Flat-spectrum Radio-loud 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.

Scintillation is an indicator of astrometric stability

We examine the relationship between astrometric stability and astrophysical properties in flat-spectrum radio-loud quasars making up the celestial reference frame. We use position determinations from geodetic VLBI measurements, and develop a new metric for source position stability. We then compare this quantity to two measures of source compactness: structure index, which probes structure on milliarcsecond scales; and the presence of interstellar scintillation associated with the quasar, which probes scales of tens of microarcseconds. We find that persistent scintillators have greater position stability than episodic scintillators, which are in turn more stable than non-scintillators. Scintillators are also more likely to be compact on milliarcsecond scales, as measured by the structure index. Persistent scintillators are therefore excellent candidates for inclusion in any future realisation of the celestial reference frame. A list of these sources is presented in the Appendix. We find that slow (characteristic timescale >3 days) scintillators have more stable positions than rapid scintillators, suggesting they are more compact. High-cadence, long term monitoring is therefore required to identify other members of this population of compact, high brightness temperature quasars.

INCIDENCE OF Mg II ABSORPTION SYSTEMS TOWARD FLAT-SPECTRUM RADIO QUASARS

The conventional wisdom that the rate of incidence of Mg II absorption systems, dN/dz (excluding `associated systems' having velocity beta*c relative to the AGN of less than ~5000 km/s) is totally independent of the background AGN, has been challenged by a recent finding that dN/dz for strong Mg II absorption systems towards distant blazars is 2.2 \pm_{0.6}^{0.8} times the value known for normal optically-selected quasars (QSOs). This has led to the suggestion that a significant fraction of even the absorption systems with beta as high as 0.1 may have been ejected by the relativistic jets in the blazars, which are expected to be pointed close to our direction. Here we investigate this scenario using a large sample of 115 flat-spectrum radio-loud quasars (FSRQs) which too possess powerful jets, but are only weakly polarized. We show, for the first time, that dN/dz towards FSRQs is, on the whole, quite similar to that known for QSOs and the comparative excess of strong \mgii absorption systems seen towards blazars is mainly confined to beta< 0.15. The excess relative to FSRQs can probably result from a likely closer alignment of blazar jets with our direction and hence any gas clouds accelerated by them are more likely to be on the line of sight to the active quasar nucleus.

A New Approach for Estimating Kinetic Luminosity of Jet in AGNs

The K¨ onigl inhomogeneous jet model can successfully reproduce most observa- tional features of jets in active galactic nuclei (AGN), when suitable physical parameters are adopted. We improve K¨ onigl's calculations on the core emission from the jet with a small viewing angle �0 ∼ � (� is half opening angle of the conical jet). The proper motion of the jet component provides a constraint on the jet kinematics. Based on the inhomogeneous jet model, we use the proper motion data of the jet component to calculate the minimal kinetic luminosity of the jet required to reproduce the core emission measured by the very-long- baseline interferometry (VLBI) for a sample of BL Lac objects. Our results show that the minimal kinetic luminosity is slightly higher than the bolometric luminosity for most sources in the sample, which implies that radiatively inefficient accretion flows (RIAFs) may be in those BL Lac objects, or/and the properties of their broad-line regions (BLRs) are signifi- cantly different from flat-spectrum radio-loud quasars.

Orientation dependency of broad-line widths in quasars and consequences for black hole mass estimation

