Radio Core Dominance Research Articles

Statistical Tests of the Relativistic Beaming Indicators of jetted AGNs and Implication for the Revised Blazar Sequence

The latest detection by the Fermi Large Area Telescope (Fermi-LAT) of strong relativistic jets of very high-energy (VHE, above 100 GeV) from the Narrow-Line Seyfert 1 Galaxies (NLS1s) has opened a new unified scheme of active galactic nuclei (AGN) in which jetted Seyfert galaxies are viewed as counterparts to a subclass of AGNs. In this paper, we report a systematic investigation of the revised blazar sequence using the γ-ray Doppler factor () and the radio core-dominance parameter (R) of AGN samples of NLS1s and blazar subtypes of flat-spectrum radio quasars (FSRQs) and BL Lac objects (BLs). Furthermore, we explore the γ-ray properties of NLS1s and blazar subtypes in the context of the blazar unification scheme at different scales. The main results are as follows: (a) The average values of R and γ-ray luminosity () of our sample agree with the sequence BLs – FSRQs – NLS1s and provide quantitative explanations for the observed relativistic beaming effects in these objects. (b) Through a parameter t-test and non-parametric K-S test with chance probability p <10-3, we find that the distributions of R and Lγ for NLS1s and the blazar subtypes are not significantly different. (c) There is a regular positive trend (r > +0.79) in the variation of Lγ – data from BLs to NLS1s through FSRQs which is consistent with the prediction of the revised blazar sequence. These results imply that NLS1s could fit very well into the conventional blazar sequence.

Determining the ratio of the jet to the unbeamed luminosities for γ-ray blazars

ABSTRACT The spectacular observational phenomena lying in blazars can be well explained and described by the relativistic beaming effect that the emission in the jet is highly boosted along the line of sight to observers. Aiming to reveal the intrinsic emission core dominance in γ-ray loud blazars, we collect a large sample including 226 blazars with available superluminal motion data and radio core-dominance parameters at 5 GHz, and calculate a crucial parameter, R⊥, defined as the ratio of the luminosity in the jet to the unbeamed luminosity when the viewing angle comes up to 90°. R⊥ is a better parameter than the well-known core-dominance parameter, R, to reveal more intrinsic physical properties behind the prominent observational characteristics within blazars. We primarily ascertain the updated median value of R⊥ = 0.032 at 5 GHz, illustrating around 97 per cent of the total radio emission are dominated by the jets in γ-ray loud blazars. We also make further discussion on the physical difference in BL Lacertae objects and flat-spectrum radio quasars.

Two-component TeV Emissions for Blazars

For blazars, its radio emissions are composed of two components. In the high energy bands, Tera-electronvolts (TeV; 1012electronvolts) emissions were detected from some blazars. Does the TeV emission also consist of two components? To investigate the TeV emission component, we compiled a sample of 51 TeV blazars with available radio core dominance parameters and applied a two-component (the beamed and the unbeamed) model to study the composition of blazar TeV emission. We obtained the core-dominance parameter at the TeV band through applying a relativistic beaming model, and found that the average TeV core-dominance parameter is for 46 BL Lacs, and that is for 5 FSRQs, which shows an indication that the core dominance parameter in BL Lacs is smaller than that in FSRQs. For the three subclasses of BL Lacs—high synchrotron peaked BL Lacs(HBLs), intermediate synchrotron peaked BL Lacs(IBLs) and low synchrotron peaked(LBLs), is smaller than and . Our results suggest that the blazar TeV emission from the core is thousands times stronger than from the extended region and the TeV emission is more core-dominated for the lower synchrotron peaked sources. In addition, a significant correlation between the TeV core-dominance parameter () and the radio one () , is obtained suggesting that the TeV emission is beamed and the TeV core-dominance parameter is an indicator of beaming effect at the TeV bands, and that the TeV emission has stronger beaming effect than the radio emission.

