- ID:
- ivo://CDS.VizieR/J/AJ/144/49
- Title:
- Quasars from SDSS-DR7, WISE and UKIDSS surveys
- Short Name:
- J/AJ/144/49
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of 37842 quasars in the Sloan Digital Sky Survey (SDSS) Data Release 7, which have counterparts within 6" in the Wide-field Infrared Survey Explorer (WISE) Preliminary Data Release. The overall WISE detection rate of the SDSS quasars is 86.7%, and it decreases to less than 50.0% when the quasar magnitude is fainter than i=20.5. We derive the median color-redshift relations based on this SDSS-WISE quasar sample and apply them to estimate the photometric redshifts of the SDSS-WISE quasars. We find that by adding the WISE W1- and W2-band data to the SDSS photometry we can increase the photometric redshift reliability, defined as the percentage of sources with photometric and spectroscopic redshift difference less than 0.2, from 70.3% to 77.2%. We also obtain the samples of WISE-detected normal and late-type stars with SDSS spectroscopy, and present a criterion in the z-W1 versus g-z color-color diagram, z-W1>0.66(g-z)+2.01, to separate quasars from stars. With this criterion we can recover 98.6% of 3089 radio-detected SDSS-WISE quasars with redshifts less than four and overcome the difficulty in selecting quasars with redshifts between 2.2 and 3 from SDSS photometric data alone. We also suggest another criterion involving the WISE color only, W1-W2>0.57, to efficiently separate quasars with redshifts less than 3.2 from stars. In addition, we compile a catalog of 5614 SDSS quasars detected by both WISE and UKIDSS surveys and present their color-redshift relations in the optical and infrared bands. By using the SDSS ugriz, UKIDSS, YJHK, and WISE W1- and W2-band photometric data, we can efficiently select quasar candidates and increase the photometric redshift reliability up to 87.0%. We discuss the implications of our results on the future quasar surveys. An updated SDSS-WISE quasar catalog consisting of 101853 quasars with the recently released WISE all-sky data is also provided.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/266/317
- Title:
- Quasars in ESO/SERC field 927
- Short Name:
- J/MNRAS/266/317
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the spectroscopic observations of 56 quasars that were discovered by AQD (Automated Quasar Detection) in a field of ~25.3deg2, centred at (1950) RA l0h40m00s, Dec. 05deg00'00". These observations, with the CTIO 4-m telescope, led to the discovery by Clowes & Campusano of a large group of quasars with size ~100-200h^-1^Mpc at z~1.3. Quasars of particular interest are noted, including one that is a BAL quasar with z~1.78.
- ID:
- ivo://CDS.VizieR/J/AJ/123/578
- Title:
- Quasars in the Coma cluster
- Short Name:
- J/AJ/123/578
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This is the second paper of the series about our Multiwavelength Quasar Survey. We present the observational results for the X-ray candidates in the field of the Coma Cluster. Nine new X-ray active galactic nuclei are discovered.
- ID:
- ivo://CDS.VizieR/J/MNRAS/450/3904
- Title:
- Quasars narrow absorption lines from SDSS
- Short Name:
- J/MNRAS/450/3904
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We assemble 3524 quasars from the Sloan Digital Sky Survey (SDSS) with repeated observations to search for variations of the narrow C IV {lambda}{lambda}1548, 1551 and Mg II {lambda}{lambda}2796, 2803 absorption doublets in spectral regions shortward of 7000{AA} in the observed frame, which corresponds to time-scales of about 150-2643d in the quasar rest frame. In these quasar spectra, we detect 3580 CIV absorption systems with z_abs_=1.5188-3.5212 and 1809 MgII absorption systems with z_abs_=0.3948-1.7167. In term of the absorber velocity ({beta}) distribution in the quasar rest frame, we find a substantial number of CIV absorbers with {beta}<0.06, which might be connected to absorption of quasar outflows. The outflow absorption peaks at {upsilon}~2000km/s and drops rapidly below this peak value. Among 3580 CIV absorption systems, 52 systems (~1.5 percent) show obvious variations in equivalent widths in the absorber rest frame (W_r_): 16 enhanced, 16 emerged, 12 weakened and 8 disappeared systems, respectively. We find that changes in W_r_{lambda}1548 are related neither to the time-scales of the two SDSS observations nor to absorber velocities in the quasar rest frame. Variable absorption in low-ionization species is important to constrain the physical conditions of the absorbing gas. There are two variable MgII absorption systems measured from SDSS spectra detected by Hacker et al. (2013, J/MNRAS/434/163). However, in our MgII absorption sample, we find that neither shows variable absorption with confident levels of >4{sigma} for {lambda}2796 lines and >3{sigma} for {lambda}2803 lines.