In this paper, we report new evidence that measurements of the broad-line widths in quasars are dependent on the source orientation, consistent with the idea that the broad-line region is flattened or disc like. This reinforces the view derived from radio-selected samples, where the radio-core dominance has been used as a measure of orientation. The results presented here show a highly significant (>99.95 per cent) correlation between radio spectral index (which we use as a proxy for source orientation) and broad-line width derived from the Hβ and Mg ii emission lines. This is the first time that this type of study has used quasars derived from a large optically selected quasar sample, where the radio-loud quasars (RLQs) and radio-quiet quasars (RQQs) have indistinguishable distributions in redshift, bolometric luminosity and colour, and therefore overcomes any biases which may be present in only selecting via radio emission. We find that the mean full width at half-maximum (FWHM) for the flat-spectrum (αrad≲ 0.5) radio-loud quasars (FSQs) to be ⁠, which differs significantly from the mean FWHM of the steep-spectrum (αrad > 0.5) radio-loud quasars (SSQs), where ⁠. We also find that the distribution in FWHM for the FSQs is indistinguishable from that of the RQQs, where ⁠. Considering other observational results in the literature, we interpret this result in the context of a significant fraction of the FSQs being derived from the underlying RQQ population which have their radio flux Doppler boosted above the RLQ/RQQ divide. Under the assumption of a disc-like broad-line region, we find no evidence for a difference in the average line-of-sight angle for RQQs and RLQs, implying that the difference is due to black hole mass. However, we caution against the virial method to estimate black hole masses in small or ill-defined quasar samples due to significant orientation dependencies. Disentangling the relative importance of black hole mass and orientation would require higher resolution radio observations. However, orientation effects could be minimized by obtaining low-frequency (<1 GHz) radio observations of the optically selected Sloan Digital Sky Survey (SDSS) quasars.

Evidence that powerful radio jets have a profound influence on the evolution of galaxies

The relationships between supermassive black holes and the properties of their associated dark-matter halos imply that outflows from accreting black holes provide a feedback mechanism regulating galaxy formation. Accreting black holes with weak or undetectable radio jets (radio-quiet quasars) outnumber those with powerful jets (radio-loud quasars) by a factor ~10-100, so powerful-jet outflows are often neglected. However, whenever powerful jets are triggered, there is a dramatic (factor >100) step-function increase in the efficiency of feedback. We use a feedback model, together with the measured space density of flat-spectrum radio-loud quasars, to show that a powerful-jet episode probably occurred in every protocluster in the Universe. Before jet triggering, there was time for gravitational collapse to create many (~10-100) surrounding protogalaxies massive enough to host radio-quiet quasars. After triggering, the powerful jet pushes back and heats ionized gas so that it cannot fall onto these protogalaxies and cool. Once neutral/molecular gas reservoirs become exhausted, there is a synchronized shut down in both star-formation and black-hole activity throughout the protocluster. These considerations imply that radio-loud quasars have a profound influence on the evolution of all the galaxies seen in clusters today.

On the black hole mass–radio luminosity relation for flat-spectrum radio-loud quasars

A new analysis of the connection between black hole mass and radio luminosity in radioselected flat-spectrum quasars (FSQs) is presented. In contrast to recent claims in the literature, we find no evidence that the black hole masses of radio-selected FSQs are systematically lower than those of luminous optically selected radio-loud quasars. The black hole masses of the FSQs are estimated via the virial black hole mass estimator which utilizes the linewidth of the Hβ emission line as a tracer of the central gravitational potential. By correcting for the inevitable effects of inclination, incurred as a result of the FSQs being viewed close to the line of sight, we find that the black hole masses of the FSQs with intrinsically powerful radio jets are confined, virtually exclusively, to Mbh > 10 8 M� . This is in good agreement with previous studies of optically selected FSQs and steep-spectrum radio-loud quasars. Finally, following the application of a realistic Doppler boosting correction, we find that the FSQs occupy a wide range in intrinsic radio luminosity, and that many sources would be more accurately classified as radio-intermediate or radio-quiet quasars. This range in radio luminosity suggests that the FSQs are fully consistent with an upper boundary on radio power of the form L 5 GHz ∝ M 2.5 bh .