Fraction of broad absorption line quasars in different radio morphologies

ABSTRACT In this study, we investigated the orientation model of Broad Absorption Line (BAL) quasars using a sample of sources that are common in Sloan Digital Sky Survey (SDSS) Data Release (DR)-16 quasar catalogue and Very Large Array (VLA)-Faint Images of the Radio Sky at Twenty Centimeters (FIRST) survey. Using the radio cut-out images from the FIRST survey, we first designed a deep-learning model using convolutional neural networks (CNN) to classify the quasar radio morphologies into the core-only, young jet, single lobe, or triples. These radio morphologies are further sub-classified into core-dominated and lobe-dominated sources. The CNN models can classify the sources with a high precision of >98 ${{\ \rm per\ cent}}$ for all the morphological sub-classes. The average BAL fraction in the resolved core, core-dominated, and lobe-dominated quasars are consistent with the BAL fraction inferred from radio and infrared surveys. We also present the distribution of BAL quasars as a function of quasar orientation by using the radio core-dominance as an orientation indicator. A similar analysis is performed for HiBALs, LoBALs, and FeLoBALs. All the radio morphological sub-classes and BAL sub-classes show an increase in BAL fraction at high orientation angles of the jets with respect to the line of sight. Our analysis suggests that BAL quasars are more likely to be found in viewing angles close to the equatorial plane of the quasar. However, a pure orientation model is inadequate, and a combination of orientation and evolution is probably the best way to explain the complete BAL phenomena.

Orientation and Accretion in a Representative Sample of Active Galactic Nuclei

Abstract We highlight a representative sample of active galactic nuclei selected independent of orientation. The defining characteristic of the selection is sophisticated matching between the 0.1 < z < 0.6 Sloan Digital Sky Survey quasars from the Seventh Data Release to the Westerbork Northern Sky Survey at 325 MHz and the subsequent application of a spatially integrated radio spectral luminosity density cut. The resulting sample is complete down to the limiting luminosity and unbiased by orientation. Compared to orientation samples in the literature this approach yields less bias with redshift, relatively more lobe-dominated sources including those with radio lobes and no visible core, and a distribution of radio core dominance that is consistent with expectations from a uniform distribution of inclinations with solid angle. We measure properties of the optical spectra, and use the sample to investigate the orientation dependence of the velocity width of the broad Hβ emission line. We recover the known orientation dependence, but the sharp envelope of previous studies where only edge-on sources display the broadest lines, is absent. Scatter in this diagram is not attributable solely to black hole mass, Eddington ratio, or contamination in the sample from compact steep-spectrum sources. A physical framework for quasar beaming and a disk-like broad-line region can describe the representative sample when it is expanded to include additional parameters, in particular jet properties and the broad-line region velocity field. These points serve to illustrate the critical role of sample selection in the interpretation of observable properties as indicators of physical parameters of quasar central engines.

Radio core-dominance of Fermi-blazars: implication for blazar unification

...The 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 greater than 0.60 between core-dominance parameter and extended luminosity 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 Core-dominance parameter-extended luminosity plane. Nevertheless, little or no correlation between Core-dominance parameter and core luminosity or between Core dominance parameter and gamma-ray luminosity r, less than 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 the largest scales.

Investigating Orientation Effects Considering Angular Resolution for a Sample of Radio-loud Quasars Using VLA Observations

Abstract Radio core dominance measurements, an indicator of jet orientation, sometimes rely on core flux density measurements from large-area surveys like Faint Images of the Radio Sky at Twenty cm (FIRST) that have an angular resolution of only 5″. Such low-resolution surveys often fail to resolve cores from the extended emission, resulting in an erroneous measurement. We focus on investigating this resolution effect for a sample of 119 radio-loud quasars. We obtained continuum observations from NSF’s Karl G. Jansky Very Large Array (VLA) at 10 GHz in A configuration with a 0.″2 resolution. Our measurements show that at FIRST spatial resolution, core flux measurements are indeed systematically high even after considering the core variability. For a handful of quasars, 10 GHz images reveal extended features, whereas the FIRST image shows a point source. We found that the resolution effect is more prominent for quasars with smaller angular sizes. We further computed two radio core dominance parameters R and R 5100 for use in statistical orientation investigations with this sample. We also present the spectral energy distributions between 74 MHz and 1.4 GHz, which we used to measure the spectral index of the extended emission of these quasars. Our results empirically confirm that determination of radio core dominance requires high spatial resolution data. We highlight the practical issues associated with the choice of frequency and resolution in the measurement of core and extended flux densities.

