Radio-intermediate Quasars Research Articles

A cosmological distance measure using radio-loud quasars

ABSTRACT We use the X-ray luminosity relation of radio-loud quasars (RLQs) to measure these luminosity distances as well as estimate cosmological parameters. We adopt four parametric models of X-ray luminosity to test luminosity correlation for RLQs and radio-intermediate quasars (RIQs) and give these cosmological distances. By Bayesian information criterion (BIC), the data suggest that the luminosity relation ${L_X} \propto L_{\rm UV}^{{\gamma _{\rm uv}}}L_{\rm Radio}^{\gamma _{\rm radio}^{\prime }}$ for RLQs has a better goodness of fit, relative to other models, which can be interpreted as this relation being preferred for RLQs. Meanwhile, we compare the results from flat-spectrum radio-loud quasars (FSRLQs) and steep-spectrum radio-loud quasars (SSRLQs), which indicate that their luminosity correlations are not exactly the same. We also consider dividing the RLQ sample into various redshift bins, which can be used to check if the X-ray luminosity relation depends on the redshift. Finally, we apply a combination of RLQs and SN Ia Pantheon to verify the nature of dark energy concerning whether or not its density deviates from the constant, and give the statistical results.

Outflows in the radio-intermediate quasar III Zw 2: a polarization study with the EVLA and uGMRT

ABSTRACT We present results from a polarization study of the radio-intermediate quasar, III Zw 2, at a redshift of 0.089, with the upgraded Giant Metrewave Radio Telescope (uGMRT) at 685 MHz and the Karl G. Jansky Very Large Array (VLA) at 5 and 34 GHz. We detect a kpc-scale outflow, exhibiting transverse magnetic (B-) fields. The curved jet terminates in a bow-shock-like radio structure with inferred B-fields aligned with the lobe edges. We suggest that the radio outflow in III Zw 2 is a combination of a collimated jet along with a wind-like component. This ‘wind’ component could be a magnetized accretion disc wind or the outer layers of a broadened jet or a combination of both. The current data cannot differentiate between these possibilities. We also detect kpc-scale lobe emission that is misaligned with the primary lobes in the uGMRT images. The spectral indices and the electron lifetimes in the misaligned lobe are similar to the primary lobe, suggesting that the misaligned lobe is not a relic. We propose that changing spectral states of the accretion disc, and the subsequent intermittent behaviour of the outflow, along with the close interplay between the jet and ‘wind’ could explain the radio-intermediate nature of III Zw 2. Our study shows that radio-intermediate quasars are promising sources for understanding the role of jets and winds in galaxy evolution and demonstrates the power of radio polarization studies towards achieving this.

DISCOVERY OF γ-RAY EMISSION FROM THE RADIO-INTERMEDIATE QUASAR III ZW 2: VIOLENT JET ACTIVITY WITH INTRADAY γ-RAY VARIABILITY

ABSTRACT III Zw 2 is the prototype of radio-intermediate quasars. Although there is the evidence of possessing strong jet, significant γ-ray emission has not been reported before. In this work, we carry out a detailed analysis of the latest Fermi-LAT Pass 8 data. No significant γ-ray signal has been detected in the time-averaged 7-year Fermi-LAT data of III Zw 2; however, we have identified two distinct γ-ray flares with isotropic luminosities of ∼1045 erg s−1. Multiwavelength data analysis (also including the optical photometric observations from Yunnan Observatories) are presented and the main finding is simultaneous optical and γ-ray flares of III Zw 2 appearing in 2009 November. Violent γ-ray variability with a doubling timescale of 2.5 hr was detected in another γ-ray flare in May 2010, for which the 3-hr γ-ray peak flux is ∼250 times of the average flux in 7 years. Rather similar behaviors are observed in blazars and the blazar model can reasonably reproduce the spectral energy distribution of III Zw 2 in a wide energy range, strongly suggesting that its central engine resembles that of blazars. In view of its core, which shares radio similarities with young radio sources, together with weak extended radio lobe emission, we suggest that III Zw 2 harbors a recurrent activity core and thus serves as a valuable target for investigating the fueling and triggering of the activity in radio-loud active galactic nuclei.

