Nuclear Radio Research Articles

Prevalence of Compact Nuclear Radio Emission in Post-merger Galaxies and Its Origin

Post-merger galaxies are unique laboratories to study the triggering and interplay of star formation and active galactic nucleus (AGN) activity. Combining new, high-resolution Jansky Very Large Array (VLA) observations with archival radio surveys, we have examined the radio properties of 28 spheroidal post-merger galaxies. We detect 18 radio sources in our post-merger sample and find a general lack of extended emission at (sub)kiloparsec scales, indicating the prevalence of compact, nuclear radio emission in these post-merger galaxies, with the majority (16/18; 89%) characterized as low luminosity. Using multiwavelength data, we determine the origin of the radio emission, discovering 15 new radio AGNs and three radio sources likely associated with star-forming (SF) processes. Among the radio AGNs, almost all are low luminosity (13/15; 87%), inconsistent with a relativistic jet origin. We discover a new dual AGN (DAGN) candidate, J1511+0417, and investigate the radio properties of the DAGN candidate J0843+3549. Five of these radio AGNs are hosted by a SF or SF-AGN composite emission-line galaxy, suggesting that radio AGN activity may be present during periods of SF activity in post-mergers. The low-power jets and compact morphologies of these radio AGNs also point to a scenario in which AGN feedback may be efficient in this sample of post-mergers. Lastly, we present simulated, multifrequency observations of the 15 radio AGNs with the Very Long Baseline Array and the very-long-baseline interferometry capabilities of the Next-Generation VLA to assess the feasibility of these instruments in searches for supermassive black hole binaries.

On the Subparsec-scale Core Composition of FR 0 Radio Galaxies

Although Fanaroff–Riley type 0 (FR 0) radio galaxies are known to be the most numerous jet population in the local Universe, they are much less explored than the well-established class of FR type I (FR I) and FR type II galaxies due to their intrinsic weakness. Observationally, their nuclear radio, optical, and X-ray properties are comparable to the nuclear environment of FR Is. The recent detection of two FR 0s in the high-energy band suggests that, like in FR Is, charged particles are accelerated there to energies that enable gamma-ray production. Up to now, only the lack of extended radio emission from FR 0s distinguishes them from FR Is. By comparing the spectral energy distribution of FR 0s with that of FR Is and in particular with that of M87 as a well-studied reference source of the FR I population, we find the broadband spectrum of FR 0 s exceptionally close to M87's quiet core emission. Relying on that similarity, we apply a lepto-hadronic jet-accretion flow model to FR 0s. This model is able to explain the broadband spectral energy distribution, with parameters close to particle-field equipartition and matching all observational constraints. In this framework, FR 0s are multimessenger jet sources, with a nature and highly magnetized environment similar to those of the naked quiet core of FR Is.

The Nascent Milliquasar VT J154843.06+220812.6: Tidal Disruption Event or Extreme Accretion State Change?

We present a detailed multiwavelength follow-up of the nuclear radio flare VT J154843.06+220812.6, hereafter VT J1548. VT J1548 was selected as a ∼1 mJy radio flare in 3 GHz observations from the Very Large Array Sky Survey. It is located in the nucleus of a low-mass () host galaxy with weak or no past active galactic nuclei (AGN) activity. VT J1548 is associated with a slow rising (multiple year), bright mid-IR flare in the Wide-field Infrared Survey Explorer survey, peaking at ∼10%L edd.. No associated optical transient is detected, although we cannot rule out a short, early optical flare given the limited data available. Constant late-time (∼3 yr post-flare) X-ray emission is detected at ∼1042 erg s−1. The radio spectral energy distribution is consistent with synchrotron emission from an outflow incident on an asymmetric medium. A follow-up, optical spectrum shows transient, bright, high-ionization coronal line emission ([Fe x i] λ6375, [Fe x i] λ7894, [S x i i] λ7612). Transient broad Hα is also detected but without corresponding broad Hβ emission, suggesting high nuclear extinction. We interpret this event as either a tidal disruption event or an extreme flare of an AGN, in both cases obscured by a dusty torus. Although these individual properties have been observed in previous transients, the combination is unprecedented. This event highlights the importance of searches across all wave bands for assembling a sample of nuclear flares that spans the range of observable properties and possible triggers.

