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Start Over Subject quasars Capability Type Table Access Protocol
591. Parkes Quarter-Jansky Flat-Spectrum Sample. II.
ID:
ivo://CDS.VizieR/J/A+A/399/469
Title:
Parkes Quarter-Jansky Flat-Spectrum Sample. II.
Short Name:
J/A+A/399/469
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present optical spectra and redshift measurements for 178 flat-spectrum objects from the Parkes quarter-Jansky flat-spectrum sample. These spectra were obtained in order to compile a complete sample of quasars for use in a study of quasar evolution. We present a composite optical spectrum made from the subset of 109 quasars that have flux densities in the range 0.25Jy<S(2.7GHz)<0.5Jy, and make a comparison with a composite spectrum for radio-quiet QSOs from the Large Bright Quasar Survey. Our large sample of radio-loud quasars allows us to strengthen previous reports that the Ly and CIV emission lines have larger equivalent width in radio-loud quasars than radio-quiet QSOs to greater than the 3{sigma} level. However we see no significant difference in the equivalent widths of CIII] or MgII. We also show that the flux decrements across the Lyman-{alpha} line (DA) measured from these spectra show the same trend with redshift as for optically selected QSOs.
592. PG 2130+099 narrowband light curves
ID:
ivo://CDS.VizieR/J/A+A/659/A13
Title:
PG 2130+099 narrowband light curves
Short Name:
J/A+A/659/A13
Date:
25 Feb 2022 07:32:33
Publisher:
CDS
Description:
We present the results of an intensive six-month optical continuum reverberation mapping campaign of the Seyfert 1 galaxy PG 2130+099 at redshift z=0.063. The ground- based photometric monitoring was conducted on a daily basis with the robotic 46cm telescope of the Wise observatory located in Israel. Specially designed narrowband filters were used to observe the central engine of the active galactic nucleus (AGN), avoiding line contamination from the broad-line region (BLR). We aim to measure inter- band continuum time lags across the optical range and determine the size-wavelength relation for this system. PG 2130+099 displays correlated variability across the optical range, and we successfully detect significant time lags of up to 3 days between the multiband light curves. While a continuum reprocessing model can fit the data reasonably well, our derived disk sizes are a factor of 2-6 larger than the theoretical disk sizes predicted from the AGN luminosity estimate of PG 2130+099. This result is in agreement with previous studies of AGN/quasars and suggests that the standard Shakura- Sunyaev disk theory has limitations in describing AGN accretion disks.
593. Photometric Classification Catalogue of SDSS DR7
ID:
ivo://CDS.VizieR/J/MNRAS/419/80
Title:
Photometric Classification Catalogue of SDSS DR7
Short Name:
J/MNRAS/419/80
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a catalogue of about six million unresolved photometric detections in the Sloan Digital Sky Survey (SDSS) Seventh Data Release, classifying them into stars, galaxies and quasars. We use a machine learning classifier trained on a subset of spectroscopically confirmed objects from 14th to 22nd magnitude in the SDSS i band. Our catalogue consists of 2430625 quasars, 3544036 stars and 63586 unresolved galaxies from 14th to 24th magnitude in the SDSS i-band. Our algorithm recovers 99.96 per cent of spectroscopically confirmed quasars and 99.51 per cent of stars to i~21.3 in the colour window that we study. The level of contamination due to data artefacts for objects beyond i=21.3 is highly uncertain and all mention of completeness and contamination in the paper are valid only for objects brighter than this magnitude. However, a comparison of the predicted number of quasars with the theoretical number counts shows reasonable agreement.
594. Photometric classification of QSO from RCS-2
ID:
ivo://CDS.VizieR/J/A+A/584/A44
Title:
Photometric classification of QSO from RCS-2
Short Name:
J/A+A/584/A44
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present new quasar candidate catalogs from the Red-Sequence Cluster Survey 2 (RCS-2), identified solely from photometric information using a Random Forest algorithm. The algorithm is trained using a well-defined SDSS spectroscopic sample of quasars and stars. The algorithm identifies putative quasars from broadband magnitudes (g, r, i, z) and colors. Exploiting NUV GALEX measurements for a subset of the objects, we refine the classifier by adding new information. An additional subset of the data with WISE W1 and W2 bands is also studied. Upon analyzing 542,897 RCS-2 point sources, the algorithm identified 21,501 quasar candidates, with a training-set-derived precision of 89.5% and recall of 88.4%. These performance metrics improve for the GALEX subset; 6530 quasar candidates are identified from 16898 sources, with a precision and recall respectively of 97.0% and 97.5%. Algorithm performance is further improved when WISE data are included, with precision and recall increasing to 99.3% and 99.1% respectively for 21834 quasar candidates from 242902 sources. After merging these samples and removing duplicates, we obtain 38257 candidates.