Beamed and Unbeamed Emission of γ-Ray Blazars

A two-component model of radio emission has been used to explain some radio observational properties of Active Galactic Nuclei (AGNs) and, in particular, of blazars. In this work, we extend the two-component idea to the γ-ray emission and assume that the total γ-ray output of blazars consists of relativistically beamed and unbeamed components. The basic idea leverages the correlation between the radio core-dominance parameter and the γ-ray beaming factor. To do so, we evaluate this correlation for a large sample of 584 blazars taken from the fourth source catalog of the Fermi Large Area Telescope (Fermi-LAT) and correlated their γ-ray core-dominance parameters with radio core-dominance parameters. The γ-ray beaming factor is then used to estimate the beamed and unbeamed components. Our analysis confirms that the γ-ray emission in blazars is mainly from the beamed component.

The relationship between the radio core-dominance parameter and spectral index in different classes of extragalactic radio sources (III)

Active galactic nuclei (AGNs) can be divided into two major classes, namely radio-loud and radio-quiet AGNs. A small subset of the radio-loud AGNs is called blazars, which are believed to be unified with Fanaroff-Riley type I and type II (FRI&II) radio galaxies. Following our previous work, we present a latest sample of 966 sources with measured radio flux densities of the core and extended components. The sample includes 83 BL Lacs, 473 flat spectrum radio quasars, 101 Seyferts, 245 galaxies, 52 FRIs&IIs and 12 unidentified sources. We then calculate the radio core-dominance parameters and spectral indices and study their relationship. Our analysis shows that the core-dominance parameters and spectral indices are quite different for different types of sources. We also confirm that the correlation between core-dominance parameter and radio spectral index extends over all the sources in a large sample presented.

Radio core dominance of Fermi/LAT-detected AGNs

We present a sample of 4388 AGNs with available radio core-dominance parameters—defined as the ratio of the core flux densities to the extended ones, R = Score/Sext.—which includes 630 Fermi-detected AGNs from the fourth source catalog (4FGL) of the Fermi Large Area Telescope (Fermi/LAT); the rest are non-Fermi-detected AGNs. In our sample, 584 blazars are Fermi-detected and 1310 are not. The sample also contains other subclasses, such as Seyferts, Fanaroff-Riley I/II galaxies, and normal galaxies. We investigate various properties of the Fermi-detected and non-Fermi-detected AGNs by using core-dominance parameters, capitalizing on a previous study which showed that R is a good indicator of beaming. We then calculate radio spectral indices for the whole sample, and adopt γ-ray-photon indices for the Fermi AGNs from the 4FGL catalog to discuss the properties of different subclasses. We obtain a relation between the core-dominance parameters and the radio spectral indices for both Fermi and non-Fermi sources, assuming a two-component model in the radio band. Our previous study ruled out the assumption that the core-dominance parameters and radio spectral indices are quite different for different AGN subclasses. This holds not only for Fermi sources but also for non-Fermi sources. In particular, R is, on average, greater for the former AGNs than for the latter. In this study, we enlarge our sample with available values of R to 4388 AGNs, and the obtained conclusions are consistent with our previous study. We assume that the same two-component model holds for the γ-ray band as for the radio band, and therefore, adopt the same relation between the core-dominance parameters and the γ-ray-photon indices for Fermi AGNs. Our fitting results indicate that the γ-ray emissions of Fermi blazars originate mainly from the jet, and therefore, we conclude that the Fermi blazars are beamed.