Light-curve Evolution of the Nearest Tidal Disruption Event: A Late-time, Radio-only Flare

Abstract Tidal disruption events (TDEs) occur when a star passes close enough to a galaxy’s supermassive black hole to be disrupted by tidal forces. We discuss new observations of IGRJ12580+0134, a TDE observed in NGC 4845 (d = 17 Mpc) in 2010 November, with the Karl G. Jansky Very Large Array (VLA 9 9 The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. ). We also discuss a reanalysis of 2010–2011 Swift and XMM-Newton observations, as well as new, late-time Swift observations. Our JVLA observations show a decay of the nuclear radio flux until 2015, when a plateau was seen, and then a significant (factor ∼3) radio flare during 2016. The 2016 radio flare was also accompanied by radio spectral changes, but was not seen in the X-rays. We model the flare as resulting from the interaction of the nuclear jet with a cloud in the interstellar medium. This is distinct from late-time X-ray flares in a few other TDEs where changes in the accretion state and/or a fallback event were suggested, neither of which appears possible in this case. Our reanalysis of the Swift and XMM-Newton data from 2011 shows significant evidence for thermal emission from a disk, as well as a very soft power law. This, in addition to the extreme X-ray flux increase seen in 2010 (a factor of >100) bolsters the identification of IGRJ12580+0134 as a TDE, not an unusual active galactic nucleus variability event.

A new distant giant radio galaxy in the Boötes field serendipitously detected by Chandra

Context. Giant radio galaxies (GRGs) are the largest single structures in the Universe. Exhibiting extended radio morphology, their projected sizes range from 0.7 Mpc up to 4.9 Mpc. LOFAR has opened a new window on the discovery and investigation of GRGs and, despite the hundreds that are known today, their main growth catalyst is still under debate. Aims. One natural explanation for the exceptional size of GRGs is their old age. In this context, hard X-ray selected GRGs show evidence of restarting activity, with the giant radio lobes being mostly disconnected from the nuclear source, if any are present at all. In this paper, we present the serendipitous discovery of a distant (z = 0.629), medium X-ray-selected GRG in the Boötes field. Methods. High-quality, deep Chandra and LOFAR data allow for a robust study of the connection between the nucleus and the lobes, at a larger redshift, which has thus far been inaccessible to coded-mask hard X-ray instruments. Results. The radio morphology of the GRG presented in this work does not show evidence for restarted activity and the nuclear radio core spectrum does not appear to be gigahertz-peaked spectrum (GPS)-like. On the other hand, the X-ray properties of the new GRG are perfectly consistent with the ones previously studied with Swift/BAT and INTEGRAL at lower redshift. In particular, the bolometric luminosity measured from the X-ray spectrum is a factor of six larger than the one derived from the radio lobes, although the large uncertainties make them formally consistent at 1σ. Finally, the moderately dense environment around the GRG, traced by the spatial distribution of galaxies, supports recent findings that the growth of GRGs is not primarily driven by underdense environments.

The nearby extreme accretion and feedback system PDS 456: finding a complex radio-emitting nucleus

ABSTRACT When a black hole accretes close to the Eddington limit, the astrophysical jet is often accompanied by radiatively driven, wide-aperture and mildly relativistic winds. Powerful winds can produce significant non-thermal radio emission via shocks. Among the nearby critical accretion quasars, PDS 456 has a very massive black hole (about 1 billion solar masses), shows a significant star-forming activity (about 70 solar masses per year), and hosts exceptionally energetic X-ray winds (power up to 20 per cent of the Eddington luminosity). To probe the radio activity in this extreme accretion and feedback system, we performed very long baseline interferometric (VLBI) observations of PDS 456 at 1.66 GHz with the European VLBI Network and the enhanced Multi-Element Remotely Linked Interferometry Network. We find a rarely seen complex radio-emitting nucleus consisting of a collimated jet and an extended non-thermal radio emission region. The diffuse emission region has a size of about 360 pc and a radio luminosity about three times higher than that of the nearby extreme starburst galaxy Arp 220. The powerful nuclear radio activity could result either from a relic jet with a peculiar geometry (nearly along the line of sight) or more likely from diffuse shocks formed naturally by the existing high-speed winds impacting on high-density star-forming regions.