Improved characterization of intranight optical variability of prominent AGN classes

The incidence of intra-night optical variability (INOV) is known to to differ significantly among different classes of powerful active galactic nuclei (AGN). A number of statistical methods have been employed in the literature for testing the presence of INOV in the light curves, sometimes leading to discordant results. In this paper we compare the INOV characteristics of six prominent classes of AGN, as evaluated using three commonly used statistical tests, namely the $\chi^2-$test, the modified $C-$test and the $F-$test, which has recently begun to gain popularity. The AGN classes considered are: radio-quiet quasars (RQQs), radio-intermediate quasars (RIQs), lobe-dominated quasars (LDQs), low optical polarization core-dominated quasars (LPCDQs), high optical polarization core-dominated quasars (HPCDQs), and TeV blazars. Our analysis is based on a large body of AGN monitoring data, involving 262 sessions of intra-night monitoring of a total 77 AGN, using 1-2 metre class optical telescopes located in India. In order to compare the usefulness of the statistical tests, we have also subjected them to a `sanity check' by comparing the number of false positives yielded by each test with the corresponding statistical prediction. The present analysis is intended to serve as a benchmark for future INOV studies of AGN of different classes.

The environment of weak emission-line quasars

The nature of weak emission-line quasars (WLQs) is probed by comparing the Baldwin effect (BEff) in WLQs and normal quasars (QSOs). We selected 81 high-redshift (z>2.2) and 2 intermediate-redshift (z=1.66 and 1.89) WLQs. Their rest-frame equivalent widths (EWs) of the C IV emission-line and their Eddington ratio were obtained from the Sloan Digital Sky Survey Data Release 7 (SDSS DR7) Quasar Catalogue or from Diamond-Stanic et al. We compare the parameters of WLQs with these of 81 normal quasars from Bright Quasar Survey (BQS) and 155 radio-quiet and radio-intermediate quasars detected by SDSS and Chandra. The influence of the Eddington ratio, Lbol/Ledd, and the X-ray to optical luminosity ratio,alpha_ox, on the BEff is analysed. We find that WLQs follow a different relationship on the EW(CIV)-Lbol/Ledd plane than normal quasars. This relationship disagrees with the super-Eddington hypothesis. The weakness/absence of emission-lines in WLQs does not seem to be caused by their extremely soft ionizing continuum but by low covering factor (Omega) of their broad line region (BLR). Comparing emission-line intensities indicates that the ratios of high-ionization line and low-ionization line regions (i.e. Omega_(HIL)/Omega_(LIL)) are lower in WLQs than in normal QSOs. The covering factor of the regions producing C IV and Lyalpha emission-lines are similar in both WLQs and QSOs.

Optical variability of radio-intermediate quasars

We report the results of our intensive intranight optical monitoring of 8 `radio-intermediate quasars' (RIQs) having flat or inverted radio spectra. The monitoring was carried out in {\it R-} band on 25 nights during 2005-09. An intranight optical variability (INOV) detection threshold of $\sim$ 1--2% was achieved for the densely sampled differential light curves (DLCs). These observations amount to a large increase over those reported hitherto for this rare and sparsely studied class of quasars which can, however, play an important role in understanding the link between the dominant varieties of powerful AGN, namely the radio-quiet quasars (RQQs), radio-loud quasars (RLQs) and blazars. Despite the probable presence of relativistically boosted nuclear jets, clear evidence for INOV in our extensive observations was detected only on one night. These results demonstrate that as a class, RIQs are much less extreme in nuclear activity compared to blazars. The availability in the literature of INOV data for another 2 RIQs conforming to our selection criteria allowed us to enlarge the sample to 10 RIQs (monitored on a total of 42 nights for a minimum duration of $\sim 4$ hours per night). The absence of large amplitude INOV $(\psi > 3%)$ persists in this enlarged sample. This extensive database has enabled us to arrive at the first estimate for the INOV Duty Cycle (DC) of RIQs. The DC is found to be small ($\sim$ 9%). The corresponding value is known to be $\sim 60%$ for BL Lacs and $\approx 15%$ for RLQs and RQQs. On longer-term, the RIQs are found to be fairly variable with typical amplitudes of $\approx$ 0.1-mag. The light curves of these RIQs are briefly discussed in the context of a theoretical framework proposed earlier for linking this rare kind of quasars to the much better studied dominant classes of quasars.