595. Photometric quasar candidates in Stripe 82
ID:
ivo://CDS.VizieR/J/A+A/611/A97
Title:
Photometric quasar candidates in Stripe 82
Short Name:
J/A+A/611/A97
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have applied a convolutional neural network (CNN) to classify and detect quasars in the Sloan Digital Sky Survey Stripe 82 and also to predict the photometric redshifts of quasars. The network takes the variability of objects into account by converting light curves into images. The width of the images, noted w, corresponds to the five magnitudes ugriz and the height of the images, noted h, represents the date of the observation. The CNN provides good results since its precision is 0.988 for a recall of 0.90, compared to a precision of 0.985 for the same recall with a random forest classifier. Moreover 175 new quasar candidates are found with the CNN considering a fixed recall of 0.97. The combination of probabilities given by the CNN and the random forest makes good performance even better with a precision of 0.99 for a recall of 0.90. For the redshift predictions, the CNN presents excellent results which are higher than those obtained with a feature extraction step and different classifiers (a K-nearest-neighbors, a support vector machine, a random forest and a Gaussian process classifier). Indeed, the accuracy of the CNN within |{DELTA}z|<0.1 can reach 78.09%, within |{DELTA}z|<0.2 reaches 86.15%, within |{DELTA}z|<0.3 reaches 91.2% and the value of root mean square (rms) is 0.359. The performance of the KNN decreases for the three |{DELTA}z| regions, since within the accuracy of |{DELTA}z|<0.1, |{DELTA}z|<0.2, and |{DELTA}z|<0.3 is 73.72%, 82.46%, and 90.09% respectively, and the value of rms amounts to 0.395. So the CNN successfully reduces the dispersion and the catastrophic redshifts of quasars. This new method is very promising for the future of big databases such as the Large Synoptic Survey Telescope.
596. Photometric redshifts of X-ray sources in CDF-S
ID:
ivo://CDS.VizieR/J/ApJS/155/73
Title:
Photometric redshifts of X-ray sources in CDF-S
Short Name:
J/ApJS/155/73
Date:
21 Oct 2021
Publisher:
CDS
Description:
Based on the photometry of 10 near-ultraviolet, optical, and near-infrared bands of the Chandra Deep Field-South, we estimate the photometric redshifts for 342 X-ray sources, which constitute ~99% of all the detected X-ray sources in the field.
597. Photometric selection of quasars from SDSS. II.
ID:
ivo://CDS.VizieR/J/ApJS/180/67
Title:
Photometric selection of quasars from SDSS. II.
Short Name:
J/ApJS/180/67
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a catalog of 1172157 quasar candidates selected from the photometric imaging data of the Sloan Digital Sky Survey (SDSS). The objects are all point sources to a limiting magnitude of i=21.3 from 8417deg^2^ of imaging from SDSS Data Release 6 (DR6). This sample extends our previous catalog by using the latest SDSS public release data and probing both ultraviolet (UV)-excess and high-redshift quasars. While the addition of high-redshift candidates reduces the overall efficiency (quasars:quasar candidates) of the catalog to ~80%, it is expected to contain no fewer than 850000 bona fide quasars, which is ~8 times the number of our previous sample and ~10 times the size of the largest spectroscopic quasar catalog. Cross-matching between our photometric catalog and spectroscopic quasar catalogs from both the SDSS and 2dF survey yields 88879 spectroscopically confirmed quasars. For judicious selection of the most robust UV-excess sources (~500000 objects in all), the efficiency is nearly 97% -more than sufficient for detailed statistical analyses. The catalog's completeness to type 1 (broad-line) quasars is expected to be no worse than 70%, with most missing objects occurring at z<0.7 and 2.5<z<3.0. In addition to classification information, we provide photometric redshift estimates (typically good to {Delta}z+/-0.3[2{sigma}]) and cross-matching with radio, X-ray, and proper-motion catalogs. Finally, we consider the catalog's utility for determining the optical luminosity function of quasars and are able to confirm the flattening of the bright-end slope of the quasar luminosity function at z~4 as compared to z~2.
