Quasar Core Research Articles

CONSTRAINTS ON THE LOW-ENERGY CUTOFF IN THE ELECTRON DISTRIBUTION OF THE PKS 0637-752 JET

We reanalyze the Chandra ACIS spectrum of the kpc-scale jet in PKS 0637-752 to investigate the possible low-energy cutoff in the relativistic electron spectrum producing the nonthermal radiation in the scenario of inverse Compton (IC) emission off the cosmic microwave background. This was among the first objects targeted by the Chandra Observatory and gives a unique opportunity to study the low-energy X-ray emission free of detector contamination. As previously reported in the literature, the spectrum can be fit by a power law, with the slope predicted by the radio spectrum, modified by low energy absorption through the Galaxy as determined from the spectrum of the quasar core and by HI 21 cm observations. We obtain a marginally better fit with a model of IC emission produced by an electron population that exhibits a cutoff at γmin δ10 between about 50 and 80 (assuming Γ = δ). This range for γmin is higher than has previously been assumed in broadband spectral fits to the jet emission. The observed optical flux can be used to place a lower limit on γmin; the constraint is not very strong, but does suggest that γmin must be higher than 1 to avoid overproducing the optical emission. We investigate the effect of uncertainties in the column density for galactic absorption as well as the calibration of Chandra for these early observations. Finally, we discuss the implication of these limits on the jet luminosity in this source.

Dressing a Naked Quasar: Star Formation and Active Galactic Nucleus Feedback in HE 0450−2958

We present Australia Telescope Compact Array radio continuum observations of the quasar/galaxy system HE 0450-2958. An asymmetric triple linear morphology is observed, with the central radio component coincident with the quasar core and a second radio component associated with a companion galaxy at a projected distance of 7 kpc from the quasar. The system obeys the far-infrared to radio continuum correlation, implying that the radio emission is energetically dominated by star formation activity. However, there is undoubtedly some contribution to the overall radio emission from a low-luminosity active galactic nucleus (AGN) core and a pair of radio lobes. Long-baseline radio interferometric observations of the quasar core place a 3 ? upper limit of 0.6 mJy at 1400 MHz on the AGN contribution to the quasar's radio emission: less than 30% of the total. The remaining 70% of the radio emission from the quasar is associated with star formation activity and provides the first direct evidence of the quasar's host galaxy. A reanlaysis of the Very Large Telescope (VLT) spectroscopic data shows extended emission-line regions aligned with the radio axis and extended on scales of ~20 kpc. This is interpreted as evidence for jet-cloud interactions, similar to those observed in radio galaxies and Seyferts. The emission lines in the companion galaxy are consistent with radiative shocks, and its spatial association with the eastern radio lobe implies that large-scale jet-induced star formation has played a role in this galaxy's evolution.

Confronting X‐Ray Emission Models with the Highest Redshift Kiloparsec‐Scale Jets: Thez = 3.89 Jet in Quasar 1745+624

A newly identified kiloparsec-scale X-ray jet in the high-redshift z=3.89 quasar 1745+624 is studied with multi-frequency Very Large Array, Hubble Space Telescope, and Chandra X-ray imaging data. This is only the third large-scale X-ray jet beyond z > 3 known and is further distinguished as being the most luminous relativistic jet observed at any redshift, exceeding 10{sup 45} erg/s in both the radio and X-ray bands. Apart from the jet's extreme redshift, luminosity, and high inferred equipartition magnetic field (in comparison to local analogues), its basic properties such as X-ray/radio morphology and radio polarization are similar to lower-redshift examples. Its resolved linear structure and the convex broad-band spectral energy distributions of three distinct knots are also a common feature among known powerful X-ray jets at lower-redshift. Relativistically beamed inverse Compton and ''non-standard'' synchrotron models have been considered to account for such excess X-ray emission in other jets; both models are applicable to this high-redshift example but with differing requirements for the underlying jet physical properties, such as velocity, energetics, and electron acceleration processes. One potentially very important distinguishing characteristic between the two models is their strongly diverging predictions for the X-ray/radio emission with increasing redshift. This is considered, though with the limited sample of three z > 3 jets it is apparent that future studies targeted at very high-redshift jets are required for further elucidation of this issue. Finally, from the broad-band jet emission we estimate the jet kinetic power to be no less than 10{sup 46} erg/s, which is about 10% of the Eddington luminosity corresponding to this galaxy's central supermassive black hole mass M{sub BH} {approx}> 10{sup 9} M{sub {circle_dot}} estimated here via the virial relation. The optical luminosity of the quasar core is about ten times over Eddington, hence the inferred jet power seems to be much less than that available from mass accretion. The apparent super-Eddington accretion rate may however suggest contribution of the unresolved jet emission to the observed optical flux of the nucleus.