- ID:
- ivo://CDS.VizieR/J/MNRAS/468/L6
- Title:
- Quasars narrow absorption lines from SDSS
- Short Name:
- J/MNRAS/468/L6
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this Letter, we report the discovery of a strong correlation between the variability of narrow absorption lines (NALs) and the ionizing continuum from a two-epoch spectral sample of 40 quasars containing 52 variable CIV {lambda}{lambda}1548, 1551 absorption doublets. According to the concordance index, this sample is classified into two subsamples. Subsample I shows an anti-correlation between the variations of absorption lines and the continuum, while Subsample II exhibits a positive correlation. These results imply that these variable CIV {lambda}{lambda}1548, 1551 absorption doublets are intrinsic to the corresponding quasars and that their variations are caused primarily by the fluctuations of the ionizing continuum. Based on our analysis, we propose that there might be two kinds of absorption gas: one that is very sensitive to the continuum variations, and another that is not. In addition, we suggest that in many cases the emergence or disappearance of NALs is caused by fluctuations of the ionizing continuum.
- ID:
- ivo://CDS.VizieR/J/ApJ/801/45
- Title:
- Quasars properties and reverberation mapping
- Short Name:
- J/ApJ/801/45
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We explore the practical feasibility of active galactic nucleus (AGN) broadband reverberation mapping and present first results. We lay out and apply a rigorous approach for the stochastic reverberation mapping of unevenly sampled multi-broadband flux measurements, assuming that the broad-line region (BLR) line flux is contributing up to 15% in some bands, and is directly constrained by one spectroscopical epoch. The approach describes variations of the observed flux as the continuum, modeled as a stochastic Gaussian process, and emission line contribution, modeled as a scaled, smoothed, and delayed version of the continuum. This approach can be used not only to interpolate in time between measurements, but also to determine confidence limits on continuum-line emission delays. This approach is applied to Sloan Digital Sky Survey observations in Stripe 82 (S82), providing flux measurements that are precise to 2% at ~60 epochs over ~10 yr. The strong annual variations in the epoch sampling prove a serious limitation in practice. In addition, suitable redshift ranges must be identified where strong, broad emission lines contribute to one filter, but not to another. By generating and evaluating problem-specific mock data, we verify that S82-like data can constrain {tau}_delay_ for a simple transfer function model. In application to real data, we estimate {tau}_delay_ for 323 AGNs with 0.225<z<0.846, combining information for different objects through the ensemble-scaling relationships for BLR size and black hole mass. Our analysis tentatively indicates a 1.7 times larger BLR size of H{alpha} and Mg II compared to Kaspi et al. (2000ApJ...533..631K; 2007ApJ...659..997K) and Vestergaard (2002ApJ...571..733V; 2006ApJ...641..689V), but the seasonal data sampling casts doubt on the robustness of the inference.