Resolving the Nuclear Radio Emission from M32 with the Very Large Array

Abstract The Local Group dwarf elliptical galaxy M32 hosts one of the nearest and most under-luminous supermassive black holes (SMBHs) ever known, offering a rare opportunity to study the physics of accreting SMBHs at the most quiescent state. Recent Very Large Array (VLA) observations detected a radio source at the nucleus of M32, which was suggested to be the radio counterpart of the SMBH. To further investigate the radio properties of this nuclear source, we have conducted follow-up, high-resolution VLA observations in four epochs between 2015 and 2017, each with dual frequencies. At 6 GHz, the nuclear source is resolved under an angular resolution of ∼0.″4, exhibiting a coreless, slightly lopsided morphology with a detectable extent of ∼2.″5 (∼10 pc). No significant variability can be found among the four epochs. At 15 GHz, no significant emission can be detected within the same region, pointing to a steep intrinsic radio spectrum (with a 3σ upper limit of −1.46 for the spectral index). We discuss possible scenarios for the nature of this nuclear radio source and conclude that a stellar origin, in particular, planetary nebulae, X-ray binaries, supernova remnants, or diffuse ionized gas powered by massive stars, can be ruled out. Instead, the observed radio properties can be explained by synchrotron radiation from a hypothetical wind driven by the weakly accreting SMBH.

Determination the Effects of Hyperthyroidism on Pre-Eclampsia in Women of Balochistan

Thyroid gland is an endocrine gland that reproduces hormones that regulates the body metabolic rate and other body functions. Hyperthyroidism is the dysfunction of thyroid gland which interferes during 2nd and 3rd trimester of pregnancies inducing pre-eclamptic disorder in pregnant women. These disorders may cause deaths as well as morbidity losses in mothers and fetus. These conditions are observed due to imbalance production of T3, T4 and TSH. Hyperthyroidism is highly associated with the onset of pre-eclampsia. Pre-eclampsia is detected by elevated levels of proteinuria as well as systolic and diastolic blood pressures. This study was conceded to discover the influence of hyperthyroidism on pre-eclamptic women of Balochistan. For the purpose, one hundred one (101) pregnant women of 15-50 years of age were selected for this study for comprehensive history, physical and medical examination according to the inclusion and exclusion criteria. Patients of different ethnic groups were examined at Out Patient Department (OPD) in Centre for Nuclear Medicine and Radio therapy (CENAR), Sandeman Provincial Hospital and Bolan Medical Complex hospital (BMC), Quetta. The study focuses on the identification of factors associated with hyperthyroidism and pre-eclampsia and to create awareness regarding this important health issue during pregnancy which may lead to eclamptic seizures during onset of full term labor and are found to be fatal for women and neonate during pregnancy. The current study revealed that out of 101 hyperthyroid patients 61.4% and 20.8% patients belong to Pashtoon and Baloch ethnic groups respectively. It was also found that 44 out of 101 patients lie in age group of 26-35 years. It was observed that highly educated, socioeconomic sound women developed less Pre-eclampsia. Pre-eclampsia was found to be in a significant numbers (33), in hyperthyroid patients, with highest frequency of Pedal edema (36.6%).

Prevalence of neutral gas in centres of merging galaxies−II: nuclear H i and multiwavelength properties

Abstract Using a sample of 38 radio-loud galaxy mergers at z ≤ 0.2, we confirm the high detection rate (∼84 per cent) of H i 21-cm absorption in mergers, which is significantly higher (∼4 times) than in non-mergers. The distributions of the H i column density [$N(\rm{H\,{\small I}}$)] and velocity shift of the absorption with respect to the systemic redshift of the galaxy hosting the radio source in mergers are significantly different from that in non-mergers. We investigate the connection of the nuclear H i gas with various multiwavelength properties of the mergers. While the inferred $N(\rm{H\,{\small I}}$) and gas kinematics do not show strong (i.e. ≥3σ level) correlation with galaxy properties, we find that the incidence and $N(\rm{H\,{\small I}}$) of absorption tend to be slightly higher at smaller projected separations between the galaxy pairs and among the lower stellar mass-radio galaxies. The incidence, $N(\rm{H\,{\small I}}$) and line width of H i absorption increase from the pre-merger to the post-merger stages. The 100 per cent detection rate in post-mergers indicates that the neutral gas in the circumnuclear regions survives the coalescence period and is not yet quenched by the nuclear radio activity.