ChandraObservations of Magnetic Fields and Relativistic Beaming in Four Quasar Jets

We discuss the physical properties of four quasar jets imaged with the Chandra X-Ray Observatory in the course of a survey for X-ray emission from radio jets (Marshall et al.). These objects have sufficient counts to study their spatially resolved properties, even in the 5 ks survey observations. We have acquired Australia Telescope Compact Array data with resolution matching Chandra. We have searched for optical emission with Magellan, with subarcsecond resolution. The radio to X-ray spectral energy distribution for most of the individual regions indicates against synchrotron radiation from a single-component electron spectrum. We therefore explore the consequences of assuming that the X-ray emission is the result of inverse Compton scattering on the cosmic microwave background. If particles and magnetic fields are near minimum energy density in the jet rest frames, then the emitting regions must be relativistically beamed, even at distances of order 500 kpc from the quasar. We estimate the magnetic field strengths, relativistic Doppler factors, and kinetic energy flux as a function of distance from the quasar core for two or three distinct regions along each jet. We develop, for the first time, estimates in the uncertainties in these parameters, recognizing that they are dominated by our assumptions in applying the standard synchrotron minimum energy conditions. The kinetic power is comparable with, or exceeds, the quasar radiative luminosity, implying that the jets are a significant factor in the energetics of the accretion process powering the central black hole. The measured radiative efficiencies of the jets are of order 10-4.

Relative variations of the physical parameters of variable extragalactic radio sources

A method for studying the physical conditions in compact components of extragalactic radio sources displaying variability on time scales of hundreds of days is proposed. The method can be used to estimate the relative variations of the magnetic-field strength and number density of relativistic electrons in superluminal jets from the cores of quasars and radio galaxies. Results are presented for the jets of the quasars 3C 120, 3C 273, 3C 279, and 3C 345. The energies of the magnetic field and relativistic particles in these objects are not in equipartition. As a rule, the magnetic-field strength decreases appreciably during the evolution of an expanding jet, while the number of relativistic electrons grows.

Molecular Gas at High Redshift: Jet-induced Star Formation?

We present an alternative interpretation of the observations of BR 1202-0725 at z = 4.695 and show that its properties are consistent with a relativistic jet issuing from the quasar core, propagating into the intergalactic medium, and triggering star formation along its path. Prompted by this finding, we reviewed all the z > 3 objects detected in molecular line emission and found that the distribution of gas and dust in these sources is often spatially or kinematically offset from the host galaxy and preferentially aligned along the radio axis. These observations suggest to us a scenario in which CO emission observed in high-redshift galaxies is located where it forms: along the sites of star formation triggered initially by relativistic jets.

Obscured Binary Quasar Cores in SDSS J104807.74+005543.5?

We report the discovery of a possible close binary system of quasars in SDSS J1048+0055. The [OIII]4959,5007 emission lines are clearly double-peaked, and two discrete radio sources with a projected physical separation of ~20 pc are found in the VLBA milliarcsec resolution image at 8.4 GHz. Each of the [O III]4959,5007 doublets and Hbeta can be well modelled by two Gaussians and the line ratio, [O III]5007/Hbeta ~7, is typical of Seyfert 2 galaxies. No broad component of Hbeta was detected and its [O III]5007 luminosity, L_[OIII] ~ 9.2 times 10^42 erg s^-1, is comparable to luminous quasars and is a few ten times more luminous than typical Seyfert galaxies. One natural interpretation is that SDSS J1048+0055 contains two close quasar-like nuclei and the BLR around them are obscured. Other possible models are also discussed. We suggest that double-peaked narrow emission line profile may be an effective way of selecting candidates of binary black holes with intermediate separation.

