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Active galactic nuclei (AGNs) play an integral role in galaxy formation and evolution by influencing galaxies and their environments through radio jet feedback. Historically, interpreting observations of radio galaxies and quantifying radio jet feedback has been challenging due to degeneracies between their physical parameters. In particular, it is well established that different combinations of jet kinetic power and environment density can yield indistinguishable radio continuum properties, including apparent size and Stokes I luminosity. We present an approach to breaking this degeneracy by probing the line-of-sight environment with Faraday rotation. We study this effect in simulations of three-dimensional relativistic magnetohydrodynamic AGN jets in idealized environments with turbulent magnetic fields. We generate synthetic Stokes I emission and Faraday rotation measure (RM) maps, which enable us to distinguish between our simulated sources. We find enhanced RMs near the jet head and lobe edges. We show that increasing the environment density and the average cluster magnetic field strength broadens the distribution of Faraday rotation measure values. We study the depolarization properties of our sources, finding that the hotspot regions depolarize at lower frequencies than the lobes. We quantify the effect of depolarization on the RM distribution, finding that the frequency at which the source is too depolarized to measure the RM distribution accurately is a probe of environmental properties. This technique offers a range of new opportunities for upcoming surveys, including probing radio galaxy environments and determining more accurate estimates of the AGN feedback budget. [ABSTRACT FROM AUTHOR]

We report the discovery of a unique object in the MeerKAT Galaxy Cluster Legacy Survey (MGCLS) using the machine learning anomaly detection framework astronomaly. This strange, ring-like source is 30′ from the MGCLS field centred on Abell 209, and is not readily explained by simple physical models. With an assumed host galaxy at redshift 0.55, the luminosity (1025 W Hz−1) is comparable to powerful radio galaxies. The source consists of a ring of emission 175 kpc across, quadrilateral enhanced brightness regions bearing resemblance to radio jets, two 'ears' separated by 368 kpc, and a diffuse envelope. All of the structures appear spectrally steep, ranging from −1.0 to −1.5. The ring has high polarization (25 per cent) except on the bright patches (<10 per cent). We compare this source to the Odd Radio Circles recently discovered in ASKAP data and discuss several possible physical models, including a termination shock from starburst activity, an end-on radio galaxy, and a supermassive black hole merger event. No simple model can easily explain the observed structure of the source. This work, as well as other recent discoveries, demonstrates the power of unsupervised machine learning in mining large data sets for scientifically interesting sources. [ABSTRACT FROM AUTHOR]

In this work we explore the potential of multidomain multibranch convolutional neural networks (CNNs) for identifying comparatively rare giant radio galaxies from large volumes of survey data, such as those expected for new generation radio telescopes like the SKA and its precursors. The approach presented here allows models to learn jointly from multiple survey inputs, in this case NVSS and FIRST, as well as incorporating numerical redshift information. We find that the inclusion of multiresolution survey data results in correction of 39 per cent of the misclassifications seen from equivalent single domain networks for the classification problem considered in this work. We also show that the inclusion of redshift information can moderately improve the classification of giant radio galaxies. [ABSTRACT FROM AUTHOR]

In this paper, we present the identification of five previously unknown giant radio galaxies (GRGs) using Data Release 1 of the Radio Galaxy Zoo citizen science project and a selection method appropriate to the training and validation of deep learning algorithms for new radio surveys. We associate one of these new GRGs with the brightest cluster galaxy (BCG) in the galaxy cluster GMBCG J251.67741+36.45295 and use literature data to identify a further 13 previously known GRGs as BCG candidates, increasing the number of known BCG GRGs by |$\gt 60$|  per cent. By examining local galaxy number densities for the number of all known BCG GRGs, we suggest that the existence of this growing number implies that GRGs are able to reside in the centres of rich (∼1014 M⊙) galaxy clusters and challenges the hypothesis that GRGs grow to such sizes only in locally underdense environments. [ABSTRACT FROM AUTHOR]

We investigate the role of environment on radio galaxy properties by constructing a sample of large (≳100 kpc), nearby (⁠|$z$| < 0.3) radio sources identified as part of the Radio Galaxy Zoo citizen science project. Our sample consists of 16 Fanaroff-Riley Type II (FR-II) sources, 6 FR-I sources, and 1 source with a hybrid morphology. FR-I sources appear to be hosted by more massive galaxies, consistent with previous studies. In the FR-II sample, we compare the degree of asymmetry in radio lobe properties to asymmetry in the radio source environment, quantified through optical galaxy clustering. We find that the length of radio lobes in FR-II sources is anticorrelated with both galaxy clustering and lobe luminosity. These results are in quantitative agreement with predictions from radio source dynamical models and suggest that galaxy clustering provides a useful proxy for the ambient gas density distribution encountered by the radio lobes. [ABSTRACT FROM AUTHOR]

