- ID:
- ivo://CDS.VizieR/J/MNRAS/466/3088
- Title:
- Lensed and extended quasars
- Short Name:
- J/MNRAS/466/3088
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Wide-field photometric surveys enable searches of rare yet interesting objects, such as strongly lensed quasars or quasars with a bright host galaxy. Past searches for lensed quasars based on their optical and near-infrared properties have relied on photometric cuts and spectroscopic preselection (as in the Sloan Quasar Lens Search), or neural networks applied to photometric samples. These methods rely on cuts in morphology and colours, with the risk of losing many interesting objects due to scatter in their population properties, restrictive training sets, systematic uncertainties in catalogue-based magnitudes and survey-to-survey photometric variations. Here, we explore the performance of a Gaussian mixture model to separate point-like quasars, quasars with an extended host and strongly lensed quasars using grizpsf and model magnitudes and WISEW1, W2. The choice of optical magnitudes is due to their presence in all current and upcoming releases of wide-field surveys, whereas UV information is not always available. We then assess the contamination from blue galaxies and the role of additional features such as W3 magnitudes or psf-model terms as morphological information. As a demonstration, we conduct a search in a random 10 per cent of the SDSS footprint, and provide the catalogue of the 43 SDSS object with the highest 'lens' score in our selection that survive visual inspection, and are spectroscopically confirmed to host active nuclei. We inspect archival data and find images of 5/43 objects in the Hubble Legacy Archive, including two known lenses.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/616/A118
- Title:
- Lensed QSOs light curves & spectral monitoring
- Short Name:
- J/A+A/616/A118
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In the framework of the Gravitational LENses and DArk MAtter (GLENDAMA) project, we present a database of nine gravitationally lensed quasars (GLQs) that have two or four images brighter than r=20mag and are located in the northern hemisphere. This new database consists of a rich variety of follow-up observations included in the GLENDAMA global archive, which is publicly available online and contains 6557 processed astronomical frames of the nine lens systems over the period 1999-2016. In addition to the GLQs, our archive also incorporates binary quasars, accretion-dominated radio-loud quasars, and other objects, where about 50% of the non-GLQs were observed as part of a campaign to identify GLQ candidates. Most observations of GLQs correspond to an ongoing long-term macro-programme with 2-10m telescopes at the Roque de los Muchachos Observatory, and these data provide information on the distribution of dark matter at all scales. We outline some previous results from the database, and we additionally obtain new results for several GLQs that update the potential of the tool for astrophysical studies.
- ID:
- ivo://CDS.VizieR/J/AJ/130/1389
- Title:
- Linear polarization of AGN jets at 15GHz
- Short Name:
- J/AJ/130/1389
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present first-epoch, milliarcsecond-scale linear polarization images at 15GHz of 133 jets associated with active galactic nuclei (AGNs) from the MOJAVE (Monitoring of Jets in Active Galactic Nuclei with VLBA Experiments) survey. MOJAVE is a long-term observational program to study the structure and evolution of relativistic outflows in AGNs. The sample consists of all known AGNs with Galactic latitude |b|>2.5{deg}, J2000.0 declination greater than -20{deg} and correlated 15GHz Very Long Baseline Array (VLBA) flux density exceeding 1.5Jy (2Jy for sources below the celestial equator) at any epoch during the period 1994-2003.
- ID:
- ivo://CDS.VizieR/J/A+A/631/A49
- Title:
- LOFAR images of blazar S5 0836+710
- Short Name:
- J/A+A/631/A49
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The emission and proper motion of the terminal hotspots of active galactic nucleus (AGN) jets can be used as a powerful probe of the intergalactic medium. However, measurements of hotspot advance speeds in active galaxies are difficult, especially in the young universe, because of the low angular velocities and the low brightness of distant radio galaxies. Our goal is to study the termination of an AGN jet in the young universe and to deduce physical parameters of the jet and the intergalactic medium. We used the LOw Frequency ARray (LOFAR) to image the long-wavelength radio emission of the high-redshift blazar S5 0836+710 on arcsecond scales between 120MHz and 160MHz. The LOFAR image shows a compact unresolved core and a resolved emission region about 1.5 arcsec to the southwest of the radio core. This structure is in general agreement with previous higher-frequency radio observations with the Multi-Element Radio-Linked Interferometer Network (MERLIN) and the Very Large Array (VLA). The southern component shows a moderately steep spectrum with a spectral index of about >~-1,and the spectral index of the core is flat to slightly inverted. In addition, we detect for the first time a resolved steep-spectrum halo with a spectral index of about -1 surrounding the core. The arcsecond-scale radio structure of S5 0836+710 can be understood as a Faranoff-Riley (FR) II radio galaxy observed at a small viewing angle. The southern component can be interpreted as the region of the approaching jet's terminal hotspot, and the halo like diffuse component near the core can be interpreted as the counter-hotspot region. From the differentialDoppler boosting of both features, we can derive the hotspot advance speed to (0.01-0.036)c. Ata constant advance speed, the derived age of the source would exceed the total lifetime of such a powerful FR II radio galaxy substantially. Thus, the hotspot advance speed must have been higher in the past, in agreement with a scenario in which the originally highly relativistic jet has lost collimation as a result of instability growth and has transformed into an only mildly relativistic flow. Our data suggest that the density of the intergalactic medium around this distant (z=2.22) AGN could be substantially higher than the values typically found in less distant FR II radio galaxies.