The Evolution of the BL Lacertae Objects

The BL Lac population is set apart from the rest of the active galactic nuclei by a number of peculiar features, including remarkably little signs of cosmological evolution. We focus on this feature, and take hint from the observations to reconsider extraction of the primary energy from a Kerr hole via the Blandford-Znajek (BZ) process; in fact, we stress how this can power the emitting jets of the BL Lac objects in a regime of low accretion. We show that the timescale for the BZ process to exhaust the rotational energy of the hole spans many gigayears in all such sources. We compute scales long and uniform enough to yield an intrinsically slow population evolution, giving rise to number counts of ``Euclidean'' or flatter shape; even longer timescales apply to the additional, analogous process involving the inner accretion disk directly. Such slow evolution takes place in ambients and at epochs (z \lsim 1) where interactions of the host galaxies with companions become rare or weak. On the other hand, at higher z, we argue that frequent interactions of the hosts within groups enhanced, each for some 10^{-1} Gyr, the accretion rates and the emissions from the disks, attaining power levels that are typical of the radio-loud quasars. But such interactions were also likely to disorder the large-scale magnetic field in the disk and to decrease angular momentum of the hole, thus limiting the lifetime of all BZ emissions to under a few gigayears. Then the stronger evolution of the flat-spectrum radio-loud quasars was driven, similar to the radio-quiet ones, by the interaction rate decreasing rapidly with z.

X-ray properties of the Parkes sample of flat-spectrum radio sources: dust in radio-loud quasars?

We investigate the X-ray properties of the Parkes sample of Bat-spectrum radio sources using data from the ROSAT All-Sky Survey and archival pointed PSPC observations. In total, 163 of the 323 sources are detected. For the remaining 160 sources, 2 sigma upper limits to the X-ray flux are derived. We present power-law photon indices in the 0.1-2.4 keV energy band for 115 sources, which were determined either with a hardness ratio technique or from direct fits to pointed PSPC data if a sufficient number of photons were available. The average photon index is lGamma g = 1.95(-0.12)(+0.13) for flat-spectrum radio-loud quasars, lGamma g = 1.70(-0.24)(+0.23) for galaxies, and lGamma g = 2.40(-0.31)(+0.12) for BL Lac objects. The soft X-ray photon index is correlated with redshift and with radio spectral index in the sense that sources at high redshift and/or with flat (or inverted) radio spectra have flatter X-ray spectra on average. The results are in accord with orientation-dependent unification schemes for radio-loud active galactic nuclei. Webster et al. discovered many sources with unusually red optical continua among the quasars of this sample, and interpreted this result in terms of extinction by dust. Although the X-ray spectra in general do not show excess absorption, we find that low-redshift optically red quasars have significantly lower soft X-ray luminosities on average than objects with blue optical continua. The difference disappears for higher redshifts, as is expected for intrinsic absorption by cold gas associated with the dust. In addition, the scatter in log(f(x)/f(o)) is consistent with the observed optical extinction, contrary to previous claims based on optically or X-ray selected samples. Although alternative explanations for the red optical continua cannot be excluded with the present X-ray data, we note that the observed X-ray properties are consistent with the idea that dust plays an important role in some of the radio-loud quasars with red optical continua.

A unifying view of the spectral energy distributions of blazars

ABSTRA C T We collect data at well-sampled frequencies from the radio to the g-ray range for the following three complete samples of blazars: the Slew survey, the 1-Jy samples of BL Lacs and the 2-Jy sample of flat-spectrum radio-loud quasars (FSRQs). The fraction of objects detected in g-rays (E * 100 MeV) is ,17, 26 and 40 per cent in the three samples respectively. Except for the Slew survey sample, g-ray detected sources do not differ either from other sources in each sample, or from all the g-ray detected sources, in terms of the distributions of redshift, radio and X-ray luminosities or of the broad-band spectral indices (radio to optical and radio to X-ray). We compute average spectral energy distributions (SEDs) from radio to g-rays for each complete sample and for groups of blazars binned according to radio luminosity, irrespective of the original classification as BL Lac or FSRQ. The resulting SEDs show a remarkable continuity in that (i) the first peak occurs in different frequency ranges for different samples/luminosity classes, with most luminous sources peaking at lower frequencies; (ii) the peak frequency of the g-ray component correlates with the peak frequency of the lower energy one; (iii) the luminosity ratio between the high and low frequency components increases with bolometric luminosity. The continuity of properties among different classes of sources and the systematic trends of the SEDs as a function of luminosity favour a unified view of the blazar phenomenon: a single parameter, related to luminosity, seems to govern the physical properties and radiation mechanisms in the relativistic jets present in BL Lac objects as well as in FSRQs. The general implications of this unified scheme are discussed while a detailed theoretical analysis, based on fitting continuum models to the individual spectra of most g-ray blazars, is presented in a separate paper.

