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811. SDSS J120414.37+351800.5 quasar optical photometry
ID:
ivo://CDS.VizieR/J/ApJ/859/8
Title:
SDSS J120414.37+351800.5 quasar optical photometry
Short Name:
J/ApJ/859/8
Date:
21 Oct 2021
Publisher:
CDS
Description:
A small fraction of quasars show an unusually high nitrogen-to-carbon ratio (N/C) in their spectra. These "nitrogen-rich" (N-rich) quasars are a long-standing puzzle because their interstellar medium implies stellar populations with abnormally high metallicities. It has recently been proposed that N-rich quasars may result from tidal disruption events (TDEs) of stars by supermassive black holes. The rapid enhancement of nitrogen and the depletion of carbon due to the carbon-nitrogen-oxygen cycle in supersolar mass stars could naturally produce high N/C. However, the TDE hypothesis predicts that the N/C should change with time, which has never hitherto been observed. Here we report the discovery of the first N-rich quasar with rapid N/C variability that could be caused by a TDE. Two spectra separated by 1.7yrs (rest-frame) show that the NIII]{lambda}1750/CIII]{lambda}1909 intensity ratio decayed by ~86%+/-14% (1{sigma}). Optical (rest-frame UV) light-curve and X-ray observations are qualitatively consistent with the TDE hypothesis; though, the time baseline falls short of a definitive proof. Putting the single-object discovery into context, statistical analyses of the ~80 known N-rich quasars with high-quality archival spectra show evidence (at a 5{sigma} significance level) of a decrease in N/C on timescales of >1 year (rest-frame) and a constant level of ionization (indicated by the CIII]{lambda}1909/CIV{lambda}1549 intensity ratio). If confirmed, our results demonstrate the method of identifying TDE candidates in quasars via abundance ratio variability, opening a new window of TDE observations at high redshift (z>2) with upcoming large-scale time-domain spectroscopic surveys.
812. SDSS J1004+4112 spectra
ID:
ivo://CDS.VizieR/J/A+A/634/A27
Title:
SDSS J1004+4112 spectra
Short Name:
J/A+A/634/A27
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present new spectroscopic and polarimetric observations of the gravitational lens SDSS J1004+4112 taken with the 6m telescope of the Special Astrophysical Observatory (SAO, Russia). In order to explain the variability that is observed only in the blue wing of the CIV emission line, corresponding to image A, we analyze the spectroscopy and polarimetry of the four images of the lensed system. Spectra of the four images were taken in 2007, 2008, and 2018, and polarization was measured in the period 2014-2017. Additionally, we modeled the microlensing effect in the polarized light, assuming that the source of polarization is the equatorial scattering in the inner part of the torus. We find that a blue enhancement in the CIV line wings affects component A in all three epochs. We also find that the UV continuum of component D was amplified in the period 2007-2008, and that the red wings of CIII] and CIV appear brighter in D than in the other three components. We report significant changes in the polarization parameters of image D, which can be explained by microlensing. Our simulations of microlensing of an equatorial scattering region in the dusty torus can qualitatively explain the observed changes in the polarization degree and angle of image D.We do not detect significant variability in the polarization parameters of the other images (A, B, and C), although the averaged values of the polarization degree and angle are different for the different images. Microlensing of a broad line region model including a compact outflowing component can qualitatively explain the CIV blue wing enhancement (and variation) in component A. However, to confirmed this hypothesis, we need additional spectroscopic observation in future.
