Radio Luminosity Research Articles

Radio AGN in nearby dwarf galaxies: the important role of AGN in dwarf galaxy evolution

ABSTRACT We combine deep optical and radio data, from the Hyper Suprime-Cam and the Low-Frequency Array (LOFAR), respectively, to study 78 radio active galactic nuclei (AGN) in nearby (z < 0.5) dwarf galaxies. Comparison to a control sample, matched in stellar mass and redshift, indicates that the AGN and controls reside in similar environments, show similar star formation rates (which trace gas availability) and exhibit a comparable incidence of tidal features (which indicate recent interactions). We explore the AGN properties by combining the predicted gas conditions in dwarfs from a cosmological hydrodynamical simulation with a Monte Carlo suite of simulated radio sources, based on a semi-analytical model for radio-galaxy evolution. In the subset of LOFAR-detectable simulated sources, which have a similar distribution of radio luminosities as our observed AGN, the median jet powers, ages, and accretion rates are ∼1035 W, ∼5 Myr, and ∼10−3.4 M⊙ yr−1, respectively. The median mechanical energy output of these sources is ∼100 times larger than the median binding energy expected in dwarf gas reservoirs, making AGN feedback plausible. Since special circumstances (in terms of environment, gas availability, and interactions) are not necessary for the presence of AGN, and the central gas masses are predicted to be an order of magnitude larger than that required to fuel the AGN, AGN triggering in dwarfs is likely to be stochastic and a common phenomenon. Together with the plausibility of energetic feedback, this suggests that AGN could be important drivers of dwarf galaxy evolution, as is the case in massive galaxies.

FIRST J153350.8+272729: The Radio Afterglow of a Decades-old Tidal Disruption Event

Abstract We present the discovery of the fading radio transient FIRST J153350.8+272729. The source had a maximum observed 5 GHz radio luminosity of 8 × 1039 erg s−1 in 1986, but by 2019 had faded by a factor of nearly 400. It is located at the center of a galaxy (SDSS J153350.89+272729) at 147 Mpc, which shows weak Type II Seyfert activity. We show that a tidal disruption event (TDE) is the preferred scenario for FIRST J153350.8+272729, although it could plausibly be interpreted as the afterglow of a long-duration γ-ray burst. This is only the second TDE candidate to be first discovered at radio wavelengths. Its luminosity fills a gap between the radio afterglows of subrelativistic TDEs in the local universe, and relativistic TDEs at high redshifts. The unusual properties of FIRST J153350.8+272729 (ongoing nuclear activity in the host galaxy, high radio luminosity) motivate more extensive TDE searches in untargeted radio surveys.

A Wide and Deep Exploration of Radio Galaxies with Subaru HSC (WERGS). VI. Distant Filamentary Structures Pointed Out by High-z Radio Galaxies at z ∼ 4

Abstract We present the environmental properties around high-z radio galaxies (HzRGs) at z ∼ 4, which have been poorly investigated because of their rarity. We use the largest samples of HzRGs and g-dropout galaxy overdense regions at z ∼ 4, which were constructed from the Hyper Suprime-Cam Subaru Strategic Program, to characterize the HzRG environments statistically. We measure the g-dropout galaxy overdensities around 21 HzRGs whose rest-frame 1.4 GHz radio luminosities (L 1.4 GHz) are 1026–27 W Hz−1. We find that the overdensities around the faint HzRGs with L 1.4 GHz ∼ 1026.0–26.5 W Hz−1 tend to be higher than those of the g-dropout galaxies. On the other hand, no significant difference of density environments is found between the luminous HzRGs with L 1.4 GHz ∼ 1026.5–27.0 W Hz−1 and the g-dropout galaxies. The HzRGs are found to occupy more massive halos than g-dropout galaxies through a cross-correlation between the HzRGs and g-dropout galaxies. This trend is more pronounced in the faint HzRGs. These results are consistent with a scenario where HzRGs get older and more massive as the radio luminosity decreases. The HzRGs are expected to trace the progenitors of Local Cluster halos from their calculated halo mass. In addition, we find that surrounding galaxies tend to distribute along the radio jet major axis of the HzRGs at angular distances of ≲500 physical kpc. Our findings imply the onset of the filamentary structures around the HzRGs at z ∼ 4.

