focusing on the properties of the radio-loud active galactic nuclei (AGNs). Using the extensive multiwavelength data available in the field, we are able to classify 88 per cent of the 5223 radio sources in the field with host galaxy identifications as AGNs (35 per cent) or star-forming galaxies (54 per cent). We select a sample of radio-loud AGNs with redshifts out to z ∼ 6 and radio luminosities 1020 < L1.4 GHz/W Hz−1 < 1027 and classify them as high-excitation and low-excitation radio galaxies (HERGs and LERGs). The classification catalogue is released with this work. We find no significant difference in the host galaxy properties of the HERGs and LERGs in our sample. In contrast to previous work, we find that the HERGs and LERGs have very similar Eddington-scaled accretion rates; in particular we identify a population of very slowly accreting AGNs that are formally classified as HERGs at these low radio luminosities, where separating into HERGs and LERGs possibly becomes redundant. We investigate how black hole mass affects jet power, and find that a black hole mass ≳ 107.8 M⊙ is required to power a jet with mechanical power greater than the radiative luminosity of the AGN (L mech/ L bol > 1). We discuss that both a high black hole mass and black hole spin may be necessary to launch and sustain a dominant radio jet. [ABSTRACT FROM AUTHOR]

We conduct searches for γ-ray emission from the binary black-hole (BBH) mergers reported in the Gravitational-Wave Candidate Event Database (GraceDB). The γ-ray data are from the all-sky survey of the Large-Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope (Fermi), which allows searches for events of given time durations in large sky areas. The Two-Micron All-Sky Survey Photometric Redshift Catalog (2MPZ) is used for target selection, from which galaxy sources within the 90% credible areas and the distance ranges given by the gravitational-wave (GW) detections are determined. Excluding those BBH cases with large credible areas and/or dense fields (containing too many 2MPZ sources), searches for short transient events over the time duration of from −1 to 100 days of a trigger time for seven BBH mergers are conducted. We find two candidate short flaring events in the field of the GW event S200311bg and one in that of S190408an. However, the flaring events all have low significance (after considering the trial factor), and the third one appears off the position of the target galaxy. We discuss one of them from the first field that is detected in different short time-bin data and suggest that it is possibly a real flare arising from a radio galaxy. More such studies for the near-future GW detection run are planned, for which we will adjust our search strategy to be more effective and target flares of various time scales. [ABSTRACT FROM AUTHOR]

We investigate the environmental properties of the z  = 0 radio galaxy population using the simba cosmological hydrodynamic simulation. We identify centrals and satellites from a population of high and low excitation radio galaxies (HERGs and LERGs) in simba , and study their global properties. We find that |$\sim 20{{\ \rm per\ cent}}$| of radio galaxies are satellites, and that there are insignificant differences in the global properties of LERGs based on their central/satellite classification. HERG satellites display lower values of star formation, 1.4 GHz radio luminosity, and Eddington fractions than HERG centrals. We further investigate the environments of radio galaxies and show that HERGs typically live in less dense environments, similar to star-forming galaxies. The environments of high-mass LERGs are similar to non-radio galaxies, but low-mass LERGs live in underdense environments similar to HERGs. LERGs with overmassive black holes reside in the most dense environments, while HERGs with overmassive black holes reside in underdense environments. The richness of a LERG's environment decreases with increasing Eddington fraction, and the environments of all radio galaxies do not depend on radio luminosity for |$\, P_{\rm 1.4~GHz}\lt 10^{24} \rm {~W~Hz}^{-1}$|⁠. Complementing these results, we find that LERGs cluster on the same scale as the total galaxy population, while multiple HERGs are not found within the same dark matter halo. Finally, we show that high density environments support the growth of HERGs rather than LERGs at z  = 2. Simba predicts that with more sensitive surveys, we will find populations of radio galaxies in environments much similar to the total galaxy population. [ABSTRACT FROM AUTHOR]