VLT + UVES spectroscopy of the low-ionization intrinsic absorber in SDSS J001130.56+005550.7

We analyse high-resolution VLT+UVES spectra of the low-ionization intrinsic absorber observed in the BAL QSO SDSS J001130.56+005550.7. Two narrow absorption systems at velocities -600 km s-1 and -22 000 km s-1 are detected. The low-velocity system is part of the broad absorption line (BAL), while the high-velocity one is well detached. While most narrow absorption components are only detected in the high-ionization species, the lowest velocity component is detected in both high- and low-ionization species, including in the excited and lines. From the analysis of doublet lines, we find that the narrow absorption lines at the low-velocity end of the BAL trough are completely saturated but do not reach zero flux, their profiles being dominated by a velocity-dependent covering factor. The covering factor is significantly smaller for than for and , which demonstrates the intrinsic nature of absorber. From the analysis of the excited and lines in the lowest velocity component, we find an electron density 103 cm-3. Assuming photoionization equilibrium, we derive a distance 20 kpc between the low-ionization region and the quasar core. The correspondence in velocity of the high- and low-ionization features suggests that all these species must be closely associated, hence formed at the same distance of ~20 kpc, much higher than the distance usually assumed for BAL absorbers.

Extended X-ray emission in the high-redshift quasar GB 1508+5714 at z = 4.3

We report the discovery of extended X-ray emission around the powerful high-redshift quasar GB 1508+5714 at z=4.3, revealed in a long Chandra ACIS observation. The emission feature is 3-4 arcsec away from the quasar core, which corresponds to a projected distance of about 25 kpc. The X-ray spectrum is best fitted with a power law of photon index 1.92+-0.35 (90 per cent c.l.). The X-ray flux and luminosity reach 9.2x10^-15 ergs (0.5-8 keV) and 1.6x10^45 erg s^-1 (2.7-42.4 keV rest frame, Omega_Lambda=0.73, Omega_m=0.27, H_0=71 km s^-1 Mpc^-1), which is about 2 percent of the total X-ray emission of the quasar. We interpret the X-ray emission as inverse Compton scattering of Cosmic Microwave Background photons. The scattering relativistic electron population could either be a quasi-static diffuse cloud fed by the jet, or an outer extension of the jet with a high bulk Lorentz factor. We argue that the lack of an obvious detection of radio emission from the extended component could be a consequence of Compton losses on the electron population, or of a low magnetic field. Extended X-ray emission produced by inverse Compton scattering may be common around high redshift radio galaxies and quasars, demonstrating that significant power is injected into their surrounding by powerful jets.

Radio-ExcessIRASGalaxies: PMN/FSC Sample Selection

A sample of 178 extragalactic objects is defined by correlating the 60 μm IRAS Faint Source Catalog (FSC) with the 5 GHz Parkes-MIT-NRAO (PMN) catalog. Of these, 98 objects lie above the radio/far-infrared relation for radio-quiet objects. These radio-excess galaxies and quasars have a uniform distribution of radio excesses, with no evidence for a radio-loud correlation equivalent to the well-known radio-quiet radio/far-infrared relation. The radio-intermediate objects appear to be a new population of active galaxies not present in previous radio/far-infrared samples chosen using more stringent far-infrared criteria. The radio-excess objects extend over the full range of far-infrared luminosities seen in extragalactic objects, from low-luminosity galaxies with νLν(60 μm) < 109 L⊙ to ultraluminous infrared galaxies with νLν(60 μm) > 1012 L⊙. Objects with small radio excesses are more likely to have far-infrared colors similar to starbursts, while objects with large radio excesses have far-infrared colors typical of pure AGNs. Some of the most far-infrared luminous radio-excess objects have the highest far-infrared optical depths. These are good candidates to search for hidden broad-line regions in polarized light or via near-infrared spectroscopy. Some low far-infrared luminosity radio-excess objects appear to derive a dominant fraction of their far-infrared emission from star formation, despite the dominance of the AGN at radio wavelengths. Many of the radio-excess objects have sizes likely to be smaller than the optical host but show optically thin radio emission, rather than flat radio spectra indicative of compact quasar cores. We draw parallels between these objects and high radio luminosity compact steep-spectrum and gigahertz peaked-spectrum objects. Radio sources with these characteristics may be young AGNs in which the radio activity has begun only recently. Alternatively, high central densities in the host galaxies may be confining the radio sources to compact sizes. We discuss future observations required to distinguish between these possibilities and determine the nature of radio-excess objects.

An X-Ray Jet Discovered by Chandra in the z =4.3 Radio-selected Quasar GB 1508+5714

We report the Chandra discovery of an X-ray jet associated with the z = 4.3 radio-loud quasar GB 1508+5714. The jet X-ray emission peaks ~2'' to the southwest of the quasar core. We present archival Hubble Space Telescope Wide Field Planetary Camera 2 data of the quasar field that show no optical emission at the location of the X-ray jet. We discuss possible emission mechanisms and give constraints to the magnetic field and energy densities for synchrotron radiation or for Compton scattering of the cosmic microwave background radiation as the jet X-ray emission process.