Searching for Stellar and Planetary Emission in Large Field-of-view Radio Sky Surveys

Abstract Detection of low-frequency (≤1.4 GHz) radio emission from stellar and planetary systems can lead to new insights into stellar activity, extrasolar space weather, and planetary magnetic fields. In this work, we investigate three large field-of-view surveys at 74 MHz, 150 MHz, and 1.4 GHz, as well as a myriad of multiwavelength ancillary data, to search for radio emission from about 2600 stellar objects, including about 800 exoplanetary systems, 600 nearby low-mass stars, and 1200 young stellar objects located in the Taurus and Upper Scorpius star-forming regions. The selected sample encompasses stellar spectral types from B to L and distances between 5 and 300 pc. We report the redetection of five stars at 1.4 GHz, one of which also shows emission at 150 MHz. Four of these are low- and intermediate-mass young stars, and one is the evolved star α Sco. We also observe radio emission at the position of a young brown dwarf at 1.4 GHz and 150 MHz. However, due to the large astrometric uncertainty of radio observations, a follow-up study at higher angular resolution would be required to confirm whether the observed emission originates from the brown dwarf itself or a background object. Notably, all of the selected radio sources are located in nearby star-forming regions. Furthermore, we use image stacking and statistical methods to derive upper limits on the average quiescent radio luminosity of the families of objects under investigation. These analyses provide observational constraints for large-scale searches for current and ongoing low-frequency radio emissions from stars and planets.

Peculiar Radio–X-Ray Relationship in Active Stars

Abstract The empirical relationship between the nonthermal 5 GHz radio luminosity and the soft X-ray luminosity of active stellar coronae, canonically called the Güdel–Benz relationship, has been a cornerstone of stellar radio astronomy, as it explicitly ties the radio emission to the coronal heating mechanisms. The relationship extends from microflares on the Sun to the coronae of the most active stars suggesting that active coronae are heated by a flare-like process. The relationship is thought to originate from a consistent partition of the available flare energy into relativistic charges, which emit in the radio-band via the incoherent gyrosynchrotron mechanism, and heating of the bulk coronal plasma, which emits in the X-ray band via the Bremsstrahlung mechanism. Consequently, coherent emission from stellar and substellar objects is not expected to adhere to this empirical relationship, as it is observed in ultracool dwarf stars and brown dwarfs. Here we report a population of radio-detected chromospherically active stars that surprisingly follow the Güdel–Benz relationship despite their radio emission being classified as coherent emission by virtue of its high circularly polarized fraction and high brightness temperature. Our results prompt a reexamination of the physics behind the Güdel–Benz relationship, its implication for the mechanism of coronal heating and particle acceleration in active stars, and the phenomenological connection between solar and stellar flares.

Searching for anomalous microwave emission in nearby galaxies

Aims. We observed four nearby spiral galaxies (NGC 3627, NGC 4254, NGC 4736, and NGC 5055) in the K band with the 64-m Sardinia Radio Telescope, with the aim of detecting anomalous microwave emission (AME), a radiation component presumably due to spinning dust grains, which has been observed thus far in the Milky Way and only in a handful of other galaxies (most notably, M 31). Methods. We mapped the galaxies at 18.6 and 24.6 GHz and studied their global photometry together with other radio-continuum data from the literature in order to find AME as emission in excess of the synchrotron and thermal components. Results. We only found upper limits for AME. These nondetections, and other upper limits in the literature, are nevertheless consistent with the average AME emissivity from a few detections: it is ϵ30 GHzAME = 2.4 ± 0.4 × 10−2 MJy sr−1 (M⊙ pc−2)−1 in units of dust surface density (equivalently, 1.4 ± 0.2 × 10−18 Jy sr−1 (H cm−2)−1 in units of H column density). We finally suggest searching for AME in quiescent spirals with relatively low radio luminosity, such as M 31.