- ID:
- ivo://CDS.VizieR/J/ApJ/679/962
- Title:
- Quasars with strong nitrogen emission lines
- Short Name:
- J/ApJ/679/962
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on 293 quasars with strong NIV] {lambda}1486 or NIII] {lambda}1750 emission lines (rest-frame equivalent width >3{AA}) at 1.7<z<4.0 selected from the Sloan Digital Sky Survey (SDSS) Fifth Data Release (Cat. VII/252). These nitrogen-rich (N-rich) objects comprise ~1.1% of the SDSS quasars. The comparison between the N-rich quasars and other quasars shows that the two quasar subsets share many common properties. We also confirm previous results that N-rich quasars have much stronger Ly{alpha} and NV {lambda}1240 emission lines. Strong nitrogen emission in all ionization states indicates high overall nitrogen abundances in these objects. We find evidence that the nitrogen abundance is closely related to quasar radio properties.
698. Quasar variability
- ID:
- ivo://CDS.VizieR/J/A+AS/143/465
- Title:
- Quasar variability
- Short Name:
- J/A+AS/143/465
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The relation between quasar variability and parameters such as luminosity and redshift has been a matter of hot debate over the last few years with many papers on the subject. Any correlations which can be established will have a profound effect on models of quasar structure and evolution. The sample of quasars with redshifts in ESO/SERC field 287 contains over 600 quasars in the range 0<z<3.5 and is now large enough to bin in luminosity and redshift, and give definitive measures of the correlations. We find no significant correlation between amplitude and redshift, except perhaps at very low redshift, but an inverse correlation between amplitude and luminosity. This is examined in the context of various models for quasar variability.
699. Quasar variability
- ID:
- ivo://CDS.VizieR/J/MNRAS/375/989
- Title:
- Quasar variability
- Short Name:
- J/MNRAS/375/989
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In order to investigate the dependence of quasar variability on fundamental physical parameters like black hole mass, we have matched quasars from the Quasar Equatorial Survey Team, Phase 1 (QUEST1) variability survey with broad-lined objects from the Sloan Digital Sky Survey. The matched sample contains 104 quasars, and the Sloan spectra are used to estimate black hole masses and bolometric luminosities. Variability amplitudes are measured from the QUEST1 light curves. We find that black hole mass correlates with several measures of the variability amplitude at the 99 per cent significance level or better. The correlation does not appear to be caused by obvious selection effects inherent to flux-limited quasar samples, host galaxy contamination or other well-known correlations between quasar variability and luminosity/redshift. We evaluate variability as a function of rest-frame time lag using structure functions and find further support for the variability-black hole mass correlation.
- ID:
- ivo://CDS.VizieR/J/ApJ/753/106
- Title:
- Quasar variability with SDSS and POSS imaging
- Short Name:
- J/ApJ/753/106
- Date:
- 11 Mar 2022 15:31:25
- Publisher:
- CDS
- Description:
- We provide a quantitative description and statistical interpretation of the optical continuum variability of quasars. The Sloan Digital Sky Survey (SDSS) has obtained repeated imaging in five UV-to-IR photometric bands for 33,881 spectroscopically confirmed quasars. About 10,000 quasars have an average of 60 observations in each band obtained over a decade along Stripe 82 (S82), whereas the remaining ~25,000 have 2-3 observations due to scan overlaps. The observed time lags span the range from a day to almost 10 years, and constrain quasar variability at rest-frame time lags of up to 4 years, and at rest-frame wavelengths from 1000{AA} to 6000{AA}. We publicly release a user-friendly catalog of quasars from the SDSS Data Release 7 that have been observed at least twice in SDSS or once in both SDSS and the Palomar Observatory Sky Survey, and we use it to analyze the ensemble properties of quasar variability. Based on a damped random walk (DRW) model defined by a characteristic timescale and an asymptotic variability amplitude that scale with the luminosity, black hole mass, and rest wavelength for individual quasars calibrated in S82, we can fully explain the ensemble variability statistics of the non-S82 quasars such as the exponential distribution of large magnitude changes. All available data are consistent with the DRW model as a viable description of the optical continuum variability of quasars on timescales of ~5-2000 days in the rest frame. We use these models to predict the incidence of quasar contamination in transient surveys such as those from the Palomar Transient Factory and Large Synoptic Survey Telescope.
