Structure Of Quasars Research Articles

Efficient identification of broad absorption line quasars using dimensionality reduction and machine learning

Efficient identification of broad absorption line quasars using dimensionality reduction and machine learning

PS J2107−1611: A new wide-separation, quadruply imaged lensed quasar with flux ratio anomalies

We report the discovery of PS J2107−1611, a fold-configuration 4.3″-separation quadruply lensed quasar with a bright lensed arc. It was discovered using a convolutional neural network on Pan-STARRS gri images of pre-selected quasar candidates with multiple nearby Pan-STARRS detections. Spectroscopic follow-up with EFOSC2 on the ESO 3.58 m New Technology Telescope reveals the source to be a quasar at z = 2.673, with the blended fold image pair showing deformed broad lines relative to the other images. The flux ratios measured from optical to near-infrared imaging in the Canada-France-Hawaii Telescope Legacy Survey, Pan-STARRS, the Legacy Surveys, and the Vista Hemisphere Survey are inconsistent with a smooth mass model as the fold pair images are ∼15 times too faint. Variability, time delay effects, and reddening are ruled out through multiple-epoch imaging and color information. The system is marginally resolved in the radio in the Very Large Array Sky Survey S-band, where it has a 10 mJy detection. The radio flux ratios are compatible with the smooth mass macromodel. This system offers a unique tool for future studies of quasar structure with strong and microlensing. A more detailed analysis of follow-up with JWST/MIRI, VLT/MUSE, VLT/ERIS, and data from the European Very Long Baseline Interferometer will be presented in a forthcoming paper.

Ensemble mapping the inner structure of luminous quasars

ABSTRACT A simple prediction of the well-known unification model of active galactic nuclei is that a sample of sources should exhibit an anticorrelation between the solid angle of the dusty torus and of the ionization cone (as the sum of them shall equal 4π); however, this has never been detected. In this work, we analyse the correlation between the [O iii] 5007 narrow emission line equivalent width and LIR(λ)/Lbol for a large sample of luminous quasars. For the first time, we detect a clear intrinsic anticorrelation between them, which immediately verifies the torus/ionization-cone geometry in luminous quasars. More interestingly, the anticorrelation significantly weakens with increasing wavelength from ∼2 to 12 $\mu$m, and disappears at ∼12 $\mu$m. Simulations show that a cool dust component (in addition to the equatorial torus) with its strength positively correlating with the solid angle of the ionization cone is required to explain the observations. This shows that the polar dust seen in nearby active galaxies also exists in luminous quasars, with its contribution to total dust emission increasing with λ (from ∼2 to 12 $\mu$m) and reaching between 39 per cent and 62 per cent (model dependent) at rest frame 12 $\mu$m. Our findings provide a unique approach to map the otherwise spatially unresolvable inner structure of quasars.

Radio and mid-infrared properties of the blazar J1419–0838

The radio quasar NVSS J141922−083830 (J1419−0838) was initially classified as an uncategorised blazar-type object, following its detection in the gamma -ray band with the Fermi space telescope. Later, using multi-waveband observations and modeling, its was found to be a flat-spectrum radio quasar (FSRQ). However, its radio emission has never been discussed in depth in the literature. Here we present a detailed analysis on the radio properties of J1419−0838 using archival interferometric imaging data at pc and kpc scales. We conclude that the flux density variations, the flat radio spectrum, the compact nature of the quasar structure at all scales, and the relativistic Doppler enhancement of the radio emission all support the previous classification as an FSRQ. We also investigated the short- and long-term mid-infrared (MIR) light curve of the quasar based on observations by the Wide-field Infrared Survey Explorer satellite, and found that there is significant variability on time-scales of days as well as years. Comparison of the MIR light curve to the times of previously reported gamma -ray and optical flares shows no clear correlation between the events at different wavebands.

What are recent observations telling us in light of improved tests of distance duality relation?