Beaming Effect in Fermi Blazars

Abstract Blazars show extreme observational properties that are due to the beaming effect with the jet being close to the line of sight. It was found that the observed luminosity is anticorrelated with the synchrotron peak frequency but the debeamed luminosity and the frequency is positively correlated. In this work, we revisit this correlation for a large sample of 255 blazars from the fourth Fermi catalog with available Doppler factors. Our analysis comes to the following conclusions. (1) The observed radio, X-ray, γ-ray, and synchrotron peak luminosity are all anticorrelated with the peak frequency, but the debeamed luminosity is positively correlated with the debeamed peak frequency. The anticorrelation is due to a selection effect or a beaming effect. (2) The Compton dominance parameter is correlated with both the bolometric luminosity and Doppler factor, implying that the more highly Compton-dominated sources are more luminous. (3) The bolometric luminosity can be represented by the γ-ray luminosity for Fermi blazars.

LoTSS jellyfish galaxies

In this paper we report the first identification of jellyfish galaxies in the Perseus cluster (Abell 426). We identified four jellyfish galaxies (LEDA 2191078, MCG +07-07-070, UGC 2654, UGC 2665) within the central 2° ×2° (2.6 Mpc × 2.6 Mpc) of Perseus based on the presence of one-sided radio continuum tails that were detected at 144 MHz by the LOw Frequency ARray (LOFAR). The observed radio tails, as well as the orientation of morphological features in the rest-frame optical, are consistent with these four galaxies being impacted by ram pressure stripping as they orbit through the Perseus intracluster medium. By combining the LOFAR imaging at 144 MHz with 344 MHz imaging from the Karl G. Jansky Very Large Array, we derived spectral indices for the disks and the stripped tails of these jellyfish galaxies. We show that the spectral indices over the galaxy disks are quite flat, while the indices of the stripped tails are substantially steeper. We also identified a number of compact Hα + [NII] sources with narrowband imaging from the Isaac Newton Telescope. These sources are brighter along the leading side of the galaxy (i.e., opposite to the direction of the stripped tail), which is consistent with ram pressure induced star formation. Lastly, consistent with previous works in other clusters, we find that these jellyfish galaxies show enhanced radio luminosities for their observed star formation rates. Given the small distance to the Perseus cluster (D ∼ 70 Mpc, 1″ ≃ 340 pc), these galaxies are excellent candidates for multiwavelength follow-up observations to probe the impact of ram pressure stripping on galaxy star formation at subkiloparsec scales.

The radio dichotomy of active galactic nuclei

Abstract The question of radio dichotomy in active galactic nuclei (AGNs) is still in debate, even though it has been discussed for more than 40 years. In order to solve this old riddle, we collect a sample of AGNs with optical B band and radio 6 cm wavelength data to analyze the radio loudness log R. Our results indicate a separation of log R = 〈1.37 ± 0.02〉 between radio-loud (RL) AGNs and radio-quiet (RQ) AGNs, suggesting the existence of an RL/RQ dichotomy. For the first time, we suggest combining radio luminosity and radio loudness as a double criterion to divide AGNs into RLs and RQs to avoid misclassification problems that may happen in the single-criterion scenario; we propose the double-criterion dividing line log L6 cm = −2.7log R + 44.3 by using a machine-learning method. In addition, the key point of the RL/RQ dichotomy is the origin of radio emission for the two classes, and we suggest the radio emission from RLs and RQs share the same origin, e.g., jets and mini-jets (aborted-jet or outflow), through a correlation study between radio 6 cm luminosity and optical B-band luminosity.

Infrared-radio relation in the local Universe

Context.The Square Kilometer Array (SKA) is expected to detect high-redshift galaxies with star formation rates (SFRs) up to two orders of magnitude lower thanHerschelsurveys and will thus boost the ability of radio astronomy to study extragalactic sources. The tight infrared-radio correlation offers the possibility of using radio emission as a dust-unobscured star formation diagnostic. However, the physics governing the link between radio emission and star formation is poorly understood, and recent studies have pointed to differences in the exact calibration required when radio is to be used as a star formation tracer.Aims.We improve the calibration of the relation of the local radio luminosity–SFR and to test whether there are nonlinearities in it.Methods.We used a sample ofHerschelAstrophysical Terahertz Large Area Survey (H-ATLAS) sources and investigated their radio luminosity, which was derived using the NRAO VLA Sky Survey (NVSS) and Faint Images of the Radio Sky at Twenty-cm (FIRST) maps. We stacked the bins of infrared luminosity and SFR and accounted for bins with no detections in the stacked images using survival analysis fitting. This approach was tested using Monte Carlo simulations.Results.After removing sources from the sample that have excess radio emission, which is indicative of nuclear radio activity, we found no deviations from linearity of the mean relations between radio luminosity and either SFR or infrared luminosity.Concluisions.We analyzed the link between radio emission and SFR or infrared luminosity using a local sample of star-forming galaxies without evidence of nuclear radio activity and found no deviations from linearity, although our data are also consistent with the small nonlinearity reported by some recent analyses. The normalizations of these relations are intermediate between those reported by earlier works.