The estimation of γ-ray Doppler factor forFermi/LAT-detected blazars

AbstractBlazars are a subclass of active galactic nuclei with extreme observation properties, which is caused by the beaming effect, expressed by a Doppler factor ($\delta$), in a relativistic jet. Doppler factor is an important parameter in the blazars paradigm to indicate all of the observation properties, and many methods were proposed to estimate its value. In this paper, we present a method following Mattox et al. to calculate the lower limit on$\gamma$-ray Doppler factor ($\delta_{\gamma}$) for 809 selectedFermi/LAT-detected$\gamma$-ray blazars by adopting the available$\gamma$-ray and X-ray data. Our sample included 342 flat-spectrum radio quasars (FSRQs) and 467 BL Lac objects (BL Lacs), out of which 507 sources are compiled with available radio core-dominance parameter (R) from our previous study. Our calculation shows that the average values of the lower limit on$\delta_{\gamma}$for FSRQs and BL Lacs are$\left\langle\delta_{\gamma}|_{\textrm{FSRQ}}\right\rangle = 6.87 \pm 4.07$and$\left\langle\delta_{\gamma}|_{\textrm{BL\ Lac}}\right\rangle=4.31 \pm 2.97$, respectively. We compare and discuss our results with those from the literature. We found that the derived lower limit on$\delta_{\gamma}$for some sources is higher than that from the radio estimation, which could be possibly explained by the jet bending within those blazars. Our results also suggest that the$\gamma$-ray and radio regions perhaps share the same relativistic effects. The$\gamma$-ray Doppler factor has been found to be correlated with both the$\gamma$-ray luminosity and core-dominance parameter, implying that the jet is possibly continuous in the$\gamma$-ray bands, andRis perhaps an indicator for a beaming effect.

The relationship between the radio core-dominance parameter and spectral index in different classes of extragalactic radio sources (II)

Active galactic nuclei (AGNs) can be divided into two major classes, namely radio-loud and radio-quiet AGNs. A small subset of the radio-loud AGNs is called blazars, which are believed to be unified with Fanaroff-Riley type I/II (FRI/II) radio galaxies. Following our previous work (Fan et al.), we present a sample of 2400 sources with measured radio flux densities of the core and extended components. The sample contains 250 BL Lacs, 520 quasars, 175 Seyferts, 1178 galaxies, 153 FRI or FRII galaxies and 104 unidentified sources. We then calculate the radio core-dominance parameters and spectral indices, and study their relationship. Our analysis shows that the core-dominance parameters and spectral indices are quite different for different types of sources. We also confirm that the correlation between core-dominance parameter and spectral index exists for a large sample presented in this work.

A ROBUST DERIVATION OF THE TIGHT RELATIONSHIP OF RADIO CORE DOMINANCE TO INCLINATION ANGLE IN HIGH REDSHIFT 3CRR SOURCES

ABSTRACT It is believed that, in radio-loud active galactic nuclei (AGNs), the core radio flux density can be normalized to the flux density of the extended lobe emission to infer the orientation of a radio source. However, very little is known about the reliability and precision of this method, and we are unaware of any robust conversion recipe to infer the inclination from the core dominance. Investigating whether or not the radio core dominance parameter R separates the quasars from the radio galaxies in the 1 3CRR catalog, we found excellent agreement of R with optical type, infrared flux ratios, and optical polarization. This indicates that probably both R and optical classification are very good orientation indicators, and the unified model is strongly predictive for these objects. The relative number densities indicate half-opening angles close to 60°, as expected from large surveys. The separations of optical types according to radio core dominance as well as near-infrared/MIR ratios, which are essentially perfect, mean that there can be only a small dispersion of torus half-opening angles. Also, even though torus dust is thought to be clumpy, there is an almost zero probability to see a type-1 source at high inclination. Finally, using only the Copernican Principle, i.e., the assumption that solid angle is filled uniformly with source axis orientations, we estimated a semi-empirical relation between core dominance and AGN inclination. This makes it possible to use R to infer the inclination of a source to an accuracy of ∼10° or less, at least for this type of object.