813. SDSS J1339+1310 spectra and light curves
ID:
ivo://CDS.VizieR/J/A+A/596/A77
Title:
SDSS J1339+1310 spectra and light curves
Short Name:
J/A+A/596/A77
Date:
21 Oct 2021
Publisher:
CDS
Description:
We spectroscopically re-observed the gravitational lens system SDSS J1339+1310 using OSIRIS on the GTC. We also monitored the r-band variability of the two quasar images (A and B) with the LT over 143 epochs in the period 2009-2016. These new data in both the wavelength and time domains have confirmed that the system is an unusual microlensing factory. The CIV emission line is remarkably microlensed, since the microlensing magnification of B relative to that for A,{mu}_BA_, reaches a value of 1.4 (~0.4mag) for its core. Moreover, the B image shows a red wing enhancement of CIV flux (relative to A), and {mu}_BA_=2 (0.75mag) for the CIV broad-line emission. Regarding the nuclear continuum, we find a chromatic behaviour of {mu}_BA_, which roughly varies from ~5 (1.75mag) at 7000{AA} to ~6 (1.95mag) at 4000{AA}. We also detect significant microlensing variability in the r band, and this includes a number of microlensing events on timescales of 50-100d. Fortunately, the presence of an intrinsic 0.7 mag dip in the light curves of A and B, permitted us to measure the time delay between both quasar images. This delay is {Delta}t_AB_=47^+5^_-6_d (1{sigma} confidence interval; A is leading), in good agreement with predictions of lens models.
814. SDSS J081830.46+060138.0 spectropolarimetry
ID:
ivo://CDS.VizieR/J/A+A/633/A101
Title:
SDSS J081830.46+060138.0 spectropolarimetry
Short Name:
J/A+A/633/A101
Date:
21 Oct 2021
Publisher:
CDS
Description:
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.
815. SDSS J151349.52+035211.28 Xshooter spectra
ID:
ivo://CDS.VizieR/J/A+A/618/A184
Title:
SDSS J151349.52+035211.28 Xshooter spectra
Short Name:
J/A+A/618/A184
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the detection and detailed analysis of a diffuse molecular cloud at z_abs_=2.4636 towards the quasar SDSS J151349.52+035211.28 (hereafter J1513+0352) (zem~=2.68) observed with the X-shooter spectrograph at the Very Large Telescope. We measure very high column densities of atomic and molecular hydrogen, with logN(HI,H_2_)~=21.8,21.3. This is the highest H_2_ column density ever measured in an intervening damped Lyman-{alpha}system but we do not detect CO, implying log N(CO)/N(H_2_)<-7.8, which could be due to a low metallicity of the cloud. From the metal absorption lines, we derive the metallicity to be Z~=0.15Z_{sun}_ and determine the amount of dust by measuring the induced extinction of the background quasar light, AV~=0.4. We simultaneously detect Ly{alpha} emission at the same redshift, with a centroid located at a most probable impact parameter of only {rho}~=1.4kpc. We argue that the line of sight is therefore likely passing through the interstellar medium of a galaxy, as opposed to the circumgalactic medium. The relation between the surface density of gas and that of star formation seems to follow the global empirical relation derived in the nearby Universe although our constraints on the star formation rate and on the galaxy extent remain too loose to be conclusive. We study the transition from atomic to molecular hydrogen using a theoretical description based on the microphysics of molecular hydrogen.We use the derived chemical properties of the cloud and physical conditions (Tk~=90K and n~=250cm^-3^) derived through the excitation of H_2_ rotational levels and neutral carbon fine structure transitions to constrain the fundamental parameters that govern this transition. By comparing the theoretical and observed HI column densities, we are able to bring an independent constraint on the incident UV flux, which we find to be in agreement with that estimated from the observed star formation rate.
816. SDSS Lyman limit systems at z~3.5
ID:
ivo://CDS.VizieR/J/ApJ/718/392
Title:
SDSS Lyman limit systems at z~3.5
Short Name:
J/ApJ/718/392
Date:
21 Oct 2021
Publisher:
CDS
Description:
We perform a semi-automated survey for {tau}_912_>=2 Lyman limit systems (LLSs) in quasar spectra from the Sloan Digital Sky Survey, Data Release 7. From a starting sample of 2473 quasars with z_em_=3.6-5.0, we analyze 429 spectra meeting strict selection criteria for a total redshift path {Delta}z=93.8 and identify 190 intervening systems at z_LLS_>=3.3. We also perform a survey for proximate LLSs (PLLSs) and find that {l}_PLLS_(z) is systematically lower (~25%) than intervening systems.
817. SDSS & MMT obs. of extremely massive QSOs & gal.
ID:
ivo://CDS.VizieR/J/ApJ/871/57
Title:
SDSS & MMT obs. of extremely massive QSOs & gal.