BASS XXXI: Outflow scaling relations in low redshift X-ray AGN host galaxies with MUSE

ABSTRACT Ionized gas kinematics provide crucial evidence of the impact that active galactic nuclei (AGNs) have in regulating star formation in their host galaxies. Although the presence of outflows in AGN host galaxies has been firmly established, the calculation of outflow properties such as mass outflow rates and kinetic energy remains challenging. We present the [O iii]λ5007 ionized gas outflow properties of 22 z<0.1 X-ray AGN, derived from the BAT AGN Spectroscopic Survey using MUSE/VLT. With an average spatial resolution of 1 arcsec (0.1–1.2 kpc), the observations resolve the ionized gas clouds down to sub-kiloparsec scales. Resolved maps show that the [O iii] velocity dispersion is, on average, higher in regions ionized by the AGN, compared to star formation. We calculate the instantaneous outflow rates in individual MUSE spaxels by constructing resolved mass outflow rate maps, incorporating variable outflow density and velocity. We compare the instantaneous values with time-averaged outflow rates by placing mock fibres and slits on the MUSE field-of-view, a method often used in the literature. The instantaneous outflow rates (0.2–275 M⊙ yr−1) tend to be two orders of magnitude higher than the time-averaged outflow rates (0.001–40 M⊙ yr−1). The outflow rates correlate with the AGN bolometric luminosity (Lbol ∼ 1042.71–1045.62 erg s−1) but we find no correlations with black hole mass (106.1–108.9 M⊙), Eddington ratio (0.002–1.1), and radio luminosity (1021–1026 W Hz−1). We find the median coupling between the kinetic energy and Lbol to be 1 per cent, consistent with the theoretical predictions for an AGN-driven outflow.

Optical properties of Peaked Spectrum radio sources

ABSTRACT In this work, we study the optical properties of compact radio sources selected from the literature in order to determine the impact of the radio-jet in their circumnuclear environment. Our sample includes 58 Compact Steep Spectrum (CSS) and GigaHertz Peaked Spectrum (GPS) and 14 Megahertz-Peaked spectrum (MPS) radio sources located at z ≤ 1. The radio luminosity (LR) of the sample varies between Log LR ∼ 23.2 and 27.7 W Hz−1. We obtained optical spectra for all sources from SDSS-DR12 and performed a stellar population synthesis using the starlight code. We derived stellar masses (M⋆), ages 〈t⋆〉, star formation rates (SFR), metallicities 〈Z⋆〉 and internal reddening AV for all young AGNs of our sample. A visual inspection of the SDSS images was made to assign a morphological class for each source. Our results indicate that the sample is dominated by intermediate to old stellar populations and there is no strong correlation between optical and radio properties of these sources. Also, we found that young AGNs can be hosted by elliptical, spiral and interacting galaxies, confirming recent findings. When comparing the optical properties of CSS/GPS and MPS sources, we do not find any significant difference. Finally, the Mid-Infrared WISE colours analysis suggests that the compact radio sources defined as powerful AGNs are, in general, gas-rich systems.