As an exact result required by the Etherington reciprocity theorem, the cosmic distance duality relation (CDDR), η(z)=DL(z)(1+z)−2/DA(z)=1 plays an essential part in modern cosmology. In this paper, we present a new method (η(zi)/η(zj)) to use the measurements of ultra-compact structure in radio quasars (QSO) and the latest observations of type Ia supernova (SN Ia) to test CDDR. By taking the observations directly from SN Ia and QSOs, one can completely eliminate the uncertainty caused by the calibration of the absolute magnitudes of standard candles (MB) and the linear sizes of standard rulers (lm). Benefit from the absence of nuisance parameters involved in other currently available methods, our analysis demonstrates no evidence for the deviation and redshift evolution of CDDR up to z=2.3. The combination of our methodology and the machine learning Artificial Neural Network (ANN) would produce 10−3 level constraints on the violation parameter at high redshifts. Our results indicate perfect agreement between observations and predictions, supporting the persisting claims that the Etherington reciprocity theorem could still be the best description of our universe.

Revising the Hubble constant, spatial curvature and dark energy dynamics with the latest observations of quasars

In this paper we use a newly compiled sample of ultra-compact structure in radio quasars and strong gravitational lensing systems with quasars acting as background sources to constrain six spatially flat and non-flat cosmological models (ΛCDM, PEDE, and DGP). These two sets of quasar data (time-delay measurements of six strong lensing systems and 120 intermediate-luminosity quasars calibrated as standard rulers) could break the degeneracy between the cosmological parameters (H0, Ωm, and Ωk), and therefore provide more stringent cosmological constraints for the six cosmological models we study. A joint analysis of the quasar sample provides model-independent measurements of the Hubble constant H0, which are strongly consistent with that derived from the local distance ladder by the SH0ES collaboration in the ΛCDM and PEDE model. However, in the framework of the DGP cosmology (especially for a flat universe), the measured Hubble constant is in good agreement with that derived from the recent Planck 2018 results. In addition, our results show that zero spatial curvature is supported by the current lensed and unlensed quasar observations and that there is no significant deviation from a flat universe. For most of the cosmological models we study (flat ΛCDM, non-flat ΛCDM, flat PEDE, and non-flat PEDE), the derived matter density parameter is completely consistent with Ωm ∼ 0.30 in all the data sets, as expected based on the latest cosmological observations. Finally, according to the statistical deviance information criterion (DIC), the joint constraints provide substantial observational support to the flat PEDE model; however, they do not rule out dark energy being a cosmological constant and non-flat spatial hypersurfaces.

Constraining quasar structure using high-frequency microlensing variations and continuum reverberation

Gravitational microlensing is a powerful tool for probing the inner structure of strongly lensed quasars and for constraining parameters of the stellar mass function of lens galaxies. This is achieved by analysing microlensing light curves between the multiple images of strongly lensed quasars and accounting for the effects of three main variable components: (1) the continuum flux of the source, (2) microlensing by stars in the lens galaxy, and (3) reverberation of the continuum by the broad line region (BLR). The latter, ignored by state-of-the-art microlensing techniques, can introduce high-frequency variations which we show carry information on the BLR size. We present a new method that includes all these components simultaneously and fits the power spectrum of the data in the Fourier space rather than the observed light curve itself. In this new framework, we analyse COSMOGRAIL light curves of the two-image system QJ 0158-4325 known to display high-frequency variations. Using exclusively the low-frequency part of the power spectrum, our constraint on the accretion disk radius agrees with the thin-disk model estimate and the results of previous work where the microlensing light curves were fit in real space. However, if we also take into account the high-frequency variations, the data favour significantly smaller disk sizes than previous microlensing measurements. In this case, our results are only in agreement with the thin-disk model prediction only if we assume very low mean masses for the microlens population, i.e. ⟨M⟩ = 0.01 M⊙. At the same time, including the differentially microlensed continuum reverberation by the BLR successfully explains the high frequencies without requiring such low-mass microlenses. This allows us to measure, for the first time, the size of the BLR using single-band photometric monitoring; we obtain RBLR = 1.6−0.8+1.5 × 1017 cm, in good agreement with estimates using the BLR size–luminosity relation.