Nuclear Magnetic Coupled Fast Radio Burst Induced Upregulation of Hsp70 in Regeneration of Human Chondrocytes - A Sham Control Study

Manipulating the cell’s inherent vulnerabilities to induce intrinsic changes and re-engineer diseased tissues to drive regeneration is a domain creating significant therapeutic impact through translational medicine. Articular cartilage injuries are recurrently experienced due to trauma, mechanical stress and age-related deterioration. Prevailing mend methods have failed to yield reliable or lasting results. Lack of suitable models that mimic the cellular and extra cellular matrix properties of hyaline cartilage has been one of the reasons for this deficiency. We investigated and observed, joint tissue obtained during total knee replacement surgeries from 7 discrete patients presenting with osteoarthritis and the commonly associated symptoms of inflammation and pain. We used modulated “Nuclear Magnetic Coupled Fast Radio Burst or simply Fast Radio Bursts”, a new modality that seems to trigger the cellular signaling required by the articular cartilage tissue, to mend and regenerate by upregulation of Heat Shock Protein 70. Fast Radio Bursts are high energy, short electromagnetic bursts, in which both electric and magnetic components of the electromagnetic signals are “circularly” polarized. Fast Radio Bursts are produced when a radio signal is traveling through a powerful instantaneous magnetic field on its path to the target. In this Sham controlled study, up-regulation of Hsp 70 protein, to establish its role in an in vitro model was designed to expose 2-Dimensional and 3-Dimensional cultures to Fast Radio Bursts, and compared to a Sham Control, under identical conditions but without exposing Sham Control culture to fast radio bursts. The 2D and 3D reconstructed cartilage tissues were then assessed in both groups. Experiments were conducted to characterize the 2D and 3D cultures to confirm total collagen, fibrillar collagen and proteoglycans, additionally; immunofluorescence and cell viability assay was performed to identify specific bio markers like Collagen 1, Collagen II, Aggrecan, Cell surface Adhesion factor, Hsp70 and cell viability. It could be established in this study that 2D cultures grown in newly defined media and exposed to Fast Radio Burst signals, when compared to 2D cultures grown as Sham culture showed more chondrocyte specific markers and viable matrix properties. In 3D cultures grown similarly also showed better deep layer properties compared to the 3D cultures grown in sham culture. Thus modulated Fast Radio Bursts exposure could play a significant role in specific protein up/down regulation in tissue regeneration.

Detecting Radio AGN Signatures in Red Geysers

Abstract A new class of quiescent galaxies harboring possible AGN-driven winds has been discovered using spatially resolved optical spectroscopy from the ongoing SDSS-IV MaNGA survey. These galaxies, termed “red geysers,” constitute 5%–10% of the local quiescent population and are characterized by narrow bisymmetric patterns in ionized gas emission features. Cheung et al. argued that these galaxies host large-scale AGN-driven winds that may play a role in suppressing star formation at late times. In this work, we test the hypothesis that AGN activity is ultimately responsible for the red geyser phenomenon. We compare the nuclear radio activity of the red geysers to a matched control sample with similar stellar mass, redshift, rest-frame NUV − r color, axis ratio, and presence of ionized gas. We have used the 1.4 GHz radio continuum data from the VLA FIRST survey to stack the radio flux from the red geyser and control samples. In addition to a three times higher FIRST detection rate, we find that red geysers have a 5σ higher level of average radio flux than control galaxies. After restricting to rest-frame NUV − r color >5 and checking mid-IR WISE photometry, we rule out star formation contamination and conclude that red geysers are associated with more active AGNs. Red geysers and a possibly related class with disturbed Hα emission account for 40% of all radio-detected red galaxies with log (M ⋆/M ⊙) < 11. Our results support a picture in which episodic AGN activity drives large-scale, relatively weak ionized winds that may provide a feedback mechanism for many early-type galaxies.