- ID:
- ivo://CDS.VizieR/J/A+A/587/A112
- Title:
- Long term R and V band monitoring of AGN
- Short Name:
- J/A+A/587/A112
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Gaia astrometric mission of the European Space Agency was launched on December 2013. It will provide a catalog of 500 000 quasars. Some of these targets will be chosen to build an optical reference system that will be linked to the International Celestial Reference Frame (ICRF). The astrometric coordinates of these sources will have roughly the same uncertainty at both optical and radio wavelengths, and it is then mandatory to observe a common set of targets to build the link. In the ICRF, some targets have been chosen because of their pointlikeness. They are quoted as defining sources, and they ensure very good uncertainty about their astrometric coordinates. At optical wavelengths, a comparable uncertainty could be achieved for targets that do not exhibit strong astrophysical phenomena, which is a potential source of photocenter flickering. A signature of these phenomena is a magnitude variation at optical wavelengths. The goal of this work is to present the time series of 14 targets suitable for the link between the ICRF and the future Gaia Celestial Reference Frame. The observations have been done systematically by robotic telescopes in France and Chile once every two nights since 2011 and in two filters. These time series are analyzed to search for periodic or quasi-periodic phenomena that must be taken into account when computing the uncertainty about the astrometric coordinates. Two independent methods were used in this work to analyze the time series. We used the CLEAN algorithm to compare the frequency obtained to those given by the Lomb-Scargle method. It avoids misinterpreting the frequency peaks given in the periodograms.
- ID:
- ivo://CDS.VizieR/J/A+A/622/A11
- Title:
- LoTSS/HETDEX. Optical quasars. I.
- Short Name:
- J/A+A/622/A11
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The radio-loud/radio-quiet (RL/RQ) dichotomy in quasars is still an open question. Although it is thought that accretion onto supermassive black holes in the centre the host galaxies of quasars is responsible for some radio continuum emission, there is still a debate as to whether star formation or active galactic nuclei (AGN) activity dominate the radio continuum luminosity. To date, radio emission in quasars has been investigated almost exclusively using high-frequency observations in which the Doppler boosting might have an important effect on the measured radio luminosity, whereas extended structures, best observed at low radio frequencies, are not affected by the Doppler enhancement. We used a sample of quasars selected by their optical spectra in conjunction with sensitive and high-resolution low-frequency radio data provided by the LOw Frequency ARray (LOFAR) as part of the LOFAR Two-Metre Sky Survey (LoTSS) to investigate their radio properties using the radio loudness parameter (R=L_144MHz_/L_iband_). The examination of the Li band radio continuum emission and RL/RQ dichotomy in quasars exhibits that quasars show a wide continuum of radio properties (i.e. no clear bimodality in the distribution of R). Radio continuum emission at low frequencies in low-luminosity quasars is consistent with being dominated by star formation. We see a significant albeit weak dependency of R on the source nuclear parameters. For the first time, we are able to resolve radio morphologies of a considerable number of quasars. All these crucial results highlight the impact of the deep and high-resolution low-frequency radio surveys that foreshadow the compelling science cases for the Square Kilometre Array (SKA).
- ID:
- ivo://CDS.VizieR/J/ApJS/213/3
- Title:
- Low-frequency flat spectrum sources (LORCAT)
- Short Name:
- J/ApJS/213/3
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A well known property of the {gamma}-ray sources detected by Cos-B in the 1970s, by the Compton Gamma-Ray Observatory in the 1990s, and recently by the Fermi observations is the presence of radio counterparts, particularly for those associated with extragalactic objects. This observational evidence is the basis of the radio-{gamma}-ray connection established for the class of active galactic nuclei known as blazars. In particular, the main spectral property of the radio counterparts associated with {gamma}-ray blazars is that they show a flat spectrum in the GHz frequency range. Our recent analysis dedicated to search blazar-like candidates as potential counterparts for the unidentified {gamma}-ray sources allowed us to extend the radio-{gamma}-ray connection in the MHz regime. We also showed that blazars below 1GHz maintain flat radio spectra. Thus, on the basis of these new results, we assembled a low-frequency radio catalog of flat-spectrum sources built by combining the radio observations of the Westerbork Northern Sky Survey and of the Westerbork in the southern hemisphere catalog with those of the NRAO Very Large Array Sky survey (NVSS). This could be used in the future to search for new, unknown blazar-like counterparts of {gamma}-ray sources. First, we found NVSS counterparts of Westerbork Synthesis Radio Telescope radio sources, and then we selected flat-spectrum radio sources according to a new spectral criterion, specifically defined for radio observations performed below 1GHz. We also described the main properties of the catalog listing 28358 radio sources and their logN-logS distributions. Finally, a comparison with the Green Bank 6cm radio source catalog was performed to investigate the spectral shape of the low-frequency flat-spectrum radio sources at higher frequencies.