Identifying active galactic nuclei (AGNs) and isolating their contribution to a galaxy's energy budget is crucial for studying the co-evolution of AGNs and their host galaxies. Brightness temperature (Tb) measurements from high-resolution radio observations at GHz frequencies are widely used to identify AGNs. Here, we investigate using new sub-arcsecond imaging at 144 MHz with the International LOFAR Telescope to identify AGNs using Tb in the Lockman Hole field. We use ancillary data to validate the 940 AGN identifications, finding 83 percent of sources have AGN classifications from SED fitting and/or photometric identifications, yielding 160 new AGN identifications. Considering the multiwavelength classifications, brightness temperature criteria select over half of radio-excess sources, 32 percent of sources classified as radio-quiet AGNs, and 20 percent of sources classified as star-forming galaxies. Infrared colour–colour plots and comparison with what we would expect to detect based on peak brightness in 6 arcsec LOFAR maps imply that the star-forming galaxies and sources at low flux densities have a mixture of star-formation and AGN activity. We separate the radio emission from star-formation and AGN in unresolved, Tb -identified AGNs with no significant radio excess and find the AGN comprises 0.49 ± 0.16 of the radio luminosity. Overall, the non-radio excess AGNs show evidence for having a variety of different radio emission mechanisms, which can provide different pathways for AGNs and galaxy co-evolution. This validation of AGN identification using brightness temperature at low frequencies opens the possibility for securely selecting AGN samples where ancillary data are inadequate. [ABSTRACT FROM AUTHOR]

Broad absorption line quasars (BALQSOs) show strong signatures of powerful outflows, with the potential to alter the cosmic history of their host galaxies. These signatures are only seen in ∼10 per cent of optically selected quasars, although the fraction significantly increases in IR and radio selected samples. A proven physical explanation for this observed fraction has yet to be found, along with a determination of why this fraction increases at radio wavelengths. We present the largest sample of radio matched BALQSOs using the LOFAR Two-metre Sky Survey Data Release 2 and employ it to investigate radio properties of BALQSOs. Within the DR2 footprint, there are 3537 BALQSOs from Sloan Digital Sky Survey DR12 with continuum signal-to-noise ≥5. We find radio-detections for 1108 BALQSOs, with an important subpopulation of 120 LoBALs, an unprecedented sample size for radio matched BALQSOs given the sky coverage to date. BALQSOs are a radio-quiet population that show an increase of ×1.50 radio-detection fraction compared to non-BALQSOs. LoBALs show an increase of ×2.22 that of non-BALQSO quasars. We show that this detection fraction correlates with wind-strength, reddening, and C  iv emission properties of BALQSOs and that these features may be connected, although no single property can fully explain the enhanced radio detection fraction. We create composite spectra for subclasses of BALQSOs based on wind strength and colour, finding differences in the absorption profiles of radio-detected and radio-undetected sources, particularly for LoBALs. Overall, we favour a wind-ISM interaction explanation for the increased radio-detection fraction of BALQSOs. [ABSTRACT FROM AUTHOR]

Peculiar motion of the Solar system, determined from the dipole anisotropy in the Cosmic Microwave Background Radiation (CMBR), has given a velocity 370 km s−1 along RA = 168°, Dec. = −7°. Subsequent peculiar motion determinations from the number counts, sky brightness, or redshift dipoles observed in large samples of distant radio galaxies and quasars yielded peculiar velocities 2 to 10 times larger than CMBR, though in all cases the directions matched with the CMBR dipole. Here, we introduce a novel technique for determining the peculiar motion from the magnitude-redshift (m B– z) Hubble diagram of Type Ia Supernovae (SN Ia), one of the best standard candles available. We find a peculiar velocity 1.6 ± 0.5 × 103 km s−1, larger than the CMBR value roughly by a factor of four, along RA = 173° ± 12°, Dec. = 10° ± 9°, the direction being within |$\stackrel{\lt }{_{\sim }}2\sigma$| of the CMBR dipole. Since a genuine solar motion would not depend upon the method or the data set employed, large discrepancies seen among various dipole amplitudes could imply that these dipoles, including the CMBR one, might not pertain to observer's peculiar motion. However, a common direction for various dipoles might indicate a preferred direction in the Universe, implying an intrinsic anisotropy, in violation of the cosmological principle, a cornerstone of the modern cosmology. [ABSTRACT FROM AUTHOR]