An Analysis Framework for Understanding the Origin of Nuclear Activity in Low-power Radio Galaxies

Abstract Using large samples containing nearly 2300 active galaxies of low radio luminosity (1.4 GHz luminosity between 2 × 1023 and 3 × 1025 W Hz−1, essentially low-excitation radio galaxies) at z ≲ 0.3, we present a self-contained analysis of the dependence of the nuclear radio activity on both intrinsic and extrinsic properties of galaxies, with the goal of identifying the best predictors of the nuclear radio activity. While confirming the established result that stellar mass must play a key role on the triggering of radio activities, we point out that for the central, most massive galaxies, the radio activity also shows a strong dependence on halo mass, which is not likely due to enhanced interaction rates in denser regions in massive, cluster-scale halos. We thus further investigate the effects of various properties of the intracluster medium (ICM) in massive clusters on the radio activities, employing two standard statistical tools, principle component analysis and logistic regression. It is found that ICM entropy, local cooling time, and pressure are the most effective in predicting the radio activity, pointing to the accretion of gas cooling out of a hot atmosphere to be the likely origin in triggering such activities in galaxies residing in massive dark matter halos. Our analysis framework enables us to logically discern the mechanisms responsible for the radio activity separately for central and satellite galaxies.

Asymptomatic calf vein DVT in high risk surgical patients: a single centre study

Asymptomatic deep vein thrombosis (DVT) of calf veins is a known entity in high risk surgical patients, which can lead to fatal pulmonary embolism. The actual incidence of asymptomatic calf vein DVT in high risk surgical patients is not known in Indian population. We had conducted this study with an aim to determine the incidence of asymptomatic calf vein DVT in spite of providing extended prophylaxis against DVT in high risk patients. Our study was a prospective observational study conducted from Oct 2014 to Mar 2016 in a tertiary care teaching Hospital in Bangalore, in Department of surgery with help of Department of Nuclear medicine and Radio diagnosis. We examined more than 100 patients who were due for some surgical procedure and included 100 patients fell in high risk group with a risk stratification score of ≥ 5. All patients screened for asymptomatic DVT with Duplex ultrasonography scan and 99mTc MAA venography. The patients who were detected to have asymptomatic calf vein DVT were therapeutically managed as cases of DVT. In the study 3 patients detected to have asymptomatic calf vein DVT making the incidence of 3.06%. In our study group we found duration of surgery of more than 60 mins being the most common risk factor followed by malignancy. Our incidence of asymptomatic calf vein DVT was 3.06% in high risk surgical patients. Duplex ultrasonography is a useful, easily available, non invasive and safe diagnostic modality in detecting asymptomatic calf vein DVT.

RelB-siRNA enhanced the radiosensitivity of murine prostate cancer cell line RM-1

To explore the transfecting effects of RelB small interfering RNA (RelB-siRNA) on murine prostate cancer cell line RM-1 sensitivity of radiotherapy. The RM-1 cells were divided into RelB-siRNA vector, empty vector, non-transfection and normal groups. After transfection, the first three groups were irradiated by X ray. Clone formation array method was used to measure the surviving fraction and the relevant parameter values after 0, 2, 4, 6, 8 Gy irradiation. Apoptotic rate was measured via Annexin V/PI flow cytometry after 6 Gy irradiation. The level of RelBmRNA was estimated by real-time polymerase chain reaction (PCR) after 6 Gy irradiation. And the RelB protein of cytoplasm and nucleus was detected by Western blot after 6 Gy irradiation. Clone formation array showed that RelB group at each dose point corresponding to the survival fraction were lower that the empty vector nd non-transfection groups. The D0, Dq and SF2 values of RelB group were 1.68, 0.60, 0.43, lower than those of empty vector group 1.92, 3.08, 0.89 and non-transfection group 1.93, 2.76, 0.84. Annexin V/PI flow cytometry demonstrated that the apoptotic rate of RelB group was 15.27% ± 1.62% and it was significantly higher than the non-transfection group 7.90% ± 1.50% and the empty vector group 8.40% ± 0.69% respectively (P < 0.01) .Real-time PCR indicated that RelB-mRNA amplification of RelB group was 1.18 ± 0.03 and it was significantly lower than the non-transfection group 2.10 ± 0.61 and the empty vector group 1.97 ± 0.66 respectively (P < 0.01) .Western blot suggested that cytoplasmic gray-scale ratio of RelB group was 0.50 ± 0.08 and it was significantly lower than the non-transfection 1.77 ± 0.19 and the empty group 1.52 ± 0.12 respectively (P < 0.01) . And the nuclear gray-scale radio of the RelB group was 0.18 ± 0.03 and it was significantly lower than the non-transfection group 0.61 ± 0.12 and the empty group 0.54 ± 0.13 respectively (P < 0.01) . The RelB protein inhibition rates of cytoplasmic and nuclear RelB-siRNA were 71.8% and 70.4% respectively. RelB-siRNA can effectively inhibit the RelB expression of murine prostate cancer cell line RM-1 and significantly increase its sensitivity to radiotherapy.