Revisiting the cosmic distance duality relation with machine learning reconstruction methods: the combination of HII galaxies and ultra-compact radio quasars

In this paper, we carry out an assessment of cosmic distance duality relation (CDDR) based on the latest observations of HII galaxies acting as standard candles and ultra-compact structure in radio quasars acting as standard rulers. Particularly, two machine learning reconstruction methods [Gaussian Process (GP) and Artificial Neural Network (ANN)] are applied to reconstruct the Hubble diagrams from observational data. We show that both approaches are capable of reconstructing the current constraints on possible deviations from the CDDR in the redshift range zsim 2.3. Considering four different parametric methods of CDDR, which quantify deviations from the CDDR and the standard cosmological model, we compare the results of the two different machine learning approaches. It is observed that the validity of CDDR is in well agreement with the current observational data within 1sigma based on the reconstructed distances through GP in the overlapping redshift domain. Moreover, we find that ultra-compact radio quasars could provide 10^{-3}-level constraints on the violation parameter at high redshifts, when combined with the observations of HII galaxies. In the framework of ANN, one could derive robust constraints on the violation parameter at a precision of 10^{-2}, with the validity of such distance duality relation within 2sigma confidence level.

ГУСТИНА СЕРЕДОВИЩА ВЕЛЕТЕНСЬКОЇ РАДІОСТРУКТУРИ ДЛЯ ГАЛАКТИК І КВАЗАРІВ З КРУТИМИ РАДІОСПЕКТРАМИ

Purpose: Estimate of the environment density of giant (with the linear size of about megaparsec) radio structures for galaxies and quasars with steep low-frequency spectra taken from the UTR-2 catalogue. Study of the cosmological evolution of environment density of giant radio sources. Determination of dependence of contribution of radio lobes into the emission of giant sources with respect to their environment density. Design/methodology/approach: We use the sample of sources from the UTR-2 catalogue of extragalactic sources to estimate the environment density for giant sources with steep low-frequency spectra. The selection criteria for the examined objects are the following: 1) the spectral index value is equal or larger than 1; 2) the fl ux density of emission at the frequency of 25 MHz is larger than 10 Jy; 3) the sample sources are optically identifi ed. The value of environment density of examined sources is obtained with the assumption of equality of source jet luminosity (at the synchrotron mechanism of radio emission) and its corresponding kinetic luminosity. The analysis of the estimates of environment densities is made for different classes of the sample objects (for galaxies and quasars with linear steep spectra and with break steep spectra). Findings: The estimates of environment density have been derived for giant radio structures formed by the jets of sources with steep spectrum from the UTR-2 catalogue. On the average, the environment density for the quasar structure (~ 10-28 g/sm3) is lesser than the one for the galaxies (~ 10-27 g/sm3 to ~ 10-26 g/sm3). The larger jet environment density is typical for the galaxies and quasars with the break steep spectra than for those with the linear steep spectra. The inverse power relation of the jet environment density and the source redshift (the cosmological evolution of the jet environment density) has been derived. The contribution of jet-related radio lobes into the emission of sources displays the inverse power relation for the environment density of the corresponding radio structures. Conclusions: The mean values of obtained estimates of environment density of giant jets of radio sources with steep low-frequency spectra indicate the lesser environment density of quasar jets than that for the galaxy jets. Giant radio sources with steep low-frequency spectrum (especially, with break steep spectrum) reveal considerable evolution of environment density of jets. The larger contribution of radio lobes (jets) into the emission of sources corresponds to the lesser environment density of sources taken from the UTR-2 catalogue. It can be due to propagation of jets (surrounded by radio lobes) from powerful radio sources to distances of about megaparsec, until the balance of source’s environment density and extragalactic environment density is reached. Key words: steep low-frequency radio spectrum; giant radio structure; jets; radio lobes; galaxies; quasars; environment density

Measurements of the Hubble constant and cosmic curvature with quasars: ultracompact radio structure and strong gravitational lensing