Exploring the physics behind the non-thermal emission from star-forming galaxies detected in γ rays

Context. Star-forming galaxies emit non-thermal radiation from radio to γ rays. Observations show that their radio and γ-ray luminosities scale with their star formation rates, supporting the hypothesis that non-thermal radiation is emitted by cosmic rays produced by their stellar populations. However, the nature of the main cosmic-ray transport processes that shape the emission in these galaxies is still poorly understood, especially at low star formation rates. Aims. Our aim is to investigate the main mechanisms of global cosmic-ray transport and cooling in star-forming galaxies. The way they contribute to shaping the relations between non-thermal luminosities and star formation rates could shed light onto their nature, and allow us to quantify their relative importance at different star formation rates. Methods. We developed a model to compute the cosmic-ray populations of star-forming galaxies, taking into account their production, transport, and cooling. The model is parametrised only through global galaxy properties, and describes the non-thermal emission in radio (at 1.4 GHz and 150 MHz) and γ rays (in the 0.1−100 GeV band). We focused on the role of diffusive and advective transport by galactic winds, either driven by turbulent or thermal instabilities. We compared model predictions to observations, for which we compiled a homogeneous set of luminosities in these radio bands, and updated those available in γ rays. Results. Our model reproduces reasonably well the observed relations between the γ-ray or 1.4 GHz radio luminosities and the star formation rate, assuming a single power-law scaling of the magnetic field (with index β = 0.3) and winds blowing either at Alfvenic speeds (∼tens of km s−1, for ≲5 M⊙ yr−1) or typical starburst wind velocities (∼hundreds of km s−1, for ≳5 M⊙ yr−1). Escape of cosmic rays is negligible for ≳30 M⊙ yr−1. A constant ionisation fraction of the interstellar medium fails to reproduce the 150 MHz radio luminosity throughout the whole star formation rate range. Conclusions. Our results reinforce the idea that galaxies with high star formation rates are cosmic-ray calorimeters, and that the main mechanism driving proton escape is diffusion, whereas electron escape also proceeds via wind advection. They also suggest that these winds should be cosmic-ray or thermally driven at low and intermediate star formation rates, respectively. Our results globally support that magneto-hydrodynamic turbulence is responsible for the dependence of the magnetic field strength on the star formation rate and that the ionisation fraction is strongly disfavoured to be constant throughout the whole range of star formation rates.

Final Moments. I. Precursor Emission, Envelope Inflation, and Enhanced Mass Loss Preceding the Luminous Type II Supernova 2020tlf

Abstract We present panchromatic observations and modeling of supernova (SN) 2020tlf, the first normal Type II-P/L SN with confirmed precursor emission, as detected by the Young Supernova Experiment transient survey. Pre-SN activity was detected in riz-bands at −130 days and persisted at relatively constant flux until first light. Soon after discovery, “flash” spectroscopy of SN 2020tlf revealed narrow, symmetric emission lines that resulted from the photoionization of circumstellar material (CSM) shed in progenitor mass-loss episodes before explosion. Surprisingly, this novel display of pre-SN emission and associated mass loss occurred in a red supergiant (RSG) progenitor with zero-age main-sequence mass of only 10–12 M ⊙, as inferred from nebular spectra. Modeling of the light curve and multi-epoch spectra with the non-LTE radiative-transfer code CMFGEN and radiation-hydrodynamical code HERACLES suggests a dense CSM limited to r ≈ 1015 cm, and mass-loss rate of 10−2 M ⊙ yr−1. The luminous light-curve plateau and persistent blue excess indicates an extended progenitor, compatible with an RSG model with R ⋆ = 1100 R ⊙. Limits on the shock-powered X-ray and radio luminosity are consistent with model conclusions and suggest a CSM density of ρ < 2 × 10−16 g cm−3 for distances from the progenitor star of r ≈ 5 × 1015 cm, as well as a mass-loss rate of M ̇ < 1.3 × 10 − 5 M ☉ yr − 1 at larger distances. A promising power source for the observed precursor emission is the ejection of stellar material following energy disposition into the stellar envelope as a result of gravity waves emitted during either neon/oxygen burning or a nuclear flash from silicon combustion.