598. Photometric standards around gravitational lenses
ID:
ivo://CDS.VizieR/J/A+A/402/1157
Title:
Photometric standards around gravitational lenses
Short Name:
J/A+A/402/1157
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a catalog of secondary photometric standard stars in the neighborhood of 14 gravitationally lensed quasars. These stars were verified to be non variable using long-term monitoring. The instrumental magnitudes of the new standard stars have been transformed to the Johnson-Cousins BV(RI)c photometric system. For ten gravitational lenses (GLs) we also provide the BV(RI)c mean magnitudes of the integrated flux of all the lens components, for the epochs of the photometric calibration.
599. Physical conditions of high redshift DLAs
ID:
ivo://CDS.VizieR/J/ApJ/800/7
Title:
Physical conditions of high redshift DLAs
Short Name:
J/ApJ/800/7
Date:
21 Oct 2021
Publisher:
CDS
Description:
A new method is used to measure the physical conditions of the gas in damped Ly{alpha} systems (DLAs). Using high-resolution absorption spectra of a sample of 80 DLAs, we are able to measure the ratio of the upper and lower fine-structure levels of the ground state of C^+^ and Si^+^. These ratios are determined solely by the physical conditions of the gas. We explore the allowed physical parameter space using a Monte Carlo Markov chain method to constrain simultaneously the temperature, neutral hydrogen density, and electron density of each DLA. The results indicate that at least 5% of all DLAs have the bulk of their gas in a dense, cold phase with typical densities of ~100/cm3 and temperatures below 500K. We further find that the typical pressure of DLAs in our sample is log(P/k_B_)=3.4(K/cm3), which is comparable to the pressure of the local interstellar medium (ISM), and that the components containing the bulk of the neutral gas can be quite small with absorption sizes as small as a few parsecs. We show that the majority of the systems are consistent with having densities significantly higher than expected for a purely canonical warm neutral medium, indicating that significant quantities of dense gas (i.e., n_H_>0.1/cm3) are required to match observations. Finally, we identify eight systems with positive detections of Si II*. These systems have pressures (P/k_B_) in excess of 20000K/cm3, which suggest that these systems tag a highly turbulent ISM in young, star-forming galaxies.
600. Physical parameters of ~300000 SDSS-DR12 QSOs
ID:
ivo://CDS.VizieR/J/ApJS/228/9
Title:
Physical parameters of ~300000 SDSS-DR12 QSOs
Short Name:
J/ApJS/228/9
Date:
21 Oct 2021
Publisher:
CDS
Description:
We use the Sloan Digital Sky Survey (SDSS) Quasar Data Release 12 (DR12Q), containing nearly 300000 active galactic nuclei (AGNs), to calculate the monochromatic luminosities at 5100, 3000, and 1350{AA}, derived from the broadband extinction-corrected SDSS magnitudes. After matching these sources to their counterparts from the SDSS Quasar Data Release 7 (DR7Q), we find very high correlations between our luminosities and DR7Q spectra-based luminosities with minute mean offsets (~0.01dex) and dispersions of differences of 0.11, 0.10, and 0.12dex, respectively, across a luminosity range of 2.5dex. We then estimate the black hole (BH) masses of the AGNs using the broad line region radius-disk luminosity relations and the FWHM of the MgII and CIV emission lines, to provide a catalog of 283033 virial BH mass estimates (132451 for MgII, 213071 for CIV, and 62489 for both) along with the estimates of the bolometric luminosity and Eddington ratio for 0.1<z<5.5 and for roughly a quarter of the sky covered by SDSS. The BH mass estimates from Mg II turned out to be closely matched to the ones from DR7Q with a dispersion of differences of 0.34dex across a BH mass range of ~2dex. We uncovered a bias in the derived CIV FWHMs from DR12Q as compared to DR7Q, which we correct empirically. The CIV BH mass estimates should be used with caution because the CIV line is known to cause problems in the estimation of BH mass from single-epoch spectra. Finally, after the FWHM correction, the AGN BH mass estimates from CIV closely match the DR7Q ones (with a dispersion of 0.28dex), and more importantly the MgII and CIV BH masses agree internally with a mean offset of 0.07dex and a dispersion of 0.39dex.