On the radio luminosity distribution of active galactic nuclei and the black hole fundamental plane

We have studied the dependence of the nuclear radio (1.4 GHz) luminosity of active galactic nuclei (AGN) on both 2–10 keV X-ray and host-galaxy K-band luminosities. A complete sample of 1268 X-ray-selected AGN (both type 1 and type 2) has been used, which is the largest catalogue of AGN belonging to statistically well-defined samples where radio, X-ray and K-band information exists. At variance with previous studies, radio upper limits have been taken into account statistically using a Bayesian maximum-likelihood fitting method. A good fit is obtained assuming a plane in 3D LR–LX–LK space, namely log LR = ξX log LX + ξK log LK + ξ0, with a ∼1 dex wide (1σ) spread in radio luminosity. As already shown by La Franca, Melini & Fiore, no evidence of bimodality in the radio luminosity distribution was found and therefore any definition of radio-loudness in AGN is arbitrary. Using scaling relations between the black hole (BH) mass and the host galaxy K-band luminosity, we have also derived a new estimate of the BH fundamental plane (in L5 GHz–LX–MBH space). Our analysis shows that previous measures of the BH fundamental plane are biased by ∼0.8 dex in favour of the most luminous radio sources. Therefore, many AGN studies, where the BH fundamental plane is used to investigate how AGN regulate their radiative and mechanical luminosity as a function of the accretion rate, and many AGN/galaxy co-evolution models, where radio feedback is computed using the AGN fundamental plane, should revise their conclusions.

PROPERTIES OF NEARBY STARBURST GALAXIES BASED ON THEIR DIFFUSE GAMMA-RAY EMISSION

The physical relationship between the far-infrared and radio fluxes of star forming galaxies has yet to be definitively determined. The favored interpretation, the "calorimeter model," requires that supernova generated cosmic ray (CR) electrons cool rapidly via synchrotron radiation. However, this cooling should steepen their radio spectra beyond what is observed, and so enhanced ionization losses at low energies from high gas densities are also required. Further, evaluating the minimum energy magnetic field strength with the traditional scaling of the synchrotron flux may underestimate the true value in massive starbursts if their magnetic energy density is comparable to the hydrostatic pressure of their disks. Gamma-ray spectra of starburst galaxies, combined with radio data, provide a less ambiguous estimate of these physical properties in starburst nuclei. While the radio flux is most sensitive to the magnetic field, the GeV gamma-ray spectrum normalization depends primarily on gas density. To this end, spectra above 100 MeV were constructed for two nearby starburst galaxies, NGC 253 and M82, using Fermi data. Their nuclear radio and far-infrared spectra from the literature are compared to new models of the steady-state CR distributions expected from starburst galaxies. Models with high magnetic fields, favoring galaxy calorimetry, are overall better fits to the observations. These solutions also imply relatively high densities and CR ionization rates, consistent with molecular cloud studies.

BROAD-LINE RADIO GALAXIES OBSERVED WITHFERMI-LAT: THE ORIGIN OF THE GeV γ-RAY EMISSION

We report on a detailed investigation of the gamma-ray emission from 18 broad line radio galaxies (BLRGs) based on two years of Fermi Large Area Telescope (LAT) data. We confirm the previously reported detections of 3C 120 and 3C 111 in the GeV photon energy range; a detailed look at the temporal characteristics of the observed gamma-ray emission reveals in addition possible flux variability in both sources. No statistically significant gamma-ray detection of the other BLRGs was however found in the considered dataset. Though the sample size studied is small, what appears to differentiate 3C 111 and 3C 120 from the BLRGs not yet detected in gamma-rays is the particularly strong nuclear radio flux. This finding, together with the indications of the gamma-ray flux variability and a number of other arguments presented, indicate that the GeV emission of BLRGs is most likely dominated by the beamed radiation of relativistic jets observed at intermediate viewing angles. In this paper we also analyzed a comparison sample of high accretion-rate Seyfert 1 galaxies, which can be considered radio-quiet counterparts of BLRGs, and found none were detected in gamma-rays. A simple phenomenological hybrid model applied for the broad-band emission of the discussed radio-loud and radio-quiet type 1 active galaxies suggests that the relative contribution of the nuclear jets to the accreting matter is > 1 percent on average for BLRGs, whilst <0.1 percent for Seyfert 1 galaxies.