The Deep X-Ray Radio Blazar Survey. I. Methods and First Results

We have undertaken a survey, the Deep X-Ray Radio Blazar Survey (DXRBS), of archived, pointed ROSAT Position Sensitive Proportional Counter data for blazars by correlating the ROSAT WGACAT database with several publicly available radio catalogs, restricting our candidate list to serendipitous flat radio spectrum sources (αr ≤ 0.70, where Sν ∝ ν). We discuss our survey methods, identification procedure, and first results. Our survey is found to be ~95% efficient at finding flat-spectrum radio-loud quasars (FSRQs; 59 of our first 85 identifications) and BL Lacertae objects (22 of our first 85 identifications), a figure that is comparable to or greater than that achieved by other radio and X-ray survey techniques. The identifications presented here show that all previous samples of blazars (even when taken together) did not representatively survey the blazar population, missing critical regions of (LX, LR) parameter space within which large fractions of the blazar population lie. Particularly important is the identification of a large population of FSRQs (25% of DXRBS FSRQs) with ratios of X-ray to radio luminosity 10-6 (αrx 0.78). In addition, as a result of our greater sensitivity, the DXRBS has already more than doubled the number of FSRQs in complete samples with 5 GHz (radio) luminosities between 1031.5 and 1033.5 ergs s-1 Hz-1, and fills in the region of parameter space between X-ray–selected and radio-selected samples of BL Lac objects. The DXRBS is the very first sample to contain statistically significant numbers of blazars at low luminosities, approaching what should be the lower end of the FSRQ luminosity function.

Learning about Active Galactic Nucleus Jets from Spectral Properties of Blazars

We use multiwavelength spectra of core-dominated flat spectrum radio-loud quasars (FSRQs) to study properties of jets in active galactic nuclei. From a comparison of the predicted bulk Compton radiation with the observed soft X-ray fluxes, we find that these jets must be optically very thin. This eliminates the importance of such processes as Coulomb interactions, pair annihilation, and bremsstrahlung and determines the minimum distance from the black hole where a powerful jet can be fully developed (accelerated, collimated, and mass loaded). In the case of pair dominated jets, this distance is 100GMBH/c2. Further constraints on the parameters of a jet can be derived from luminosities and positions of spectral peaks of low-energy (IR/optical) and high-energy (γ-ray) radiation components, provided that both are produced by the same population of electrons. Whereas there appears to be a consensus about the synchrotron origin of the low-energy component, there is still debate about the mechanism of production of γ-rays. Most likely, they result from Comptonization of a soft radiation field by the same electrons that produce synchrotron radiation. Such a soft radiation field can be provided by the synchrotron process in a jet, by the accretion disk, and by a fraction of the disk radiation that is reprocessed/rescattered by emission line clouds, dust, and intercloud medium. We show that for FSRQs, the production of the high-energy radiation can be dominated by Comptonization of synchrotron radiation only for jets with moderate bulk Lorentz factors Γj (3) or if external radiation fields are much weaker than those observed in typical quasars. Furthermore, in synchrotron self-Compton (SSC) models, the relativistic plasma producing nonthermal radiation is constrained to be very weakly magnetized (B' < 0.01 gauss) and located at very large distances (r ~ 1019 cm). These can impose problems with jet confinement and with short observed timescale of variability. In the external radiation Compton (ERC) models, the magnetic fields are predicted to be much stronger (B' ~ 100 gauss), and nonthermal radiation can be produced very closely to the black hole (r ~ 1016 cm), which alleviates the problems with plasma confinement and short timescale variability. However, because of the close proximity to the black hole, the constraints imposed by the bulk Compton radiation imply that the plasma must be free of e+e- pairs. Finally, we discuss the difficulties that existing models have in explaining the sharp spectral breaks at MeV energies and postulate a hot version of the ERC scenario for the production of MeV peaks. We show that appropriate electron temperatures (kT ~ 100 MeV) to produce the luminosity peak at MeV energies by Comptonization of external UV radiation are achievable at subparsec distances only for proton-electron plasmas.