ABSTRACT Although the Hubble constant H0 and spatial curvature ΩK have been measured with very high precision, they still suffer from some tensions. In this paper, we propose an improved method to combine the observations of ultracompact structure in radio quasars and strong gravitational lensing with quasars acting as background sources to determine H0 and ΩK simultaneously. By applying the distance sum rule to the time-delay measurements of seven strong lensing systems and 120 intermediate-luminosity quasars calibrated as standard rulers, we obtain stringent constraints on the Hubble constant (H0 = 78.3 ± 2.9 km s−1 Mpc−1) and the cosmic curvature (ΩK = 0.49 ± 0.24). On the one hand, in the framework of a flat universe, the measured Hubble constant ($H_0=73.6^{+1.8}_{-1.6} \mathrm{\,km\,s^{-1}\,Mpc^{-1}}$) is strongly consistent with that derived from the local distance ladder, with a precision of 2 per cent. On the other hand, if we use the local H0 measurement as a prior, our results are marginally compatible with zero spatial curvature ($\Omega _K=0.23^{+0.15}_{-0.17}$) and there is no significant deviation from a flat universe. Finally, we also evaluate whether strongly lensed quasars would produce robust constraints on H0 and ΩK in the non-flat and flat Λ cold dark matter model, if the compact radio structure measurements are available from very long baseline interferometry observations.

Multiple Measurements of Quasars Acting as Standard Probes: Exploring the Cosmic Distance Duality Relation at Higher Redshift

Abstract General relativity reproduces main current cosmological observations, assuming the validity of the cosmic distance duality relation (CDDR) at all scales and epochs. However, CDDR is poorly tested in the redshift interval between the farthest observed Type Ia supernovae and that of the cosmic microwave background. We present a new idea of testing the validity of CDDR, through the multiple measurements of high-redshift quasars. Luminosity distances are derived from the relation between the UV and X-ray luminosities of quasars, while angular diameter distances are obtained from the compact structure in radio quasars. This will create a valuable opportunity where two different cosmological distances from the same kind of objects at high redshifts are compared. Our constraints are more stringent than other currently available results based on different observational data and show no evidence for the deviation from CDDR at z ∼ 3. Such an accurate model-independent test of fundamental cosmological principles can become a milestone in precision cosmology.

Precise Measurements of the Speed of Light with High-redshift Quasars: Ultra-compact Radio Structure and Strong Gravitational Lensing

Abstract Although the speed of light has been measured with very high precision, most of these measurements were carried out on Earth or in our close cosmic surroundings. In this Letter, we propose an original idea to combine the observations of ultra-compact structure in radio quasars and strong gravitational lensing with quasars acting as background sources to estimate the speed of light. The method will provide precise measurements of the speed of light using extragalactic objects at different redshifts. We evaluate if current or future missions such as the Large Synoptic Survey Telescope (LSST) and Dark Energy Survey (DES) can be sensitive enough to detect any variation of c. Our results show that strongly lensed quasars observed by LSST would produce robust constraints on Δc/c at the level of 10−4, if the compact radio structure measurements are available.

Spatially separated continuum sources revealed by microlensing in the gravitationally lensed broad absorption line quasar SDSS J081830.46+060138.0

Gravitational microlensing is a powerful tool for probing the inner structure of distant quasars. In this context, we have obtained spectropolarimetric observations of the two images of the broad absorption line (BAL) quasar SDSS J081830.46+060138.0 (J0818+0601) at redshift z ≃ 2.35. We first show that J0818+0601 is actually gravitationally lensed, and not a binary quasar. A strong absorption system detected at z = 1.0065 ± 0.0002 is possibly due to the lensing galaxy. Microlensing is observed in one image and it magnifies the emission lines, the continuum, and the BALs differently. By disentangling the part of the spectrum that is microlensed from the part that is not microlensed, we unveil two sources of continuum that must be spatially separated: a compact one, which is microlensed, and an extended one, which is not microlensed and contributes to two thirds of the total continuum emission. J0818+0601 is the second BAL quasar in which an extended source of rest-frame ultraviolet continuum is found. We also find that the images are differently polarized, suggesting that the two continua might be differently polarized. Our analysis provides constraints on the BAL flow. In particular, we find that the outflow is seen with a nonzero onset velocity, and stratified according to ionization.

