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The unified model of jetted active galactic nuclei (AGNs) based on intrinsic properties presumes that the blazar subtypes of BL Lacertae objects (BLs) and flat-spectrum radio quasars (FSRQs) are aligned equivalents of Fanaroff–Riley type I (FR I) and Fanaroff–Riley type II (FR II) radio galaxies (RGs) from where their parent sources are obtained. Using compiled radio, X-ray and γ -ray data of 397 Fermi Large Area Telescope (Fermi-LAT) blazars and 153 non-Fermi detected RGs, we computed the γ -ray core-dominance parameter (Rγ) and γ -ray emission components (beamed and unbeamed) to study the consequences of relativistic beaming and orientation effects on γ -ray properties of radio RGs, BLs and FSRQs. Data analysis shows that the distributions of RX and Rγ, on average, are consistent with the prediction of the unified scheme in which FSRQs and BLs are strongly beamed and inclined at smaller angles than RGs. Through statistical tests with chance probability, p < 0.05 , we find that the distributions of RX and Rγ for radio galaxies and the blazar subtypes are not significantly different. There is a regular positive trend (r > + 0.60 ) in the variation of radio core-dominance parameter – X-ray luminosity (R − L x ) data from radio galaxies to FSRQs through BLs, which suggests that radio galaxies could be relativistically less beamed population of jetted AGNs. The results are consistent with the unified model for radio galaxies and the conventional blazar subtypes. [ABSTRACT FROM AUTHOR]

The issue of radiation mechanisms triggered in 1950–60s the first applications of plasma physics to understand the nature of radio galaxies. This interplay has steadily intensified during the past five decades due to the premise of in-situ acceleration of relativistic electrons occurring in the lobes of radio galaxies. This article briefly traces the chain of these remarkable developments, largely from an observational perspective. We recount several observational and theoretical milestones established along the way and the lessons drawn from them. We also present a new observational clue about in-situ acceleration of the relativistic particles radiating in the lobes of radio galaxies, gleaned by us from the very recently published sensitive radio observations of a tailed radio source in the galaxy cluster Abell 1033. [ABSTRACT FROM AUTHOR]

We present an optical-to-radio study of the BL Lac object S4 0954+658 observations during 1998–2023. The measurements were obtained with the SAO RAS Zeiss-1000 and AS-500/2 0.5-m telescopes in 2003–2023, with the RATAN-600 radio telescope at 1.25 (0.96, 1.1), 2.3, 4.7 (3.7, 3.9), 8.2 (7.7), 11.2, 22.3 (21.7) GHz in 1998–2023, with the IAA RAS RT-32 Zelenchukskaya and Badary telescopes at 5.05 and 8.63 GHz in 2020–2023, and with the RT-22 single-dish telescope of CrAO RAS at 36.8 GHz in 2009–2023. In this period the blazar was showing extremely high broadband activity with the variability amplitude of the flux densities up to 70–100 both in the optical and radio domains. During the period of 2014–2023 the blazar displayed extremely high activity in the radio wavelengths, and we detected multiple radio flares of varying amplitude and duration. The large flares last on average from 0.3 to 1 year at 22–36.8 GHz and slightly longer at 5–11.2 GHz. The optical flares are shorter and last 7–50 days. The characteristic time scale of variation at 5–22 GHz is about 100 days in the most active epoch of 2014–2023 and about 1000 days for the state with lower activity in 2009–2014. We found a general correlation between the optical, radio, and -ray flux variations, which suggesting that we observe the same photon population from different emission regions. We estimated the linear size of this region as 0.5–2 pc for different conditions. A broadband radio spectrum with two components of the S4 0954+658 jet was modeled using both electrons and protons as emitting particles. The results suggest that the synchrotron radio waves in this AGN may be produced by relativistic protons. [ABSTRACT FROM AUTHOR]

Study of high-redshift radio galaxies (HzRGs) can shed light on the active galactic nuclei (AGNs) evolution in massive elliptical galaxies. The vast majority of observed high-redshift AGNs are quasars, and there are very few radio galaxies at redshifts . We present the radio properties of 173 sources optically identified with radio galaxies at with flux densities mJy. Literature data were collected for compilation of broadband radio spectra, estimation of radio variability, radio luminosity, and radio loudness. Almost 60 of the galaxies have steep or ultra-steep radio spectra; 22 have flat, inverted, upturn, and complex spectral shapes, and 18 have peaked spectra (PS). The majority of the PS sources in the sample (20/31) are megahertz-peaked spectrum source candidates, i.e. possibly very young and compact radio galaxies. The median values of the variability indices at 11 and 5 GHz are and , which generally indicates a weak or moderate character of the long-term variability of the studied galaxies. The typical radio luminosity and radio loudness are erg s and respectively. We have found less prominent features of the bright compact radio cores in our sample compared to high-redshift quasars at . The variety of the obtained radio properties shows the different conditions for the formation of radio emission sources in galaxies. [ABSTRACT FROM AUTHOR]

We present a catalog of sources detected by the Mikhail Pavlinsky ART-XC telescope onboard the SRG space observatory during the observations of the Galactic plane region near a longitude (L20 field) in October 2019. The L20 field was observed four times in the scanning mode, which provided a uniform coverage of the sky region with a total area of with a median sensitivity of erg s cm (at 50 detection completeness) in the 4–12 keV energy band. As a result, we have detected 29 X-ray sources at a statistically significant level, 11 of which have not been detected previously by other X-ray observatories. Preliminary estimates show that four of them can presumably be extragalactic in nature. We also show that the source SRGA J183220.1 103508 (CXOGSG J183220.8 103510) is most likely a galaxy cluster containing a bright radio galaxy at redshift . [ABSTRACT FROM AUTHOR]