The relation between the radio emission of the core and host galaxy properties in Fanaroff–Riley type II radio galaxies

AbstractWe study the radio power of the core and its relation to the optical properties of the host galaxy in samples of high-excitation (HERG) and low-excitation (LERG) Fanaroff–Riley type II (FRII) radio galaxies. The radio galaxy sample is divided into two groups of core/non-core FRII, based on the existence of strong, weak or lack of single radio core component. We show that FRII LERGs with radio emission of the core have significantly higher [O III] line luminosities compared to the non-core LERG FRIIs. There is no significant difference between the hosts of the core and non-core FRIIs of LERG type in galaxy sizes, concentration indices, star formation rates, 4000-Å break strengths, colours, black hole masses, and black hole to stellar masses. We show that the results are not biased by the stellar masses, redshifts, and angular sizes of the radio galaxies. We argue that the detection of higher [O III] luminosities in the core FRIIs may indicate the presence of higher amounts of gas, very close to the active galactic nuclei (AGN) nucleus in the core FRIIs compared to the non-core FRIIs or may result from the interaction of the radio jets with this gas. The core and non-core FRIIs of the HERG type show no significant differences perhaps due to our small sample size. The effect of relativistic beaming on the radio luminosities and the contribution of restating AGN activity have also been considered.

HERA Phase I Limits on the Cosmic 21 cm Signal: Constraints on Astrophysics and Cosmology during the Epoch of Reionization

Abstract Recently, the Hydrogen Epoch of Reionization Array (HERA) has produced the experiment’s first upper limits on the power spectrum of 21 cm fluctuations at z ∼ 8 and 10. Here, we use several independent theoretical models to infer constraints on the intergalactic medium (IGM) and galaxies during the epoch of reionization from these limits. We find that the IGM must have been heated above the adiabatic-cooling threshold by z ∼ 8, independent of uncertainties about IGM ionization and the radio background. Combining HERA limits with complementary observations constrains the spin temperature of the z ∼ 8 neutral IGM to 27 K 〈 T ¯ S 〉 630 K (2.3 K 〈 T ¯ S 〉 640 K) at 68% (95%) confidence. They therefore also place a lower bound on X-ray heating, a previously unconstrained aspects of early galaxies. For example, if the cosmic microwave background dominates the z ∼ 8 radio background, the new HERA limits imply that the first galaxies produced X-rays more efficiently than local ones. The z ∼ 10 limits require even earlier heating if dark-matter interactions cool the hydrogen gas. If an extra radio background is produced by galaxies, we rule out (at 95% confidence) the combination of high radio and low X-ray luminosities of L r,ν /SFR > 4 × 1024 W Hz−1 M ⊙ − 1 yr and L X /SFR < 7.6 × 1039 erg s−1 M ⊙ − 1 yr. The new HERA upper limits neither support nor disfavor a cosmological interpretation of the recent Experiment to Detect the Global EOR Signature (EDGES) measurement. The framework described here provides a foundation for the interpretation of future HERA results.

Discovery of a Double Radio Relic in ZwCl1447.2+2619: A Rare Testbed for Shock-acceleration Models with a Peculiar Surface-brightness Ratio

Abstract We report a discovery of a double radio relic in the cluster merger ZwCl1447.2+2619 (z = 0.376) with uGMRT observations at 420 MHz and 700 MHz. The linear sizes of the northern and southern relics are ∼0.3 Mpc and ∼1.2 Mpc, respectively, which is consistent with the theoretical expectation that a larger relic is produced in the less massive subcluster side. However, ZwCl1447.2+2619 is unlike other known double radio relic systems, where the larger relics are much more luminous by several factors. In this merger, the higher surface brightness of the smaller northern relic makes its total radio luminosity comparable to that of the much larger southern relic. The surface brightness ratio ∼0.1 between the two radio relics differs significantly from the relation observed in other double radio relic systems. From our radio spectral analysis, we find that both relics signify similar weak shocks with Mach numbers of 2.9 ± 0.8 and 2.0 ± 0.7 for the northern and southern relics, respectively. Moreover, the northern relic is connected to a discrete radio source with an optical counterpart, which indicates the possible presence of cosmic-ray injection and reacceleration. Therefore, we propose that this atypical surface brightness ratio can be explained with the particle acceleration efficiency precipitously dropping in the weak shock regime and/or with reacceleration of fossil cosmic rays. Our multi-wavelength analysis and numerical simulation suggest that ZwCl1447.2+2619 is a postmerger, which has experienced a near head-on collision ∼0.7 Gyr ago.