КВАЗАР

An attempt is made to present a quasar structure based on the presence in its center of a supermassive object with an accretion disk, as well as the mechanisms for generating jet components and their initial segments. Model jet built on the basis of the allocation of the three main sources of matter supplied to the ejected jet. Such sources are: the baryonic matter of the accretion disk, the matter of the central body of the galaxy and dark galactic matter. Particles of dark matter — bosons — appear as a result of the pairwise combination of microwave photons, which are the remnant of stellar radiation. Deeper levels of matter (physical vacuum, or ether) are not taken into account, but their respective contributions are indicated in appropriate places. The central galactic body is considered an open system (dark star Mitchell - Laplace). This object has a finite size, finite density, and can have a large internal energy. Giving the central body the status of an open system allows one to overcome some difficult moments in the interpretation of observational data concerning the initial parts of the jet. The spatial separation of the original sources of matter makes it possible to speak of three components at the base of the jet of the active galactic nucleus.However, the appearance of a jet with three components requires certain conditions in the galactic core, which are not always there, but can occasionally appear. In addition, despite the fact that for the middle and central components of the jet the mechanism of their formation is the same, the central component of the jet may be absent. For its appearance, it is necessary that the energy and dynamic parameters of the central galactic body and the accretion disk satisfy certain conditions. Removing the restriction on the speed of motion of particles with a nonzero rest mass leads to a simple explanation of the presence of hard radiation from blazars and the appearance of excessively high energies of cosmic particles entering the earth's atmosphere. The consequences resulting from the mechanism of formation of two internal components of the jet are given.Two of them can be checked on the radiation of the central regions of nearby galaxies, and the other two consequences can relate to events on our planet — known major catastrophes and to the phenomenon sometimes observed in the Earth’s atmosphere

Black hole mass estimates in quasars

Context. The inter-line comparison between high- and low-ionization emission lines has yielded a wealth of information on the structure and dynamics of the quasar broad line region (BLR), including perhaps the earliest unambiguous evidence in favor of a disk + wind structure in radio-quiet quasars. Aims. We carried out an analysis of the C IVλ1549 and Hβ line profiles of 28 Hamburg-ESO high-luminosity quasars and of 48 low-z, low-luminosity sources in order to test whether the width of the high-ionization line C IVλ1549 could be correlated with Hβ and be used as a virial broadening estimator. Methods. We analyze intermediate- to high-S/N, moderate-resolution optical and near-infrared (NIR) spectra covering the redshifted C IVλ1549 and Hβ over a broad range of luminosity log L ∼ 44 − 48.5 [erg s−1] and redshift (0 − 3), following an approach based on the quasar main sequence. Results. The present analysis indicates that the line width of C IVλ1549 is not immediately offering a virial broadening estimator equivalent to Hβ. At the same time a virialized part of the BLR appears to be preserved even at the highest luminosities. We suggest a correction to FWHM(C IVλ1549) for Eddington ratio (using the C IVλ1549 blueshift as a proxy) and luminosity effects that can be applied over more than four dex in luminosity. Conclusions. Great care should be used in estimating high-L black hole masses MBH from C IVλ1549 line width. However, once a corrected FWHM C IVλ1549 is used, a C IVλ1549-based scaling law can yield unbiased MBH values with respect to the ones based on Hβ with sample standard deviation ≈0.3 dex.

CLOUDY View of the Warm Corona

Abstract Bright active galaxies show a range of properties, but many of these properties are correlated, which has led to the concept of the quasar main sequence. We test whether our current understanding of the quasar structure allows the pattern observed in the optical plane formed by the kinematic line width of Hβ and the relative importance of the Fe ii optical emission to be reproduced. We performed simulations of the Hβ and Fe ii production using the code CLOUDY and well-justified assumptions about the broadband spectra, distance to the emission line region, and the cloud properties. We show that the presence of the warm corona is an important element of the broadband spectrum, which decreases the dependence of the relative Fe ii emissivity on the Eddington ratio and allows the rare cases of particularly strong Fe ii emitters to be reproduced. Results are sensitive to the adopted cloud distance, and strong Fe ii emission can be obtained either by adopting strongly supersolar metallicity or a much shorter distance than traditionally obtained from reverberation mapping. We modeled in a similar way the UV plane defined by the Mg ii line and Fe ii UV pseudo-continuum, but here our approach is less successful, in general overproducing the Fe ii strength. We found that the Fe ii optical and UV emissivity depend in a different way on the turbulent velocity and metallicity, and the best extension of the model in order to cover both planes is to allow very large turbulent velocities in the broad-line region clouds.