Mid‐Infrared Spectroscopy of High‐Redshift Obscured Quasars

We present mid-infrared observations of 18 sources from a sample of 21 z~2 radio-intermediate obscured quasars. The mid-infrared spectra of the sources are continuum dominated, and 12 sources show deep silicate absorption with tau_9.7~1-2. Combining mid-infrared and optical spectra, we achieve 86% spectroscopic completeness which allows us to confirm that most (63 +14 -22 %) z~2 radio-intermediate quasars are obscured. The new spectra also prove that many high-redshift type-2 quasars do not show any rest-frame ultraviolet emission lines. From the 18 individual mid-infrared spectra, we classify most of the sources into three subsamples: those with hints of the 7.7 and 6.2 micron polyaromatic hydrocarbons (3/18 sources show PAHs, subsample A), those with an excess of emission around 8 micron but no hint of the 6.2 micron PAH (7/18 cases, subsample B) and pure-continuum sources with no visible excess (4/18 sources, subsample C). The remaining 4/18 sources have spectra that are featureless or too noisy for any features to be visible. In subsample A, averaging the spectra leads to a statistical detection of both 6.2 and 7.7 micron PAHs over the continuum, with the strength of the 7.7 micron PAH comparable to that of submillimetre-selected galaxies (SMGs) at similar redshifts. These sources are in a phase of coeval growth of a supermassive black hole and a host galaxy.

Optical Microvariability in Radio-quiet Quasars

We report the results of a study of optical microvariability in radio-quiet and radio-intermediate quasars. Observations were obtained on a total of seven objects: five radio-quiet quasars and two radio-intermediate quasars. No microvariability was detected in either the radio-quiet or radio-intermediate objects in our sample, despite intensive monitoring for several consecutive nights. In one object, PG 1257+346, evidence for interday variability was detected. We examined a sample of 117 radio-quiet objects found in the literature that have been studied for microvariability. This sample is discussed in terms of classification, redshift distribution, R (the ratio of the radio [5 GHz] flux to the optical [4400 A] flux), optical magnitude, luminosity, and observing strategy. Objects with 10 > R > 1 were found to show a higher instance of microvariability than those with R < 1. This suggests that R = 1 is the appropriate cutoff between radio-loud and radio-quiet objects. A preference for low-redshift objects to display microvariability more often than higher redshift objects is seen; however, this is explainable via selection effects. We find a dependence in detection probability on observation length similar to that seen in radio-loud objects.

Evidence for a Population of Beamed Radio‐intermediate Quasars

Whether radio intermediate quasars possess relativistic jets as radio-loud quasars is an important issue in the understanding of the origin of radio emission in quasars. In this letter, using the two-epoch radio data obtained during Faint Image of Radio Sky at Twenty centimeter sky (FIRST) and NOAO VLA Sky Survey (NVSS), we identify 89 radio variable sources in the Sloan Digital Sky Survey. Among them, more than half are radio intermediate quasars (RL=f2cm/f2500A<250). For all objects with available multiple band radio observations, the radio spectra are either flat or inverted. The brightness temperature inferred from the variability is larger than the synchrotron-self Compton limit for a stationary source in 87 objects, indicating of relativistic beaming. Considering the sample selection and viewing angle effect, we conclude that relativistic jets probably exist in a substantianl fraction of radio intermediate quasars.