Understanding the spectral properties of sources is crucial for the characterization of the radio source population. In this work, we have extensively studied the ELAIS N1 field using various low-frequency radio observations. For the first time, we presented the 1250 MHz observations of the field using the upgraded Giant Meterwave Radio Telescope (uGMRT) that reach a central off-source RMS noise of ∼ 12 μ Jy beam - 1 . A source catalog of 1086 sources is compiled at 5 σ threshold (>60 μ Jy) to derive the normalized differential source counts at this frequency, which is consistent with existing observations and simulations. We presented the spectral indices derived in two ways: two-point spectral indices and by fitting a power-law. The latter yielded a median α = - 0.57 ± 0.14 , and we identified nine ultra-steep spectrum sources using these spectral indices. Further, using a radio color diagram, we identified the three mega-hertz peaked spectrum (MPS) sources, while three other MPS sources are identified from the visual inspection of the spectra, the properties of which are discussed. In our study of the classified sources in the ELAIS N1 field, we presented the relationship between α and z. We found no evidence of an inverse correlation between these two quantities and suggested that the nature of the radio spectrum remains independent of the large-scale properties of the galaxies that vary with redshifts. [ABSTRACT FROM AUTHOR]

We study the close proximity of the well-known and well-studied 3C31 class FRI radio galaxy in order to reveal the influence of the environment on an extragalactic radio source. It was shown that about 110 million years ago the galaxies NGC 380 and NGC 386 were located near the galaxy NGC 383 (the parent galaxy of 3C31). On the other hand, the modeling of the spectral characteristics of the radio emission of the central part of the radio galaxy 3C31 gives an estimate of the age of the central jet of about 100 million years. Therefore, it can be assumed that one of the possible reasons for the appearance or resumption of the radioactivity of the galaxy NGC 383 may be a triple close passage of galaxies. [ABSTRACT FROM AUTHOR]

Radio-loud compact radio sources (CRSs) are characterised by morphological compactness of the jet structure centred on the active nucleus of the galaxy. Most of the local elliptical galaxies are found to host a CRS with nuclear luminosities lower than those of typical quasars, ≲ 10 42 erg s - 1 . Recently, low-luminosity CRSs with a LINER-like optical spectrum have been named Fanaroff–Riley (FR) type 0 to highlight their lack of substantially extended radio emission at kpc scales, in contrast with the other Fanaroff–Riley classes, full-fledged FR Is and FR II radio galaxies. FR 0s are the most abundant class of radio galaxies in the local Universe, and characterised by a higher core dominance, poorer Mpc-scale environment and smaller (sub-kpc scale, if resolved) jets than FR Is. However, FR 0s share similar host and nuclear properties with FR Is. A different accretion–ejection paradigm from that in place in FR Is is invoked to account for the parsec-scale FR 0 jets. This review revises the state-of-the-art knowledge about FR 0s, their nature, and which open issues the next generation of radio telescopes can solve in this context. [ABSTRACT FROM AUTHOR]

The discovery of γ - ray emitting Seyfert galaxies has opened a new unified scheme of active galactic nuclei (AGN) in which jetted Seyfert galaxies are viewed as young counterparts of radio loud AGN. In this paper, we investigate the relationship between gamma-ray (γ - ray) properties of jetted Seyfert galaxies and those of traditionally radio galaxies, radio quasars and BL Lac objects. Results show that jetted Seyfert galaxies appear as low luminosity tail of the radio loud AGNs on the luminosity redshift (Lγ – z) plane, indicating an evolutionary link between them. Nevertheless, narrow-line Seyfert galaxies (NLS1s) do not share similar characteristics with Seyfert galaxies as they possess higher luminosities and redshift than Seyfert galaxies, suggestive that NLS1s are more evolved sources. Analyses of γ – ray and radio core-dominance show that for each subclass of jetted AGN, the beaming angle is wider for radio than for γ - ray emissions. While Seyferts and radio galaxies, on average, have similar low inclination to the line of sight, NLS1 objects have orientations similar to quasars and BL Lacs. There is a significant correlation (r ~ 0.7) between the γ - ray core dominance and γ - ray luminosity. The results are consistent with the revised unification scheme and suggests that NLS1s are highly beamed sources whose parent populations can be found among the regular Seyferts and/or radio galaxies [ABSTRACT FROM AUTHOR]

This paper is an extension of the study by Khamitov et al. (2022) with regard to the catalog and the astrophysical interpretation of the imitation of significant proper motions in active galactic nuclei (AGNs) and quasars based on data from the Gaia space observatory. We present a sample of SRG/eROSITA X-ray sources in the eastern Galactic hemisphere () having significant proper motions in the Gaia EDR3 measurements with the confirmed extragalactic nature of the objects. The catalog consists of 248 extragalactic sources with spectroscopically measured redshifts. The catalog includes all of the objects available in the SIMBAD database and coincident with the identified optical counterpart within 0.5 arcsec. Eighteen sources with spectroscopically measured redshifts from observations with the Russian–Turkish 1.5-m telescope RTT-150 (Khamitov et al. 2022) have been additionally included in the catalog. The sources in the catalog are AGNs of various types (Sy1, Sy2, LINER), quasars, radio galaxies, and star-forming galaxies. The imitation of significant proper motions can be explained (by the VIM effect previously known in astrometry) by the presence of transient events on the line of sight in the vicinity of AGNs and quasars (within the Gaia optical resolution element). Among such astrophysical events are supernova outbursts, tidal disruption events in binary AGNs, the variability of high-mass supergiants, the presence of OB associations against the background of AGNs with a variable brightness, etc. The model of outbursts with a fast rise–exponential decay profile allows the variable positional parameters of most sources observed in Gaia to be described. This approach can be used as an independent way of detecting transient events in the vicinity of AGNs (on scales of several hundred parsecs in the plane of the sky) based on data from the SRG/eROSITA catalogs of X-ray sources and the optical Gaia catalog. [ABSTRACT FROM AUTHOR]