Finding Rare Quasars: VLA Snapshot Continuum Survey of FRI Quasar Candidates Selected from the LOFAR Two-Metre Sky Survey (LoTSS)

The radiative and jet power in active galactic nuclei is generated by accretion of material on to supermassive galactic-centre black holes. For quasars, where the radiative power is by definition very high, objects with high radio luminosities form 10 per cent of the population, although it is not clear whether this is a stable phase. Traditionally, quasars with high radio luminosities have been thought to present jets with edge-brightened morphology (Fanaroff-Riley II—FR II) due to the limitations of previous radio surveys (i.e., FRIs were not observed as part of the quasar population). The LOw Frequency ARray (LOFAR) Two-metre Sky Survey (LoTSS) with its unprecedented sensitivity and resolution covering wide sky areas has enabled the first systematic selection and investigation of quasars with core-brightened morphology (Fanaroff-Riley I—FR). We carried out a Very Large Array (VLA) snapshot survey to reveal inner structures of jets in selected quasar candidates; 15 (25 per cent) out of 60 sources show clear inner jet structures that are diagnostic of FRI jets and 13 quasars (∼22 per cent) show extended structures similar to those of FRI jets. Black hole masses and Eddington ratios do not show a clear difference between FRI and FRII quasars. FRII quasars tend to have higher jet powers than FRI quasars. Our results show that the occurrence of FRI jets in powerful radiatively efficient systems is not common, probably mainly due to two factors: galaxy environment and jet power.

The Photometric and Spectroscopic Properties of Remnant and Restarted Radio Galaxies in the Lockman Hole Field

Radio galaxies are known to undergo phases of activity, where the stage after the jets have switched off is referred to as the remnant phase. This state can be followed by a restarted phase when the activity reignites. Remnant and restarted radio sources are important for testing models of the evolution of radio active galactic nuclei (AGN) and for understanding the impact the recurrent jet activity has on their host galaxies. Although we now have statistical samples of radio sources in various stages of their life cycle, how this intermittent radio activity is reflected in the optical properties in this sample has not yet been addressed, and is overall a much less studied aspect in the literature. In this work, we use the Wide-field Infrared Survey Explorer and the Sloan Digital Sky Survey (SDSS) photometry, and SDSS spectra to study these properties in a sample of the remnant, candidate restarted, and active radio galaxies selected using the LOw Frequency ARray at 150 MHz in the Lockman Hole extragalactic field. Within the range of radio luminosities and stellar masses studied in this work, we find no difference between the properties of the host galaxy and of the optical emission lines for objects in different phases of their radio life cycle. The vast majority of our radio sources (either remnant, candidate restarted, or comparison sample) are associated with radiatively inefficient optical AGN and red galaxies dominated by old stellar populations. Thus, the radio and emission-line AGN activity appears to be independent and regulated by different mechanisms. This suggests that, at least for the radio luminosities of our sample, the life cycle of the radio may depend on intrinsic reasons, such as the stability of the accretion disc, more than variation in the accretion rate and fuelling of the central black hole.

Radio continuum properties of OH megamaser galaxies

ABSTRACT We present a study of the radio continuum properties of two luminous/ultraluminous infrared galaxy samples: the OH megamaser (OHM) sample (74 objects) and the control sample (128 objects) without detected maser emission. We carried out pilot observations for 140 objects with the radio telescope RATAN-600 at 1.2, 2.3, 4.7, 8.2, 11.2, and 22.3 GHz in 2019–2021. The OHM sample has two times more flat-spectrum sources (32 per cent) than the control sample. Steep radio spectra prevail in both samples. The median spectral index at 4.7 GHz α4.7 = −0.59 for the OHM sample, and α4.7 = −0.71 for the non-OHM galaxies. We confirm a tight correlation of the far-infrared (FIR) and radio luminosities for the OHM sample. We found correlations between isotropic OH line luminosity LOH and the spectral index α4.7 (ρ = 0.26, p-val. = 0.04) and between LOH and radio luminosity P1.4 (ρ = 0.35, p-val. = 0.005). Reviewing subsamples of masers powered by active galactic nuclei (AGNs) and star formation revealed insignificant differences for their FIR and radio properties. None the less, AGN-powered galaxies exhibit larger scatter in a range of parameters and their standard deviations. The similarities in the radio and FIR properties in the two samples are presumably caused by the presence of a significant amount of AGN sources in both samples (47 and 30 per cent in the OHM and control samples) and/or possibly by the presence of undetected OH emission sources in the control sample.