The core-collapse supernova rate in Arp 299 revisited

We present a study of the CCSN rate in nuclei A and B1 of the luminous infrared galaxy Arp299, based on 11 years of Very Large Array monitoring of their radio emission at 8.4 GHz. Significant variations in the nuclear radio flux density can be used to identify the CCSN activity in the absence of high-resolution very long baseline interferometry observations. In the case of the B1-nucleus, the small variations in its measured diffuse radio emission are below the fluxes expected from radio supernovae, thus making it well-suited to detect RSNe through flux density variability. In fact, we find strong evidence for at least three RSNe this way, which results in a lower limit for the CCSN rate of 0.28 +/- 0.16 per year. In the A-nucleus, we did not detect any significant variability and found a SN detection threshold luminosity which allows only the detection of the most luminous RSNe known. Our method is basically blind to normal CCSN explosions occurring within the A-nucleus, which result in too small variations in the nuclear flux density, remaining diluted by the strong diffuse emission of the nucleus itself. Additionally, we have attempted to find near-infrared counterparts for the earlier reported RSNe in the Arp299 nucleus A, by comparing NIR adaptive optics images from the Gemini-N telescope with contemporaneous observations from the European VLBI Network. However, we were not able to detect NIR counterparts for the reported radio SNe within the innermost regions of nucleus A. While our NIR observations were sensitive to typical CCSNe at 300 mas from the centre of the nucleus A, suffering from extinction up to A_v~15 mag, they were not sensitive to such highly obscured SNe within the innermost nuclear regions where most of the EVN sources were detected. (abridged)

Multi-Wavelength Studies on H2O Maser Host Galaxies

H2O maser emissions have been found in external galaxies for more than 30 years. Main sciences associated with extragalactic H2O masers can be summarized roughly into three parts: maser emission itself, AGN sciences and cosmology exploration. Our work in this field focusses on two projects: X-ray data analysis of individual maser source using X-ray penetrability to explore maser host obscured AGN; multi-wavelength statistical properties of the whole published H2O maser sample. Here their nuclear radio properties were investigated in detail, based on their 6-cm and 20-cm radio observation data. Comparing the radio properties between maser-detected sources and non-detected sources at similar distance scale, we find that: (1) maser host galaxies tend to have higher nuclear radio luminosity; (2) the spectral index of both samples is comparable (∼0.6), within the error ranges. In addition, for AGN-maser sources, the isotropic maser luminosity tends to increase with rising radio luminosity. Thus we propose the nuclear radio luminosity as one good indicator for searching AGN-masers in the future.

SEYFERT GALAXIES: NUCLEAR RADIO STRUCTURE AND UNIFICATION

A radio study of a carefully selected sample of 20 Seyfert galaxies that are matched in orientation-independent parameters, which are measures of intrinsic active galactic nuclei (AGN) power and host galaxy properties is presented to test the predictions of the unified scheme hypothesis. Our sample sources have core flux densities greater than 8 mJy at 5 GHz on arcsec-scales due to the feasibility requirements. These simultaneous pc-scale and kpc-scale radio observations reveal (i) that Seyfert 1 and Seyfert 2 galaxies have equal tendency to show compact radio structures on mas-scales, (ii) the distributions of pc-scale and kpc-scale radio luminosities are similar for both Seyfert 1 and Seyfert 2 galaxies, (iii) no evidence for relativistic beaming in Seyfert galaxies, (iv) similar distributions of source spectral indices in spite of the fact that Seyferts show nuclear radio flux density variations, and (v) the distributions of projected linear size for Seyfert 1 and Seyfert 2 galaxies are not significantly different as would be expected in the unified scheme. The latter could be mainly due to a relatively large spread in the intrinsic sizes. We also find that a starburst alone cannot power these radio sources. Finally, an analysis of the kpc-scale radio properties of the CfA Seyfert galaxy sample shows results consistent with the predictions of the unified scheme.