Submillimeter Observations of a Sample of Broad Absorption Line Quasars

The broad absorption line (BAL) features seen in a small fraction of quasar optical/UV spectra are attributed to bulk outflows away from the quasar core. Observations suggest that dust plays a key role in these systems, although whether the inferred dust properties are a signature of orientation effects or whether they are indicative of an evolutionary sequence remains an outstanding issue. Submillimeter detections of BAL quasars (BALQSOs), which would clearly help to resolve this issue, have so far been sparse. This Letter reports on new submillimeter observations of seven BALQSOs. The strongest influence on the observed flux is found to be the redshift, with the two highest redshift sources appearing intrinsically more submillimeter-luminous than the lower redshift ones. Since this trend is also seen in other high-redshift active galactic nuclei (AGNs), including non-BAL quasars, it implies that the dust emission properties of these systems are no different from those of the general AGN population, which is difficult to reconcile with the evolutionary interpretation of the BAL phenomenon.

VLBI Polarimetry of 177 Sources from the Caltech–Jodrell Bank Flat‐Spectrum Survey

We present Very Long Baseline Array observations and a statistical analysis of 5 GHz VLBI polarimetry data from 177 sources in the Caltech-Jodrell Bank Flat-Spectrum (CJF) survey. The CJF survey, a complete, flux density-limited sample of 293 extragalactic radio sources, gives us the unique opportunity to compare a broad range of source properties for quasars, galaxies, and BL Lacertae objects. We focus primarily on jet properties, specifically, the correlation between the jet axis angle and the polarization angle in the core and jet. A strong correlation is found for the electric vector polarization angle in the cores of quasars to be perpendicular to the jet axis. Contrary to previous claims, no correlation is found between the jet polarization angle and the jet axis in either quasars or BL Lac objects. With this large, homogeneous sample we are also able to investigate cosmological issues and active galactic nucleus evolution.

Chandraobservations of nuclear X-ray emission from a sample of radio sources

We present the X-ray properties of a sample of 17 radio sources observed with the Chandra X-ray Observatory as part of a project aimed at studying the X-ray emission from their radio jets. In this paper, we concentrate on the X-ray properties of the unresolved cores. The sample includes 16 quasars (11 core-dominated and 5 lobe-dominated) in the redshift range z= 0:30-1.96, and one low-power radio-galaxy at z= 0:064. No diuse X-ray emission is present around the cores of the quasars, except for the nearby low-power galaxy that has diuse emission on a scale and with a luminosity consistent with other FRIs. No high-amplitude, short-term variability is detected within the relatively short Chandra exposures. However, 1510 089 shows low-amplitude flux changes with a timescale of 25 min. The X-ray spectra of the quasar cores are generally well described by a single power law model with Galactic absorption. However, in six quasars we find soft X-ray excess emission below 1.6 keV. Interestingly, we detect an Fe K-shell emission line, consistent with fluorescent K emission from cold iron, in one lobe- and two core-dominated sources. The average X-ray photon index for the quasars in the sample is sample= 1:66 and dispersionsample= 0:23. The average spectral slope for our sample is flatter than the slope found for radio-quiet quasars and for radio-loud AGNs with larger jet orientations; this indicates that beaming aects the X-ray emission from the cores in our sample of quasars.

On the relativistic beaming and orientation effects in core-dominated quasars

In this paper, we investigate the relativistic beaming effects in a well-defined sample of core-dominated quasars using the correlation between the relative prominence of the core with respect to the extended emission (defined as the ratio of core-to lobe-flux density measured in the rest frame of the source) and the projected linear size as an indicator of relativistic beaming and source orientation. Based on the orientation-dependent relativistic beaming and unification paradigm for high luminosity sources in which the Fanaroff-Riley class-II radio galaxies form the unbeamed parent population of both the lobe- and core-dominated quasars which are expected to lie at successively smaller angles to the line of sight, we find that the flows in the cores of these core-dominated quasars are highly relativistic, with optimum bulk Lorentz factor,γ opt∼ 6–16, and also highly anisotropic, with an average viewing angle, ∼ 9°–16°. Furthermore, the largest boosting occurs within a critical cone angle of ≈ 4°–10°.