Erratum to: Radio core dominance of Fermi blazars

Erratum to: Radio core dominance of Fermi blazars

The column density distribution of hard X-ray radio galaxies

In order to investigate the role of absorption in AGN with jets, we have studied the column density distribution of a hard X-ray selected sample of radio galaxies, derived from the INTEGRAL/IBIS and Swift/BAT AGN catalogues (~7-10% of the total AGN population). The 64 radio galaxies have a typical FRII radio morphology and are characterized by high 20-100 keV luminosities (from 10^42 to 10^46 erg/s) and high Eddington ratios (Log L_{Bol}/L_{Edd} typically larger than ~0.01). The observed fraction of absorbed AGN (N_{H} > 10^{22} cm^{-2}) is around 40% among the total sample, and ~75% among type 2 AGN. The majority of obscured AGN are narrow line objects, while unobscured AGN are broad line objects, obeying to the zeroth-order predictions of unified models. A significant anti-correlation between the radio core dominance parameter and the X-ray column density is found. The observed fraction of Compton thick AGN is ~2-3%, in comparison with the 5-7% found in radio-quiet hard X-ray selected AGN. We have estimated the absorption and Compton thick fractions in a hard X-ray sample containing both radio galaxies and non-radio galaxies and therefore affected by the same selection biases. No statistical significant difference was found in the absorption properties of radio galaxies and non radio galaxies sample. In particular, the Compton thick objects are likely missing in both samples and the fraction of obscured radio galaxies appears to decrease with luminosity as observed in hard X-ray non-radio galaxies.

Orientation and quasar black hole mass estimation

We have constructed a sample of 386 radio-loud quasars with z < 0.75 from the Sloan Digital Sky Survey in order to investigate orientation effects on black hole mass estimates. Orientation is estimated using radio core dominance measurements based on FIRST survey maps. Black hole masses are estimated from virial-based scaling relationships using H-beta, and compared to the stellar velocity dispersion (sigma_*), predicted using the Full Width at Half Maximum (FWHM) of [O III] 5007, which tracks mass via the M-sigma_* relation. We find that the FWHM of Hbeta correlates significantly with radio core dominance and biases black hole mass determinations that use it, but that this is not the case for sigma_* based on [O III] 5007. The ratio of black hole masses predicted using orientation-biased and unbiased estimates, which can be determined for radio-quiet as well as radio-loud quasars, is significantly correlated with radio core dominance. Although there is significant scatter, this mass ratio calculated in this way may in fact serve as an orientation estimator. We additionally note the existence of a small population radio core-dominated quasars with extremely broad H-beta emission lines that we hypothesise may represent recent black hole mergers.

Comparing different indicators of quasar orientation

Radio core dominance, the rest-frame ratio of core to lobe luminosity, has been widely used as a measure of Doppler boosting of a quasar's radio jets and hence of the inclination of the central engine's spin axis to the line of sight. However, the use of the radio lobe luminosity in the denominator (essentially to try and factor out the intrinsic power of the central engine) has been criticized and other proxies for the intrinsic engine power have been proposed. These include the optical continuum luminosity, and the luminosity of the narrow-line region. Each is plausible, but so far none has been shown to be clearly better than the others. In this paper we evaluate four different measures of core dominance using a new sample of 126 radio loud quasars, carefully selected to be as free as possible of orientation bias, together with high quality VLA images and optical spectra from the SDSS. We find that normalizing the radio core luminosity by the optical continuum luminosity yields a demonstrably superior orientation indicator. In addition, by comparing the equivalent widths of broad emission lines in our orientation-unbiased sample to those of sources in the MOJAVE program, we show that the beamed optical synchrotron emission from the jets is not a significant component of the optical continuum for the sources in our sample. We also discuss future applications of these results.