Odd Radio Circles or ORCs are recently discovered edge-brightened, low surface brightness circular radio sources. The progenitors and astrophysical processes responsible for their origins are presently debated. Some ORCs are host-less and some appear to be hosted in distant quiescent galaxies. Two plausible explanations consider ORCs as nearby supernova remnants with sizes a few hundred parsec in the intragroup medium of the Local Group of galaxies or alternatively shocked haloes of a few hundred kpc extent around distant galaxies. The input shock energy required to create ORCs of a few hundred kpc size is estimated in a range of 1055–1059 erg. It is shown here that the cumulative energy in unbound debris ejected from multiple (105–109) tidal disruption events over ∼100 Myr period around a central massive black hole can meet the required energies to generate ORCs around some galaxies, which have recently undergone a merger. The potential hosts for ORCs are identified here as abundant post-starburst galaxies at intermediate redshifts having massive black holes. A causal connection between ORC around quiescent galaxies and tidal disruption may find support in the observed dominance of tidal disruption events in post-starburst galaxies. [ABSTRACT FROM AUTHOR]

Our work aims to identify the miscellaneous radio galaxies (MRGs) using the LOFAR Two‐meter Sky Survey First Data Release (LoTSS DR1) at 144 MHz. The miscellaneous radio sources are very rare because of their peculiar morphological radio structure, which does not match with the known classes of radio sources. We find only four such MRGs by manually examining 18,500 samples. The peculiar morphology is not found in other radio frequencies 1400, 150, and 325 MHz. We estimate different physical parameters like spectral index, radio luminosity, and radio power of these sources. Among the four MRGs, J1428+4556 has the highest linear size of 3.972 Mpc and can be considered a giant radio galaxy. We also try to present the known galaxy cluster association with these MRGs. We find that the MRGs are associated with at least one galaxy cluster within 1 Mpc radius. The basic parameters such as mass, radius, and richness of the clusters are also noted. [ABSTRACT FROM AUTHOR]

We investigate the molecular gas properties, especially the dense molecular gas in NGC 1614, using the ALMA (Atacama Large Millimeter/ submillimeter Array) high resolution archival data of 12 CO(1-0), 13 CO(1-0), 12 CO(3-2), 12 CO(6-5), HCN(3-2), HCO + (3-2), HCN(4-3), and HCO + (4-3). From the high-resolution integrated intensity maps, a ring structure was detected in the central region (< 1 kpc), and the molecular gas mainly distributes in the central region while there is little gas in the nucleus. The 12 CO(1-0) shows an extended structure to the south, north, and southeast, and CO (J ⩾ 3 , J is the quantum number of rotational vibration levels), HCN, and HCO + show that the dense gas mainly concentrated in the central region. Similarly, HCN(4-3)/ 12 CO(1-0) and HCO + (4-3)/ 12 CO(1-0) ratio maps show that the dense molecular gas is mainly concentrated in the ring of the central region. The HCN/HCO + ratios show that the different regions of the starburst ring might have different excitation conditions. The variations of HCN/HCO + values in different region of central region may be due to the gas density and temperature. For HCN/HCO + (4-3) ratio map, the higher intensity values (∼ 0.44 ± 0.04) were obtained in the eastern and western region of the ring, compared to the northern and southern region (∼ 0.35 ± 0.03). For HCN/HCO + (3-2) ratio map, the higher values (∼ 0.38 ± 0.04) are distributed at peak location of HCN(3-2) emission, while the lower values (∼ 0.3 ± 0.03) are distributed at the northwestern and southeastern region of the ring. The mechanism of variations of HCN/HCO + values in the central region of the galaxy has been discussed in the article. [ABSTRACT FROM AUTHOR]