The X-ray Emission of Quasars as Observed by Ginga

We present preliminary results on a spectal analysis of quasars observed by the X-ray observatory Ginga. Simple power-law models with fixed Galactic absorbtion provide an adequate description of the spectra for most of the sources in the 2–18 keV band. A small number of sources show evidence for a feature at 6.4 keV (in the source rest frame) due to Fe line emission. Maximum likelihood and Spearman rank tests were used to investigate the relationship between radio loudness and X-ray spectral index in this class of object. These tests showed, respectively, that the mean X-ray spectral index of radio quiet quasars (RQQs) is significantly different from that of flat spectrum radio loud quasars (FRSQs) at the &gt;99% level, and that the dominant relationship with spectral index is radio loudness (not X-ray luminosity or redshift) at &gt;99% significance. This last result has not previously been demonstrated in this band, but agrees with findings in the lower energy Einstein band (0.5–3.5 keV). These results are discussed in the context of current unified models.

Continuum energy distribution of quasars - Shapes and origins

Continuum observations from ~0.3 nm to 6 cm (10^(9.7)-10^(18) Hz) are presented for 109 bright quasars from the Palomar-Green (PG) survey. Two-thirds of the quasars have been detected in the at wavelengths between 10 and 100 μm. All of the PG quasars appear to emit the bulk of their luminosity (typically more than 90%) between 3 nm and 300 μm (10^(12)-10^(17) Hz). The total luminosity at wavelengths longer than 1 μm is typically 20%-40% of that at wavelengths shortward of 1 μm. The gross shape of the energy distributions between 3 nm and 300 μm is remarkably similar for all the quasars except the flat-spectrum radio-loud quasars like 3C 273 and can plausibly be fitted by two broad components of thermal emission. In this interpretation the emission in the spectral range ~ 10 nm to 0.3 μm, the big blue bump, is dominated by 10,00-100,000 K thermal emission from an accretion disk. The emission between 2 μm and 1 mm, the infrared bump, is made up of reradiation from dust in a distorted disk extending from 0.1 pc to more than 1 kpc. The fairly small range in the relative sizes of the bumps suggests that the covering factor in most of the PG quasars is similar. There is no obvious connection between the strengths of the blue and peaks and whether or not the quasar is radio quiet or radio loud. The mass of emitting dust is estimated to be ~0.01 M_☉ at 2 μm and ~ 10^5 M_☉ at 60 μm. The radiation from 0.5 μm is thermal emission from the portion of the disk between 0.1 and 1 pc, illuminated primarily by the clouds of the broad-line region. The radiation from 5 μm to 1 mm is reradiation from a warped disk at distances greater than 1 pc from the central source, which is heated directly by radiation from the central source. Optically thin atomic emission (free-free and partially thermalized lines and bound-free) from gas within 1 pc of the central source, whose dust has sublimated, probably contributes to the flux from 0.5 to 2 μm. We believe that there is no convincing evidence for energetically significant nonthermal radiation in the wavelength range 3 nm to 300 μm in the continua of the radio-quiet and steep-spectrum radio-loud PG quasars.