The behaviour of quasar C iv emission-line properties with orientation

With a quasar sample designed for studying orientation effects, we investigate the orientation dependence of characteristics of the C IV 1549 broad emission line in approximately 50 Type 1 quasars with z=0.1-1.4. Orientation is measured for the sample via radio core dominance. In our analysis we include measurements of the continuum luminosity and the optical-to-X-ray spectral slope, spectral properties commonly included in the suite known as "Eigenvector 1", and the full-width at half maximum, full-width at one-quarter-maximum, shape, blueshift, and equivalent width of the C IV broad emission line. We also investigate a new prescription that we recently developed for predicting the velocity line width of the H-beta broad emission line based on the velocity line width of the C IV line and the ratio of continuum subtracted peak fluxes of Si IV + O IV] at 1400 A to C IV. In addition to a correlation analysis of the ultraviolet spectral properties and radio core dominance, we provide composite spectra of edge-on and face-on sources for this sample. In particular, we highlight the orientation dependence of the velocity line width predicted for H-beta. We find that this predicted line width depends on orientation in a manner similar to the true velocity line width of H-beta, where no such dependence is observed for C IV. This is an indication that orientation information concerning the line emitting regions can be extracted from ultraviolet spectra. [abridged]

An optical spectroscopic survey of the 3CR sample of radio galaxies withz&lt; 0.3

We explore the implications of our optical spectroscopic survey of 3CR radio sources with z<0.3 for the unified model (UM) for radio-loud AGN, focusing on objects with a FRII radio morphology. The sample contains 33 high ionization galaxies (HIGs) and 18 broad line objects (BLOs). According to the UM, HIGs, the narrow line sources, are the nuclearly obscured counterparts of BLOs. The fraction of HIGs indicates a covering factor of the circumnuclear matter of 65% that corresponds, adopting a torus geometry, to an opening angle of 50+/-5 degree. No dependence on redshift and luminosity on the torus opening angle emerges. We also consider the implications for a 'clumpy' torus. The distributions of radio luminosity of HIGs and BLOs are not statistically distinguishable, as expected from the UM. Conversely, BLOs have a radio core dominance, R, more than ten times larger than HIGs, as expected in case of jet Doppler boosting. Modeling the R distributions leads to an estimate of the jet bulk Lorentz factor of Gamma ~3-5. The test of the UM based on the radio source size is not conclusive due to the limited number of objects. Studying the emission line ([OIII], [OII]and [OI]) properties of HEGs and BLOs, we find evidences of a narrow line region (NLR) density stratification and its partial obscuration from the torus. In conclusion, the radio and NLR properties of HIGs and BLOs are consistent with the UM predictions. We also explored the radio properties of 21 3CR FRII low-ionization galaxies (LIGs) at z<0.3. We find that they cannot be part of the model that unifies HIGs and BLOs, but they are instead intrinsically different source, still reproduced by a randomly oriented population.

The orientation dependence of quasar spectral energy distributions

We investigate the orientation dependence of the spectral energy distributions in a sample of radio-loud quasars. Selected specifically to study orientation issues, the sample contains 52 sources with redshifts in the range 0.16<z<1.4 and measurements of radio core dominance, a radio orientation indicator. Measured properties include monochromatic luminosities at a range of wavelengths between the infrared and X-rays, integrated infrared luminosity, spectral slopes, and the covering fraction of the obscuring circumnuclear dust. We estimate dust covering fraction assuming that the accretion disk emits anisotropically and discuss the shortcomings and technical difficulties of this calculation. Luminosities are found to depend on orientation, with face-on sources factors of a 2-3 brighter than more edge-on sources, depending on wavelength. The degree of anisotropy varies very little with wavelength such that the overall shape of the spectral energy distribution does not vary significantly with orientation. In the infrared, we do not observe a decrease in anisotropy with increasing wavelength. The spectral slopes and estimates of covering fraction are not significantly orientation dependent. We construct composite spectral energy distributions as a function of radio core dominance and find that these illustrate the results determined from the measured properties.