A small subset of extragalactic double radio sources, termed HYbrid MOrpholgy Radio Sources (HYMORS), is distinguished by a very unusual, hybrid morphology in terms of Fanaroff–Riley (FR) classification. In HYMORS, one radio lobe appears edge-darkened (FR I), while the other shows a well-defined emission peak near its outer edge (edge-brightened, FR II). Such sources are rare, but critical for constraining the mechanism responsible for FR dichotomy, a widely debated issue in extragalactic astrophysics. Here, we highlight the need for caution in assigning FR type, in view of some upcoming observational campaigns to confirm HYMORS among the candidates. To illustrate this, we highlight the cases of three radio sources, which have been perceived to be HYMORS, including the radio galaxy 0500 + 630 (4C + 63.07), which has been claimed to be a good, original example of a HYMORS, with a FR I western lobe and a FR II eastern lobe marked by a prominent terminal hot spot. However, its recent VLASS map at 3 GHz has revealed that the western lobe actually extends much farther out than reported and terminates in a well-defined emission peak. This implies that the source is a regular FR II radio galaxy and not a HYMORS. We also provide a brief perspective of the HYMORS phenomenon and underscore the need to confirm a FR I classification by ruling out additional FR II characteristics, such as an inward lobe-widening and spectral steepening, as well as a lack of prominent radio jet within the lobe. [ABSTRACT FROM AUTHOR]

Drawing on astronomical discoveries made in the past 25 years, the paper discusses possible causes of the phenomenon perceived as the "accelerated expansion of the universe." In 1998, to confirm the "accelerated expansion of the universe," the High-Z SN Search Team tested and rejected the hypothesis about the effect produced by a local void — Hubble bubble — using data on 44 Type Ia supernovae (SNe Ia), which was believed to be an alternative to the positive cosmological constant. Also in 1998, the present author and specialists of the Computing Center of the Academy of Sciences (CC RAS) discovered divergent dipole anisotropy in the redshift of 383 quasars and radio galaxies along the Virgo – Leo ↔ Eridanus – Aquarius axis when testing the MCM-stat M program for multivariate statistical analysis using standard reference data. In 2007, the issues associated with anisotropy caught the attention of cosmologists, while in 2016, the High-Z SN Search Team and the Carnegie–Chicago Hubble program initiated a discussion about the impasse in cosmology. An additional analysis revealed that the dipole anisotropy in the redshift of SNe Ia, as well as radio galaxies, is inversely oriented with respect to the dipole anisotropy of quasars. [ABSTRACT FROM AUTHOR]

Diffuse radio emission has been detected in a considerable number of galaxy clusters and groups, revealing the presence of pervasive cosmic magnetic fields, and of relativistic particles in the large scale structure of the Universe. Since the radio emission in galaxy systems is faint and its spectrum is steep, its observations are largely limited by the instrument sensitivity and frequency of observation, leading to a dearth of information, more so for lower-mass systems. The recent commissioning or upgrade of several large radio telescope arrays, particularly at the low frequency bands (

The cosmological principle states that the Universe is statistically homogeneous and isotropic at large distance scales. Currently, there exist many observations which indicate a departure from this principle. It has been shown that many of these observations can be explained by invoking superhorizon cosmological perturbations and may be consistent with the Big Bang paradigm. Remarkably, these modes simultaneously explain the observed Hubble tension, i.e., the discrepancy between the direct and indirect measurements of the Hubble parameter. We propose several tests of the cosmological principle using SKA. In particular, we can reliably extract the signal of dipole anisotropy in the distribution of radio galaxies. The superhorizon perturbations also predict a significant redshift dependence of the dipole signal, which can be well tested by the study of signals of reionization and the dark ages using SKA. We also propose to study the alignment of radio galaxy axes as well as their integrated polarization vectors over distance scales ranging from a few Mpc to Gpc. We discuss data analysis techniques that can reliably extract these signals from data. [ABSTRACT FROM AUTHOR]

The unique morphology of head–tail (HT) radio galaxies suggests that radio jets and their intra-cluster medium interact strongly. We conducted a systematic search for HT radio galaxies using the LOFAR two-meter sky survey first data release (LoTSS DR1) at 144 MHz. In this paper, a catalog of 55 new HT radio galaxies is presented, 10 of which are narrow-angle tailed sources (NATs) and 45 are wide-angle-tailed sources (WATs). NATs are characterized by tails that are bent like a narrow 'V' shape with a <90 ∘ opening angle. The opening angle between jets in WAT radio galaxies is >90 ∘ , exhibiting wide 'C'-like morphologies. We found that 30 out of 55 HT radio galaxies reported in this paper are associated with known galaxy clusters. Most of the sources presented in the current paper have redshifts <0.5. Various physical properties and statistical studies of these HT radio galaxies are presented. [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]

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]

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]

Abstract—We study the radio variability of galaxies with and without sources of hydroxyl (OH) megamaser radiation based on the continuum radio measurements conducted in 2019–2022 with the radio telescope RATAN-600 at frequencies of 2.3, 4.7, 8.2, and 11.2 GHz. Presumably, radio continuum emission significantly affects the megamaser radiation brightness, therefore, such a characteristic as the variability of radio emission is important for determining the OHM galaxies parameters. With additional data from the literature, the parameters of radio variability on a time scale up to 30 years were estimated. The median values of the variability index for 48 OHM galaxies are in the range – , and for 30 galaxies without OH emission they are – . For some individual galaxies in both samples flux density variations reach 30–50%. These sources either are commonly associated with AGNs or reveal active star formation. Generally, the radio variability of luminous infrared galaxies with and without OH megamaser emission is moderate and of the same order of magnitude on long time scales. From estimating the spectral energy distribution parameters in a broad frequency range (from MHz to THz), we determined the spectral index below 50 GHz and the color temperatures of dust components for megamaser and control sample galaxies. At a level of , there are no statistically significant differences in the distribution of these parameters for the two samples, as well there are no statistically significant correlations between the dust color temperatures and the variability index or luminosity in the OH line. [ABSTRACT FROM AUTHOR]