- ID:
- ivo://CDS.VizieR/J/MNRAS/440/799
- Title:
- Low Ionization BALQSOs MgII and AlIII variability
- Short Name:
- J/MNRAS/440/799
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results of our time variability studies of MgII and AlIII absorption lines in a sample of 22 Low Ionization Broad Absorption Line QSOs (LoBAL QSOs) at 0.2<=z_em_<=2.1 using the 2-m telescope at IUCAA Girawali Observatory over a time-scale of 10d to 7.69years in the QSO's rest frame. Spectra are analysed in conjunction with photometric light curves from Catalina Real-Time Transient Survey. Long time-scale (i.e. >=1-year) absorption line variability is seen in eight cases (36 per cent systems) while only four of them (i.e. 18 per cent systems) show variability over short time-scales (i.e. <1-year). We notice a tendency of highly variable LoBAL QSOs to have high ejection velocity, low equivalent width and low redshift. The detection rate of variability in LoBAL QSOs showing Fe fine-structure lines (FeLoBAL QSOs) is less than that seen in non-Fe LoBAL QSOs. Absorption line variability is more frequently detected in QSOs having continuum dominated by Fe emission lines compared to rest of the QSOs. Confirming these trends with a bigger sample will give vital clues for understanding the physical distinction between different BAL QSO sub-classes. We correlate the absorption line variability with various parameters derived from continuum light curves and find no clear correlation between continuum flux and absorption line variabilities. However, sources with large absorption line variability also show large variability in their light curves. We also see appearance/disappearance of absorption components in two cases and clear indications for profile variations in four cases. The observed variability can be best explained by a combination of process driven by continuum variations and clouds transiting across the line of sight.
- ID:
- ivo://CDS.VizieR/J/A+A/561/A140
- Title:
- Low-luminosity type-1 QSO sample
- Short Name:
- J/A+A/561/A140
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recognizing the properties of the host galaxies of quasi-stellar objects (QSOs) is essential to understand the suspected coevolution of central supermassive black holes (BHs) and their host galaxies. We selected a subsample of the Hamburg/ESO survey for bright UV-excess QSOs, containing only the 99 nearest QSOs with redshift z<=0.06, that are close enough to allow detailed structural analysis. From this "low-luminosity type-1 QSO sample", we observed 20 galaxies and performed aperture photometry and bulge-disk-bar-AGN-decomposition with BUDDA on near-infrared J, H, K band images. From the photometric decomposition of these 20 objects and visual inspection of images of another 26, we find that ~50% of the hosts are disk galaxies and most of them (86%) are barred. Stellar masses, calculated from parametric models based on inactive galaxy colors, range from 2x10^9^M_{sun}_ to 2x10^11^M_{sun}_. Black hole masses measured from single epoch spectroscopy range from 1x10^6^M_{sun}_ to 5x10^8^M_{sun}_. In comparison to higher luminosity QSO samples, LLQSOs tend to have lower stellar and BH masses. Also, in the effective radius vs. mean surface-brightness projection of the fundamental plane, they lie in the transition area between luminous QSOs and "normal" galaxies. This can be seen as further evidence that they can be pictured as a "bridge" between the local Seyfert population and luminous QSOs at higher redshift. Eleven low-luminosity QSOs for which we have reliable morphological decompositions and BH mass estimations lie below the published BH mass vs. bulge luminosity relations for inactive galaxies. This could be partially explained by bulges of active galaxies containing much younger stellar populations than bulges of inactive galaxies. Also, one could suspect that their BHs are undermassive. This might hint at the growth of the host spheroid to precede that of the BH.
- ID:
- ivo://CDS.VizieR/J/MNRAS/441/1802
- Title:
- Low-redshift QSOs in SDSS Stripe 82
- Short Name:
- J/MNRAS/441/1802
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the environments of low-redshift (z<0.5) quasars based on a large and homogeneous data set from the Stripe 82 region of the Sloan Digital Sky Survey (SDSS). We have compared the <1Mpc scale environments of 302 quasars that were resolved in our recent study to those of 288 inactive galaxies with closely matched redshifts. Crucially, the luminosities of the inactive galaxies and the quasar host galaxies are also closely matched, unlike in most previous studies. The environmental overdensities were studied by measuring the number density of galaxies within a projected distance of 200kpc to 1Mpc. The galaxy number density of the quasar environments is comparable to that of the inactive galaxies with similar luminosities, both classes of objects showing significant excess compared to the background galaxy density for distances <400kpc. There is no significant dependence of the galaxy number density on redshift, quasar or host galaxy luminosity, black hole mass or radio loudness. This suggests that the fuelling and triggering of the nuclear activity is only weakly dependent on the local environment of quasars, and the quasar phase may be a short-lived common phase in the life cycle of all massive galaxies.