Despite their relative sparseness, during the recent years it has become more and more clear that extragalactic radio sources (both AGN and star-forming galaxies) constitute an extremely interesting mix of populations, not only because of their intrinsic value, but also for their fundamental role in shaping our universe the way we see it today. Indeed, radio-active AGN are now thought to be the main players involved in the evolution of massive galaxies and clusters. At the same time, thanks to the possibility of being observed up to very high redshifts, radio galaxies can also provide crucial information on both the star-formation history of our universe and on its large-scale structure properties and their evolution. In the light of present and forthcoming facilities such as LOFAR, MeerKAT and SKA that will probe the radio sky to unprecedented depths and widths, this review aims at providing the current state of the art on our knowledge of extragalactic radio sources in connection with their hosts, large-scale environments and cosmological context. [ABSTRACT FROM AUTHOR]

The environment of S187, a nearby H  ii region (1.4 ± 0.3 kpc), is analyzed. A surrounding shell has been studied in the H  i line, molecular lines, and also in infrared and radio continua. We report the first evidence of a clumpy H  i environment in its photodissociation region. A background radio galaxy enables the estimation of the properties of cold atomic gas. The estimated atomic mass fraction of the shell is ∼260 M⊙, the median spin temperature is ∼50 K, the shell size is ∼4 pc with typical wall width around 0.2 pc. The atomic shell consists of ∼100 fragments. The fragment sizes correlate with mass with a power-law index of 2.39–2.50. The S187 shell has a complex kinematical structure, including the expanding quasi-spherical layer, molecular envelope, an atomic sub-bubble inside the shell and two dense cores (S187 SE and S187 NE) at different stages of evolution. The atomic sub-bubble inside the shell is young, contains a Class II young stellar object and OH maser in the centre and the associated YSOs in the walls of the bubble. S187 SE and S187 NE have similar masses (∼1200 and ∼900 M⊙, respectively). S187 SE is embedded into the atomic shell and has a number of associated objects, including high-mass protostars, outflows, maser sources, and other indicators of ongoing star formation. No YSOs inside S187 NE were detected, but indications of compression and heating by the H  ii region exist. [ABSTRACT FROM AUTHOR]

Giant radio galaxies (GRGs) are radio galaxies that have projected linear extents of more than 700 kpc or 1 Mpc, depending on definition. We have carried out a careful visual inspection in search of GRGs of the Boötes LOw-Frequency ARray Deep Field image at 150 MHz. We identified 74 GRGs with a projected size larger than 0.7 Mpc of which 38 are larger than 1 Mpc. The resulting GRG sky density is about 2.8 (1.43) GRGs per square degree for GRGs with linear size larger than 0.7 (1) Mpc. We studied their radio properties and the accretion state of the host galaxies using deep optical and infrared survey data and determined flux densities for these GRGs from available survey images at both 54 MHz and 1.4 GHz to obtain integrated radio spectral indices. We show the location of the GRGs in the P–D diagram. The accretion mode on to the central black holes of the GRG hosts is radiatively inefficient suggesting that the central engines are not undergoing massive accretion at the time of the emission. Interestingly, 14 out of 35 GRGs for which optical spectra are available show a moderate star-formation rate (10–100 |$\rm M_{\odot }\,yr^{-1}$|⁠). Based on the number density of optical galaxies taken from the Dark Energy Spectroscopic Instrument survey DR9 photometric redshift catalogue, we found no significant differences between the environments of GRGs and other radio galaxies, at least for redshift up to z = 0.7. [ABSTRACT FROM AUTHOR]