We present radio continuum observations of NGC 2082 using ASKAP, ATCA and Parkes telescopes from 888 MHz to 9000 MHz. Some 20 arcsec from the centre of this nearby spiral galaxy, we discovered a bright and compact radio source, J054149.24–641813.7, of unknown origin. To constrain the nature of J054149.24–641813.7, we searched for transient events with the Ultra-Wideband Low Parkes receiver, and compare its luminosity and spectral index to various nearby supernova remnants (SNRs), and fast radio burst (FRB) local environments. Its radio spectral index is flat (α = 0.02 ± 0.09 ), which is unlikely to be either an SNR or pulsar. No transient events were detected with the Parkes telescope over three days of observations, and our calculations show J054149.24–641813.7 is two orders of magnitude less luminous than the persistent radio sources associated with FRB 121102 and 190520B. We find that the probability of finding such a source behind NGC 2082 is P = 1.2 % , and conclude that the most likely origin for J054149.24–641813.7 is a background quasar or radio galaxy. [ABSTRACT FROM AUTHOR]

Estimates of the physical parameters of the hot spot A of the radio galaxy Cygnus A were obtained from radio astronomical observations. To estimate the physical parameters of this radio source, we took the dimensions of a spherically symmetric inhomogeneous model of the spot A (without voids inside), the spectrum of which coincides with the radio spectrum of the hot spot A. The most probable average value of the magnetic field induction (averaged over the volume of the radio source) is B = 2.7 × 10–3 G. The average energy density of relativistic electrons is Ее = 1.8 × 10–6 erg/cm3. The average energy of relativistic electrons exceeds the energy of the magnetic field by eight times. The obtained parameters of hot spot A are compared with the estimates of these parameters obtained from X-ray observations. If we take the dimensions of this radio source model (θ ≈ 0.6 ) as the size of the X-ray source, then we obtain the same field B = 2.6 × 10–3 G from X-ray observations. [ABSTRACT FROM AUTHOR]

A model of the population of ultraluminous X-ray sources (ULXs) in binary systems with black hole (BH) accretors is constructed by hybrid population synthesis and is compared with the model of the population of ULXs with magnetized neutron stars (NSs) that can be observed as pulsating ULXs (Kuranov et al. 2020). A model of the formation of BHs whereby their mass is determined by the mass of the CO core immediately before its collapse () and "delayed" and "rapid" collapse models (Fryer et al. 2012) are considered. The possible transiency of ULXs due to accretion disk instability is taken into account. The parameters and evolution of ULXs in galaxies with a constant star formation rate (SFR) and in those with an old stellar population after an instantaneous star formation burst are computed. The maximum number of ULXs with BHs () is reached in galaxies with a stationary yr Gyr after the beginning of star formation. ULXs observed after the end of star formation are close binary systems in which BHs and/or NSs formed before the end of star formation, while long-lived donors with a mass continue to overflow their Roche lobes after its end or have filled their Roche lobes even later. Several Gyr after the end of star formation the number of ULXs in galaxies with a mass is no more than 0.1, most of them are ULXs with NSs. Persistent sources with a Roche-lobe-overflowing optical star dominate in ULXs with NSs, irrespective of the adopted star formation model. The transient sources are an order of magnitude fewer. The ULXs accreting from the stellar wind of the optical component are an order of magnitude fewer than the sources with accretion via Roche lobe overflow. [ABSTRACT FROM AUTHOR]

We present imaging and photometric studies of the radio galaxy NGC 1316 (Fornax A) using high spatial resolution near-ultraviolet (NUV) and far-ultraviolet (FUV) imaging telescopes of the first Indian multi-wavelength space observatory AstroSat. The residual maps of UV emission obtained from the subtraction of smooth models witness peculiar features within the central few kpc (1–2 kpc) region. The spatial correspondence between the radio emission maps and FUV imaging study reveal that the UV emitting sources are displaced away from the centre by the AGN outburst (radio jet). The presence of rims and clumpy structures in the outskirt of this galaxy delineate that the galaxy has acquired a large fraction of gas through merger-like events and is still in the process of settling. The estimates of the star formation rates (SFR) using FUV and NUV luminosities are found to be 0.15 M ⊙ yr - 1 and 0.36 M ⊙ yr - 1 , respectively, and provide the lower limit due to the screen effect. The estimated lower rates of SFR in this galaxy probably represent its quenching due to the AGN driven outflows emanating from the central engine of NGC 1316. [ABSTRACT FROM AUTHOR]

In this paper, we carry out an assessment of cosmic distance duality relation (CDDR) based on the latest observations of HII galaxies acting as standard candles and ultra-compact structure in radio quasars acting as standard rulers. Particularly, two machine learning reconstruction methods [Gaussian Process (GP) and Artificial Neural Network (ANN)] are applied to reconstruct the Hubble diagrams from observational data. We show that both approaches are capable of reconstructing the current constraints on possible deviations from the CDDR in the redshift range z ∼ 2.3 . Considering four different parametric methods of CDDR, which quantify deviations from the CDDR and the standard cosmological model, we compare the results of the two different machine learning approaches. It is observed that the validity of CDDR is in well agreement with the current observational data within 1 σ based on the reconstructed distances through GP in the overlapping redshift domain. Moreover, we find that ultra-compact radio quasars could provide 10 - 3 -level constraints on the violation parameter at high redshifts, when combined with the observations of HII galaxies. In the framework of ANN, one could derive robust constraints on the violation parameter at a precision of 10 - 2 , with the validity of such distance duality relation within 2 σ confidence level. [ABSTRACT FROM AUTHOR]