We study the mutual alignment of radio sources within two surveys, Faint Images of the Radio Sky at Twenty-centimetres (FIRST) and TIFR GMRT Sky Survey (TGSS). This is done by producing two position angle catalogues containing the preferential directions of respectively 30 059 and 11 674 extended sources distributed over more than 7000 and 17 000 deg2. The identification of the sources in the FIRST sample was performed in advance by volunteers of the RadioGalaxy Zoo (RGZ) project,while for the TGSS sample it is the result of an automated process presented here. After taking into account systematic effects, marginal evidence of a local alignment on scales smaller than 2.5 deg is found in the FIRST sample. The probability of this happening by chance is found to be less than 2 per cent. Further study suggests that on scales up to 1.5 deg the alignment is maximal. For one third of the sources, the RGZ volunteers identified an optical counterpart. Assuming a flat ⋀ cold dark matter cosmology with Ωm = 0.31,Ω⋀ = 0.69, we convert the maximum angular scale on which alignment is seen into a physical scale in the range [19, 38] Mpc h -1 70 . This result supports recent evidence reported by Taylor and Jagannathan of radio jet alignment in the 1.4 deg2 ELAIS N1 field observed with the Giant Metrewave Radio Telescope. The TGSS sample is found to be too sparsely populated to manifest a similar signal. [ABSTRACT FROM AUTHOR]

The kinetic power of radio jets is a quantity of fundamental importance to studies of the AGN feedback process and radio galaxy physics. A widely used proxy for jet power is the extended radio luminosity. A number of empirical methods have been used to calibrate a scaling relationship between jet power (Q) and radio luminosity (L) of the formlog(Q) = βL log (L) + C. The regression slope has typically been found to be βLL ~ 0.7-0.8. Here we show that the previously reported scaling relations are strongly affected by the confounding variable, distance. We find that in a sample of FRI X-ray cavity systems, after accounting for the mutual distance dependence, the jet power and radio luminosity are only weakly correlated, with slope βL &#8776 0.3: significantly flatter than previously reported. We also find that in previously used samples of high-power sources, no evidence for an intrinsic correlation is present when the effect of distance is accounted for. Using a simple model we show that βL is expected to be significantly lower in samples of FRI radio galaxies than it is for FRIIs, due to the differing dynamics for these two classes of radio source. For FRI X-ray cavity systems the model predicts βL(FRI) ≳ 0.5 in contrast to FRII radio galaxies, for which βL(FRII) ≳ 0.8. We discuss the implications of our finding for studies of radio mode feedback, and radio galaxy physics. [ABSTRACT FROM AUTHOR]

We present results from the first 12 months of operation of Radio Galaxy Zoo, which upon completion will enable visual inspection of over 170 000 radio sources to determine the host galaxy of the radio emission and the radio morphology. Radio Galaxy Zoo uses 1.4 GHz radio images from both the Faint Images of the Radio Sky at Twenty Centimeters (FIRST) and the Australia Telescope Large Area Survey (ATLAS) in combination with mid-infrared images at 3.4 µm from the Wide-field Infrared Survey Explorer (WISE) and at 3.6 µm from the Spitzer Space Telescope. We present the early analysis of the WISE mid-infrared colours of the host galaxies. For images in which there is >75 per cent consensus among the Radio Galaxy Zoo cross-identifications, the project participants are as effective as the science experts at identifying the host galaxies. The majority of the identified host galaxies reside in the midinfrared colour space dominated by elliptical galaxies, quasi-stellar objects and luminous infrared radio galaxies. We also find a distinct population of Radio Galaxy Zoo host galaxies residing in a redder mid-infrared colour space consisting of star-forming galaxies and/or dustenhanced non-star-forming galaxies consistent with a scenario of merger-driven active galactic nuclei (AGN) formation. The completion of the full Radio Galaxy Zoo project will measure the relative populations of these hosts as a function of radio morphology and power while providing an avenue for the identification of rare and extreme radio structures. Currently, we are investigating candidates for radio galaxies with extreme morphologies, such as giant radio galaxies, late-type host galaxies with extended radio emission and hybrid morphology radio sources. [ABSTRACT FROM AUTHOR]