ChandraDiscovery of a 300 Kiloparsec X‐Ray Jet in the Gigahertz‐peaked Spectrum Quasar PKS 1127−145

We have discovered an X-ray jet with Chandra imaging of the z=1.187 radio-loud quasar PKS1127-145. In this paper we present the Chandra X-ray data, follow-up VLA observations, and optical imaging using the HST WFPC2. The X-ray jet contains 273+/-5 net counts in 27ksec and extends ~30 arcsec, from the quasar core, corresponding to a minimum projected linear size of ~330/h_50 kpc. The evaluation of the X-ray emission processes is complicated by the observed offsets between X-ray and radio brightness peaks. We discuss the problems posed by these observations to jet models. In addition, PKS1127-145 is a Giga-Hertz Peaked Spectrum radio source, a member of the class of radio sources suspected to be young or ``frustrated'' versions of FRI radio galaxies. However the discovery of an X-ray and radio jet extending well outside the host galaxy of PKS1127-145 suggests that activity in this and other GPS sources may be long-lived and complex.

Resolved nuclear CO(1-0) emission in APM 08279+5255: gravitational lensing by a naked cusp?

The ultraluminous broad absorption line quasar APM 08279+5255 is one of the most luminous systems known. Here, we present an analysis of its nuclear CO(1–0) emission. Its extended distribution suggests that the gravitational lens in this system is highly elliptical, probably a highly inclined disc. The quasar core, however, lies in the vicinity of a naked cusp, indicating that APM 08279+5255 is truly the only odd-image gravitational lens. This source is the second system for which the gravitational lens can be used to study structure on sub-kiloparsec scales in the molecular gas associated with the AGN host galaxy. The observations and lens model require CO distributed on a scale of ∼400 pc. Using this scale, we find that the molecular gas mass makes a significant, and perhaps dominant, contribution to the total mass within a couple of hundred parsecs of the nucleus of APM 08279+5255.

Statistical tests of the unification scheme for high luminosity double radio sources

We have carried out some statistical tests of relativistic beaming and radio source orientation scenarios using the core dominance parameter Rand linear size D of a recent sample of double-lobed quasars and radio galaxies as orientation indicators. Our results show that the maximum Doppler boosting occurs within a cone angle of ∼ 13°corresponding to an optimum Lorentz factor of ∼ 5. On the average, quasar cores appear to be boosted by a factor of ∼ 10 relative to those of radio galaxies. In general, we found that quasars lie at closer angles to the line of sight than radio galaxies with median values of 28° and 51°respectively, implying a relative foreshortening factor of ∼ 2. These results are consistent with the simple relativistic beaming and orientation-based unification hypotheses in which quasars are the beamed counterparts of powerful radio galaxies which form the isotropic parent population. The results show a strong evidence that orientation of source axis with respect to the line of sight is a crucial parameter in the classification schemes for radio sources.

Very Long Baseline Array Polarimetry of Three Powerful Radio Galaxy Cores

We present sensitive, high dynamic range, Very Long Baseline Array (VLBA) polarimetric observations of the cores of three powerful radio galaxies: 3C 166, 3C 236, and 3C 390.3. Significant polarization is detected in one source (3C 166) allowing us to map out the Faraday rotation measure (RM) distribution and projected magnetic field direction. The inner jet of 3C 166 is found to have a rest frame RM of -2300 rad m-2, similar to those found in quasar cores. No polarized flux was detected from the other two sources, but in both, counterjets are seen. The counterjet in 3C 236 was previously known, but the detection in 3C 390.3 is a new discovery. We suggest that the low fractional polarization in radio galaxy cores is the result of Faraday depolarization by ionized gas associated with the accretion disk. The lower polarization of radio galaxy cores compared to quasars is then naturally explained by unified models as a result of the viewing angle.

Microlensing of Broad Absorption Line Quasars: Polarization Variability

ABSTRACTRoughly 10% of all quasars exhibit broad absorption line (BAL) features which appear to arise in material outflowing at high velocity from the active galactic nucleus. The details of this outflow are, however, very poorly constrained, and the particular nature of the BAL material is essentially unknown. Recently, new clues have become available through polarimetric studies, which have found that BAL troughs are more polarized than the quasar continuum radiation. To explain these observations, researchers have developed models where the BAL material outflows equatorially across the surface of the dusty torus. In these models, however, several sources of the BAL polarization are possible. Here we demonstrate how polarimetric monitoring of gravitationally lensed quasars, such as H1413+117, during microlensing events not only can distinguish between two currently popular models but also can provide further insight into the structure at the cores of BAL quasars.