Recent studies have shown that among the population of radio-loud active galactic nuclei in the local U-niverse, they numerically dominate compact radio sources of the FR0 class. In this paper, we present ob-servation results of a sample of 33 FR0 radio galaxies with RATAN-600 in the first half of 2020. For the first time, quasi-simultaneous spectra of this class objects have been measured in the frequency range as wide as 2.25–22.3 GHz. Radio luminosity of the sampled objects at the frequency 4.7 GHz varies within erg/s, with the average value of erg/s. The data confirm the deficit of extended radio emission: the average value of the core-dominance parameter () substantially exceeds the values typical for FRI galaxies. Quasi-simultaneous spectra are flat, while in the range 4.7–8.2 GHz, the average spectral index is close to zero. The spectra of 44 percent of objects which have more than three quasi-simultaneous points have peaked-shaped profiles. Using additional data of catalogs allowed us to identify three new candidates for the sources with the maximum of the spectrum in the GHz range. A statistically significant correlation was found between the parsec scale jet power and the bolometric luminosity of the accretion disk: . In general, the spectra of the studied objects are flat and have a complex structure, which indicates a high opacity in the radio range and the contribution of several components to the total spectrum. [ABSTRACT FROM AUTHOR]

In this paper, we use the distributions of two-component radio emissions to investigate the consequences of relativistic beaming on the unified scheme of blazar populations and radio galaxies. Our results show remarkable continuity in the distributions of source luminosities (radio core and extended luminosities, L C and L E respectively as well as γ -ray luminosity L γ ) from radio galaxies at low luminosities to FSRQs at high luminosities through BL subclasses as expected in the blazar unification scheme in a sense suggesting that the sequence of BL Lacs, FSRQs and radio galaxies represents progressively misaligned populations of AGNs. Distribution of radio core-dominance is consistent with average projection angles of 13.5∘, 14.8∘, 16.8∘, 20.4∘ and 28.2∘ for ISPs, LSPs, FSRQs, HSPs, and radio galaxies, respectively. Linear regression analyses of our data yield significant anti-correlation (r > 0.60 ) between core-dominance parameter (C ) and L E in each individual subsample: the correlation is significant only when individual subsamples are considered. There is a systematic sequence of the distribution of the different subclasses on the C − L E plane. Nevertheless, little or no correlation between C and L C or between C and L γ (r < 0.50 ) was observed. There is a clear dichotomy between high synchrotron-peaking BL Lacs and other BL Lac subclasses. The results are consistent with a unified view for blazars and can be understood in terms of relativistic beaming persisting at largest scales. [ABSTRACT FROM AUTHOR]

Compact steep-spectrum (CSS) and peaked-spectrum (PS) radio sources are compact, powerful radio sources. The multi-frequency observational properties and current theories are reviewed with emphasis on developments since the earlier review of O'Dea (PASP 110:493–532, https://doi.org/10.1086/316162, 1998). There are three main hypotheses for the nature of PS and CSS sources. (1) The PS sources might be very young radio galaxies which will evolve into CSS sources on their way to becoming large radio galaxies. (2) The PS and CSS sources might be compact, because they are confined (and enhanced in radio power) by interaction with dense gas in their environments. (3) Alternately, the PS sources might be transient or intermittent sources. Each of these hypotheses may apply to individual objects. The relative number in each population will have significant implications for the radio galaxy paradigm. Proper motion studies over long time baselines have helped determine hotspot speeds for over three dozen sources and establish that these are young objects. Multi-frequency polarization observations have demonstrated that many CSS/PS sources are embedded in a dense interstellar medium and vigorously interacting with it. The detection of emission line gas aligned with the radio source, and blue-shifted Hi absorption, and [OIII] emission lines indicates that AGN feedback is present in these objects—possibly driven by the radio source. Also, CSS/PS sources with evidence of episodic AGN over a large range of time-scales have been discussed. The review closes with a discussion of open questions and prospects for the future. [ABSTRACT FROM AUTHOR]

This is a detailed spectral classification of 96 active galaxies from the Véron-Cetty and Véron catalog (2010, Version 13, VCV-13) of active galaxies and quasars. These objects were identified as radio sources using standard radio catalogs. Those galaxies which had radio sources in at least 6 different radio bands and had been identified spectrally in the SDSS catalog were selected. The types of activity of these were determined using their SDSS spectra. Three diagnostic diagrams and a direct study of the spectra were used for more certain classification. As a result, the classifications of 85% of the objects were changed. The radio sources in different radio bands make it possible to construct the spectral distribution of the energy in the radio range and to compare it with the optical activity types. [ABSTRACT FROM AUTHOR]

Millimeter- and submillimeter-wave maps are used to select potential candidate objects with the Sunyaev–Zeldovich effect in the vicinity of RCR (RATAN Cold Refined) radio sources. The properties of "hot" and "cold" spots in the right-ascension interval 2h ≤ RA ≤ 17h and the declination strip are studied. In the entire strip a total of 135 candidate objects with the Sunyaev–Zeldovich effect are found. A total of 86 objects are located within 7′ from RCR catalog sources. The effect shows up most conspicuously in the vicinity of 25 RCR sources. Clusters of galaxies or radio sources are found near the overwhelming majority of spots with the Sunyaev–Zeldovich effect. The distributions of radio spectral indices of the objects and the signal on microwave maps in the direction of radio sources are statistically analyzed. It is shown that when observed at microwave frequencies a number of objects are associated with sources with inverted spectra. [ABSTRACT FROM AUTHOR]

The paper presents the statistical data analysis of radio astronomic surveys in the sky region of a size of 177▭°at high galactic latitudes. We divided the region into four sectors equal in area and analyzed the observed properties of radio sources and the cosmic microwave background in each sector. The distribution of physical parameters (flux density, radio spectrum type, spectral index of radio sources) as well as the properties of the cosmic microwave background within the region of a size of 177▭° are shown to correspond to the cosmological principle, while the number of radio sources and their morphological types significantly differ in various areas. This points that studying sky regions of a given size, when analyzing the cosmic microwave background, can yield a statistically correct picture at high multipoles (corresponding to the size of a region), while generalization of the object calculations over the whole sky and their evolutionary morphological characteristics over the total population of sources is not obvious. We detected a positive shift in the response distribution in the direction to the radio sources on the cosmic microwave background map at the 2σ level repeated in all four sectors. According to the analysis of the multi-frequency Planck maps, a catalog has been compiled containing 120 new for galaxy cluster candidates with the Sunyaev—Zeldovich effect, 46 of which may be distant (z > 0.7). [ABSTRACT FROM AUTHOR]