Radio Variability of Radio‐quiet and Radio‐loud Quasars

The majority of quasars are weak in their radio emission, with flux densities comparable to those in the optical, and energies far lower. A small fraction, about 10%, are hundreds to thousands of times stronger in the radio. Conventional wisdom holds that there are two classes of quasars, the radio-quiets and radio-louds, with a deficit of sources having intermediate power. Are there really two separate populations, and if so, is the physics of the radio emission fundamentally different between them? This paper addresses the second question, through a study of radio variability across the full range of radio power, from quiet to loud. The VLA was used during 10 epochs to study three carefully selected samples of 11 radio-quiet quasars, 11 radio-intermediate quasars, and 8 radio-loud quasars. A fourth sample consists of 20 VLA calibrators used for phase correction during the observations, all of which are radio-loud. The basic findings are that the root mean square amplitude of variability is independent of radio luminosity or radio-to-optical flux density ratio and that fractionally large variations can occur on timescales of months or less in both radio-quiet and radio-loud quasars. Combining this with similarities in other indicators, such as radio spectral index and the presence of VLBI-scale components, leads to the suggestion that the physics of radio emission in the inner regions of all quasars is essentially the same, involving a compact, partially opaque core together with a beamed jet. It is possible that differences in large-scale radio structures between radio-loud and radio-quiet quasars could stem from disruption of the jets in low-power sources before they can escape their host galaxies.

III Zw 2: Superluminal Motion and Compact Lobe Expansion in a Seyfert Galaxy

So far all relativistically boosted jets with superluminal motion have only been detected in normal radio galaxies that have early-type host galaxies. We have now discovered superluminal motion in the Seyfert 1 galaxy III Zw 2, classified as a spiral. Spectral and spatial evolution are closely linked. Since III Zw 2 is part of a sample of so-called radio-intermediate quasars (RIQ), it confirms earlier predictions of superluminal motion for this source, based on the argument that RIQs could be relativistically boosted jets in radio-weak quasars and Seyfert galaxies.

Millimeter-wave continuum observation of high-z radio quasars

Millimeter-wave continuum observations of high redshift (z3) radio loud quasars (RLQs) and radio intermediate quasars (RIQs) have been performed with the 45 m telescope of the Nobeyama Radio Observatory. Sixteen RLQs with S 5GHz > 200 mJy and nine RIQs with 200 mJy > S 5GHz > 20 mJy were observed at four millimeter-wave frequencies. All the observed quasars have synchrotron spectra and their possible dust emission component is obscured by the synchrotron emission in millimeter-wave frequencies, which can be explained by their strong AGN activities. Observed quasars are classified into three spectral classes, according to their millimeter-wave spectral index as steep spectrum, millimeter turn over and extreme flat spectrum quasars. Extreme flat spectrum quasars have relatively flat spectra up to 150 GHz, where the rest frequency is higher than 600 GHz. This is an indication that the objects are in very young stage of quasar evolution and shows higher nuclear activity than lower redshift quasars. One of the QSOs, 2358+189 previously known as a RIQ, is found to have extreme flat spectrum, and is now classified as RLQs.

The Nature of Radio‐Intermediate Quasars: What Is Radio‐loud and What Is Radio‐quiet?

We have performed quasi-simultaneous radio flux density measurements at 2.7 and 10 GHz for all Palomar-Green (PG) quasars with radio flux densities between 4 and 200 mJy. We find that a large fraction of these sources are variable, flat-spectrum quasars. This brings to 40% the total fraction of flat-spectrum quasars with a radio-to-optical flux ratio R > 10 in the PG quasar sample. We also find that the median R-parameter of these flat-spectrum quasars is lower than those of steep-spectrum quasars. This contradicts the predictions of the unified scheme and the idea that all flat-spectrum, core-dominated quasars are relativistically boosted lobe-dominated quasars. We show that this discrepancy is due to a population of flat-spectrum radio-intermediate quasars with 25 < R < 250 that can be explained neither as relativistically boosted quasars nor as normal radio-weak quasars. We point out that a natural explanation for the flat-spectrum radio-intermediate quasars is relativistic boosting in radio-weak quasars. If the flat-spectrum radio-intermediate quasars are considered the boosted counterparts to usual radio-weak quasars, their fraction among radio-weak quasars is roughly 10%, similar to the fraction of boosted quasars. This would point toward average Lorentz factors of γjet = 2–4 for and radio-weak quasars. The presence of the flat-spectrum radio-intermediate quasars changes the definition of radio-loud and can bias some conclusions drawn from optically selected quasar samples, where R 1–10 is used as the dividing line for both flat- and steep-spectrum quasars. Instead, one should use separate R-parameters for the dividing line in steep-spectrum (R 25) and flat-spectrum (R ~ 250) quasars.