Milliarcsecond compact structure of radio quasars and the geometry of the Universe

In this paper, by using the recently compiled set of 120 intermediate-luminosity quasars (ILQSO) observed in a single-frequency VLBI survey, we propose an improved model-independent method to probe cosmic curvature parameter $\Omega_k$ and make the first measurement of the cosmic curvature referring to a distant past, with redshifts up to $z\sim 3.0$. Compared with other methods, the proposed one involving the quasar data achieves constraints with higher precision in this redshift range. More importantly, our results indicate that the measured $\Omega_k$ is in good agreement with zero cosmic curvature, implying that there is no significant deviation from a flat Universe. Finally, we investigate the possibility of testing $\Omega_k$ with a much higher accuracy using quasars observed in the future VLBI surveys. It is shown that our method could provide a reliable and tight constraint on the prior $\Omega_k$ and one can expect the zero cosmic curvature to be established at the precision of $\Delta\Omega_k\sim 10^{-2}$ with 250 well-observed radio quasars.

A glimpse into the heart of a quasar

Astronomical objects called quasars have been difficult to study because of the limited spatial resolution of observations. An approach has been developed that allows the structure and dynamics of quasars to be investigated. Spatially resolved rotation of hot gas in a quasar.

High-resolution radio imaging of two luminous quasars beyond redshift 4.5

Context. Radio-loud active galactic nuclei in the early Universe are rare. The quasars J0906+6930 at redshift z = 5.47 and J2102+6015 at z = 4.57 stand out from the known sample with their compact emission on milliarcsecond (mas) angular scale with high (0.1 Jy level) flux densities measured at GHz radio frequencies. This makes them ideal targets for very long baseline interferometry (VLBI) observations. Aims. By means of VLBI imaging we can reveal the inner radio structure of quasars and model their brightness distribution to better understand the geometry of the jet and the physics of the sources. Methods. We present sensitive high-resolution VLBI images of J0906+6930 and J2102+6015 at two observing frequencies, 2.3 and 8.6 GHz. The data were taken in an astrometric observing programme involving a global five-element radio telescope array. We combined the data from five different epochs from 2017 February to August. Results. For one of the highest redshift blazars known, J0906+6930, we present the first-ever VLBI image obtained at a frequency below 8 GHz. Based on our images at 2.3 and 8.6 GHz, we confirm that this source has a sharply bent helical inner jet structure within ∼3 mas from the core. The quasar J2102+6015 shows an elongated radio structure in the east–west direction within the innermost ∼2 mas that can be described with a symmetric three-component brightness distribution model at 8.6 GHz. Because of their non-pointlike mas-scale structure, these sources are not ideal as astrometric reference objects. Our results demonstrate that VLBI observing programmes conducted primarily with astrometric or geodetic goals can be utilized for astrophysical purposes as well.

A joint microlensing analysis of lensing mass and accretion disc models

Microlensing of multiply imaged quasars is a unique probe of quasar structure, down to the size of the accretion disc and the central black hole. Flux ratios between close pairs of images of lensed quasars can be used to constrain the accretion disc size and temperature profile. The starting point of any microlensing model is the macromodel of the lens, which provides the convergence and shear values at the location of the multiple images. Here I present a new approach of microlensing modelling independently of the macromodel of the lens. The technique is applied to the close pair of images A1 and A2 of MG 0414+0534, for a set of flux ratios with large variation with respect to wavelength. The inferred accretion disc size and temperature profile measurements, as well as the smooth matter fraction at the location of the images, are quite robust under a wide range of macromodel variations. A case of using purely microlensing data (flux ratios) to constrain the macromodel is also presented. This is a first application of the technique on a fiducial system and set of flux ratios; the method is readily applicable to collections of such objects and can be extended to light curve and/or imaging data.