Results of reducing and selecting data from the Ratan Zenith Field (RZF) are presented. A deep survey in the region 0h ≤ R.A. ≤ 24h, 40.5° ≤ DEC ≤ 42.5° carried out on the RATAN-600 radio telescope was used. Within +2′ of the center of the survey region, 448 objects were detected, 69 of them with ultra-steep spectra (USS). The SDSS digital optical survey (DR12), NVSS radio maps, and the FIRST catalogs have been used to cross-identify 208 radio sources from the RZF catalog, obtained as part of the "Genetic Code of the Universe" project. The characteristics of these objects are studied, and the distribution of the SDSS galaxies in a two-color diagram is obtained. Photometric redshifts and radio luminosities at 3940 and 1400 MHz are determined for 27 objects with spectral indices α < −1.1 (S ∝ να) for which magnitudes in various filters are presented in the SDSS. In the sample of USS objects, 12 galaxies have redshifts z < 0.5, are detected at wavelength λ = 7.6 cm, and have relatively high radio luminosities (type FR II or intermediate type FR I–FR II). Only one radio galaxy proved to be a rare nearby galaxy with relatively low radio luminosity L1400 MHz = 1.51 × 1024 W/Hz (type FR I). Two objects are candidate GHz-Peaked Spectrum objects. [ABSTRACT FROM AUTHOR]

The extragalactic sources of ultra-high-energy (E > 4 × 1019 eV) cosmic rays that make a small contribution to the flux of particles recorded by ground-based arrays are discussed. We show that cosmic rays from such sources can produce a noticeable diffuse gamma-ray flux in intergalactic space compared to the the data obtained with Fermi LAT (onboard the Fermi space observatory). A possible type of active galactic nuclei (AGNs) in which cosmi-ray protons can be accelerated to energies 1021 eV is considered as an illustration of such sources. We conclude that ultra-high-energy cosmic rays from the AGNs being discussed can contribute significantly to the extragalactic diffuse gamma-ray emission. In addition, a constraint on the fraction of the AGNs under consideration relative to the BL Lac objects and radio galaxies has been obtained from a comparison with the Fermi LAT data. [ABSTRACT FROM AUTHOR]

Jets in active galaxies are signatures of energy supply via collimated beams of plasma from the galactic nucleus to the extended regions of emission. These jets, which occur across the electromagnetic spectrum, are powered by supermassive black holes in the centres of the host galaxies. Jets are seen on the scale of parsecs in the nuclear regions to those which power the giant radio sources extending over several megaparsecs. These jets raise many challenging astrophysical questions. This article explores some aspects of jets in radio galaxies and quasars, which are amongst the most powerful active galaxies. [ABSTRACT FROM AUTHOR]

The spins of supermassive black holes in FR I and FR II radio galaxies are estimated using two models for the generation of the relativisitic jets, based on the Blandford-Znajek and Blandford-Payne mechanisms: the hybrid model ofMeier and a flux-trapping model. The magnetic field at the event horizon is estimated assuming equipartition between the energy densities of the magnetic field and the accreting material. The magnetic field near the inner edge of the accretion disk is estimated assuming equipartition between the magnetic pressure and the radiation pressure, and also assuming proportionality between the magnetic field and the spin. In the case of FR I objects, both mechanisms for the generation of the jets (the hybrid model ofMeier and a flux-trapping model) are efficient. For the FR II objects, equipartition between the energy densities of the magnetic field and the accretion flow facilitates stronger retrograde rotation of the supermassive black hole. Plots of spin versus mass suggest a predominantly chaotic character for the accretion in both types of radio galaxies. [ABSTRACT FROM AUTHOR]

A subclass of extragalactic radio sources known as winged radio galaxies has puzzled astronomers for many years. The wing features are detected at radio wavelengths as lowsurface- brightness radio lobes that are clearly misaligned with respect to the main lobe axis. Different models compete to account for these peculiar structures. Here, we report observational evidence that the parsec-scale radio jets in the Galactic microquasar GRS 1758-258 give rise to a Z-shaped radio emission strongly reminiscent of the X and Z-shaped morphologies found in winged radio galaxies. This is the first time that such extended emission features are observed in a microquasar, providing a new analogy for its extragalactic relatives. From our observations, we can clearly favour the hydrodynamic backflow interpretation against other possible wing formation scenarios. Assuming that physical processes are similar, we can extrapolate this conclusion and suggest that this mechanism could also be at work in many extragalactic cases. [ABSTRACT FROM AUTHOR]

Astrophysical sources such as radio halos and relics in galaxy clusters, supernova remnants and radio galaxies have angular sizes from a few to several 10s of arcminutes. In radio interferometric imaging of such sources, the largest angular size of the source that can be imaged is limited by the shortest projected baseline towards the source. It is essential to determine the limitations of the recovery of the extended features on various angular scales in order to interpret the radio image. We simulated observations of a model extended source of Gaussian shape with the Giant Metrewave Radio Telescope (GMRT) using Common Astronomy Software Applications (CASA). The recovery in flux density and in morphology of the model source was quantified in a variety of observing cases with changing source properties and the uv-coverage. If 휃 is the largest angular scale sampled in an observation with the GMRT, then > 80 % recovery of a source of size 0.3 × 휃 is possible. The upgraded GMRT (U-GMRT) providing 200 MHz instantaneous bandwidth between 300 - 500 MHz will allow a factor of two better recovery of a source of size 휃 as compared to the GMRT at 300 MHz with 33 MHz bandwidth. We provide quantitative estimates for the improvement in extended source recovery in observations at low elevations and long durations. The presented simulations can be carried out for future radio telescopes such as the Square Kilometre Array (SKA) for optimisation of observing strategies to image extended radio sources. [ABSTRACT FROM AUTHOR]

We suggest a method and build a model of radio galaxy distribution over the sphere using data from the WENSS catalogs and standard radio count models by Condon. We calculate the angular power spectrum of the contribution of extended radio galaxies into the microwave background and show that it can be a distorting factor for correct estimation of the angular spectrum from the signal determined by the Sunyaev-Zeldovich effect. [ABSTRACT FROM AUTHOR]

We examined the influence of environmental/intrinsic factors on the apparent asymmetries observed in the arm-lengths and luminosities of the lobes of double extragalactic radio sources. We showed that the observed arm-length ratio $( Q' ) $ is modified by environmental/intrinsic factors, which increases with increasing anisotropy in the environment. Also the modification seems higher for quasars than for FR-II radio galaxies. Using the power-law model of flux evolution in extragalactic radio sources, our analysis showed similar trend in the modification of observed lobe luminosity ratio by environmental/intrinsic factors. Our result also showed that the environmental influence on the observed asymmetries increases as radio source linear size decreases and seems higher for radio sources with observed lobe luminosity ratio ( $R<1$ ) than for radio sources with $R\geq 1$ . [ABSTRACT FROM AUTHOR]

The 'Big Trio' program is conducted at the Special Astrophysical Observatory of the Russian Academy of Sciences (SAO RAS) aiming to investigate a sample of sources with steep and ultra-steep spectra fromthe RCcatalog obtained on the basis of observational data of the 'Cold' survey. The population of distant FRII type radio galaxies with steep spectra is of particular interest, since new data indicate the presence of black holes with masses of more than 10 M which already formed in these giant stellar systems in the first billion years of life of the Universe, as well as their connection with emerging clusters. There are three sources with z > 3 in the sample. According to the observations of the 6-m SAO RAS telescope, the archival data of Subaru and Spitzer, an increased density of objects and several Ly α-emitters have been detected near one of the most powerful radio galaxies, RCJ0311+0507 (4C+04.11) with z = 4.51, which is the second most distant of the known FRII-type galaxies. Another object- RCJ1740+0502 with z = 3.57, is a possible dual AGN candidate. The third source, RCJ0105+0501, is an FRII-type galaxy ( z = 3.138) with a host galaxy of a complex structure, possibly generated by interaction in a close pair of galaxies. These radio sources have high radio luminosity ( L ≈ 10-10WHz), which requires the presence of a giant black hole with a sufficient accretion rate, and also with a rapid rotation, which in turn can be provided by major merging. [ABSTRACT FROM AUTHOR]

We carried out a comparative study on the dynamical properties of the Longer Arm (LA) and the Shorter Arm (SA) of different classes of FR-II radio sources (Broad Line Radio Galaxies (BLRG), Quasars (Q), Narrow Line Radio Galaxies (NLRG) and Low Excitation Radio Galaxies (LERG)) based on self-similar model of time evolution of the radio lobes and hotspot properties of radio sources, using the power-law expression for the dependence of hotspot size $(D_{\mathrm{hs}})$ , the advance velocity of the hotspot $(v_{\mathrm{hs}})$ and hotspot luminosity $(P_{\mathrm{L}})$ on the core-lobe length $(D_{\mathrm{L}})$ . Using observational values of $D_{\mathrm{hs}}$ , $P_{\mathrm{L}}$ and $D_{\mathrm{L}}$ we constrained the exponents of these power-law relations for the LA and SA. We also estimated the hotspot pressure, ( $p_{\mathrm{hs}}$ ), cocoon pressure within the lobe ( $p_{\mathrm{cc}}$ ), the ratio of the hotspot pressure to the cocoon pressure ( $p_{\mathrm{hc}}$ ), the cocoon volume ( $V\mathrm{cc}$ ), the energy density within the cocoon ( $u_{\mathrm{cc}}$ ), the equipartition magnetic field ( $B_{\mathrm{em}}$ ) in the lobe, the particle number density at the hotspot ( $n_{\mathrm{hs}}$ ), the external density profile $(\rho _{\mathrm{ext}})$ and the kinetic jet power ( $Q_{\mathrm{jet}}$ ) for the LA and the SA. Linear regression analyses indicate a tight correlation between the $D_{\mathrm{hs}}$ and the $D_{\mathrm{L}}$ of LA for all classes of radio sources with $r\sim0.5\mbox{--}0.8$ . Similar result was obtained for SA except for that of Q with $r\sim 0.2$ . For $P_{\mathrm{hs}}$ and $D_{\mathrm{L}}$ correlation, the result indicates a mild negative correlation that seems stronger for the SA ( $r\sim-0.3$ to −0.6) than LA ( $r\sim-0.2$ to −0.4) for all the different classes of radio sources. Comparing the values of $\rho_{\mathrm{ext}}$ , $B_{\mathrm{em}}$ , $u_{\mathrm{B}}$ , $p_{\mathrm{hs}}$ , $p_{\mathrm{cc}}$ , $V\mathrm{cc}$ , and $u_{\mathrm{cc}}$ between SA side and LA side, indicate that the SA values of the parameters are higher than those of LA; while $(p_{\mathrm{hs}})$ showed higher values in LA than SA for all the different classes of radio sources. Generally, the hotspot has a larger volume on the LA side than on the SA side except for NLRG, while the hotspot of the SA side contains more particle per unit volume than the LA side for Q, BLRG and LERG. Furthermore, Our results indicate that jet kinetic power is higher on the LA side for Q and NLRG but is smaller on the SA side for LERG, with the jet thrust generally higher on the LA side than o the SA side for all classes of radio sources. Generally, our analysis indicates that environmental factor plays an important role in the dynamics and evolution of double radio sources. [ABSTRACT FROM AUTHOR]

We review the results of HI line surveys of extragalactic sources in the local Universe. In the last two decades major efforts have been made in establishing on firm statistical grounds the properties of the HI source population, the two most prominent being the HI Parkes All Sky Survey and the Arecibo Legacy Fast ALFA survey. We review the choices of technical parameters in the design and optimization of spectro-photometric 'blind' HI surveys, which for the first time produced extensive HI-selected data sets. Particular attention is given to the relationship between optical and HI populations, the differences in their clustering properties and the importance of HI-selected samples in contributing to the understanding of apparent conflicts between observation and theory on the abundance of low mass halos. The last section of this paper provides an overview of currently ongoing and planned surveys which will explore the cosmic evolution of properties of the HI population. [ABSTRACT FROM AUTHOR]

We are pursuing a project to build a database of phase calibration sources suitable for Giant Metrewave Radio Telescope (GMRT). Here we present the first release of 45 low frequency calibration sources at 235 MHz and 610 MHz. These calibration sources are broadly divided into quasars, radio galaxies and unidentified sources. We provide their flux densities, models for calibration sources, ( u, v) plots, final deconvolved restored maps and clean-component lists/files for use in the Astronomical Image Processing System ( aips) and the Common Astronomy Software Applications ( casa). We also assign a quality factor to each of the calibration sources. These data products are made available online through the GMRT observatory website. In addition we find that (i) these 45 low frequency calibration sources are uniformly distributed in the sky and future efforts to increase the size of the database should populate the sky further, (ii) spectra of these calibration sources are about equally divided between straight, curved and complex shapes, (iii) quasars tend to exhibit flatter radio spectra as compared to the radio galaxies or the unidentified sources, (iv) quasars are also known to be radio variable and hence possibly show complex spectra more frequently, and (v) radio galaxies tend to have steeper spectra, which are possibly due to the large redshifts of distant galaxies causing the shift of spectrum to lower frequencies. [ABSTRACT FROM AUTHOR]

The study of galaxy protoclusters is beginning to fill in unknown details of the important phase of the assembly of clusters and cluster galaxies. This review describes the current status of this field and highlights promising recent findings related to galaxy formation in the densest regions of the early universe. We discuss the main search techniques and the characteristic properties of protoclusters in observations and simulations, and show that protoclusters will have present-day masses similar to galaxy clusters when fully collapsed. We discuss the physical properties of galaxies in protoclusters, including (proto-)brightest cluster galaxies, and the forming red sequence. We highlight the fact that the most massive halos at high redshift are found in protoclusters, making these objects uniquely suited for testing important recent models of galaxy formation. We show that galaxies in protoclusters should be among the first galaxies at high redshift making the transition from a gas cooling regime dominated by cold streams to a regime dominated by hot intracluster gas, which could be tested observationally. We also discuss the possible connections between protoclusters and radio galaxies, quasars, and $$\hbox {Ly}\alpha $$ blobs. Because of their early formation, large spatial sizes and high total star-formation rates, protoclusters have also likely played a crucial role during the epoch of reionization, which can be tested with future experiments that will map the neutral and ionized cosmic web. Lastly, we review a number of promising observational projects that are expected to make significant impact in this growing, exciting field. [ABSTRACT FROM AUTHOR]

The superfine structure of the object 3C 454.3 has been investigated at λ = 7 mm in polarized emission. The kinematics of the structure is shown to correspond to a vortex. A spiral structure like an Archimedes spiral has been established in the accretion disk. The orbital velocity of the inflow exceeds considerably the radial velocity. The disk is oriented in the plane of the sky. The bipolar outflow ejection axis is directed toward the observer with a slight inclination to the east. The jet sizes exceed considerably the counterjet sizes. The jet is ejected in a direction opposite to the observer; its apparent separation from the nozzle is determined by the disk shadowing. The counterjet is directed toward the observer; the flow brightness temperature at the exit from the nozzle reaches T ≈ 10 K. The jet has a spiral shape with an increasing pitch; the counterjet is a mirror reflection of the initial part of the jet. The incoming thermal plasma is accelerated and heated to relativistic temperatures as it is transferred along a spiral to the center. The orientation of the emission polarization plane changes along the flows due to a change in the ratio of the orbital and radial velocities, a change in the magnetic field orientation. [ABSTRACT FROM AUTHOR]

Associated with one of the most important forms of active galactic nucleus (AGN) feedback, and showing a strong preference for giant elliptical host galaxies, radio AGN ( $$L_{1.4\,\mathrm{GHz}} > 10^{24}$$ W $$\hbox {Hz}^{-1}$$ ) are a key sub-class of the overall AGN population. Recently their study has benefitted dramatically from the availability of high-quality data covering the X-ray to far-IR wavelength range obtained with the current generation of ground- and space-based telescope facilities. Reflecting this progress, here I review our current state of understanding of the population of radio AGN at low and intermediate redshifts ( $$z < 0.7$$ ), concentrating on their nuclear AGN and host galaxy properties, and covering three interlocking themes: the classification of radio AGN and its interpretation; the triggering and fuelling of the jet and AGN activity; and the evolution of the host galaxies. I show that much of the observed diversity in the AGN properties of radio AGN can be explained in terms of a combination of orientation/anisotropy, mass accretion rate, and variability effects. The detailed morphologies of the host galaxies are consistent with the triggering of strong-line radio galaxies (SLRG) in galaxy mergers. However, the star formation properties and cool ISM contents suggest that the triggering mergers are relatively minor in terms of their gas masses in most cases, and would not lead to major growth of the supermassive black holes and stellar bulges; therefore, apart from a minority (<20 %) that show evidence for higher star formation rates and more massive cool ISM reservoirs, the SLRG represent late-time re-triggering of activity in mature giant elliptical galaxies. In contrast, the host and environmental properties of weak-line radio galaxies (WLRG) with Fanaroff-Riley class I radio morphologies are consistent with more gradual fuelling of the activity via gas accretion at low rates onto the supermassive black holes. [ABSTRACT FROM AUTHOR]