Short Name:
J/ApJ/871/57
Date:
21 Oct 2021
Publisher:
CDS
Description:
Black hole mass scaling relations suggest that extremely massive black holes (EMBHs) with M_BH_>~10^9.4^M_{sun}_ are found in the most massive galaxies with M_star_>~10^11.6^M_{sun}_, which are commonly found in dense environments, like galaxy clusters. Therefore, one can expect that there is a close connection between active EMBHs and dense environments. Here, we study the environments of 9461 galaxies and 2943 quasars at 0.24<~z<~0.40, among which 52 are extremely massive quasars with log(M_BH_/M_{sun}_)>=~9.4, using Sloan Digital Sky Survey and MMT Hectospec data. We find that, on average, both massive quasars and massive galaxies reside in environments more than ~2 times as dense as those of their less massive counterparts with log(M_BH_/M_{sun}_)<~9.0. However, massive quasars reside in environments about ~2 times less dense than inactive galaxies with log(M_BH_/M_{sun}_)>=9.4, and only about one third of massive quasars are found in galaxy clusters, while about two thirds of massive galaxies reside in such clusters. This indicates that massive galaxies are a much better signpost for galaxy clusters than massive quasars. The prevalence of massive quasars in moderate to low density environments is puzzling, considering that several simulation results show that these quasars appear to prefer dense environments. Several possible reasons for this discrepancy are discussed, although further investigation is needed to obtain a definite explanation.
818. SDSS QSO DR7 and DR9
ID:
ivo://CDS.VizieR/J/A+A/616/A97
Title:
SDSS QSO DR7 and DR9
Short Name:
J/A+A/616/A97
Date:
21 Oct 2021
Publisher:
CDS
Description:
The explosion of data in recent years has generated an increasing need for new analysis techniques in order to extract knowledge from massive data-sets. Machine learning has proved particularly useful to perform this task. Fully automatized methods (e.g. deep neural networks) have recently gathered great popularity, even though those methods often lack physical interpretability. In contrast, feature based approaches can provide both well-performing models and understandable causalities with respect to the correlations found between features and physical processes. Efficient feature selection is an essential tool to boost the performance of machine learning models. In this work, we propose a forward selection method in order to compute, evaluate, and characterize better performing features for regression and classification problems. Given the importance of photometric redshift estimation, we adopt it as our case study. We synthetically created 4520 features by combining magnitudes, errors, radii, and ellipticities of quasars, taken from the Sloan Digital Sky Survey (SDSS). We apply a forward selection process, a recursive method in which a huge number of feature sets is tested through a k-Nearest-Neighbours algorithm, leading to a tree of feature sets. The branches of the feature tree are then used to perform experiments with the random forest, in order to validate the best set with an alternative model. We demonstrate that the sets of features determined with our approach improve the performances of the regression models significantly when compared to the performance of the classic features from the literature. The found features are unexpected and surprising, being very different from the classic features. Therefore, a method to interpret some of the found features in a physical context is presented. The feature selection methodology described here is very general and can be used to improve the performance of machine learning models for any regression or classification task.
819. SDSS QSO DR14 spectral properties
ID:
ivo://CDS.VizieR/J/ApJS/249/17
Title:
SDSS QSO DR14 spectral properties
Short Name:
J/ApJS/249/17
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present measurements of the spectral properties for a total of 526,265 quasars, out of which 63% have a continuum signal-to-noise ratio >3pixel^-1^, selected from the fourteenth data release of the Sloan Digital Sky Survey (SDSS-DR14) quasar catalog. We performed a careful and homogeneous analysis of the SDSS spectra of these sources to estimate the continuum and line properties of several emission lines such as H{alpha}, H{beta}, H{gamma}, MgII, CIII], CIV, and Ly{alpha}. From the derived emission line parameters, we estimated single-epoch virial black hole masses (M_BH_) for the sample using H{beta}, MgII, and CIV emission lines. The sample covers a wide range in bolometric luminosity (logLbol; erg/s) between 44.4 and 47.3 and logM_BH_ between 7.1 and 9.9M_{sin}_. Using the ratio of Lbol to the Eddington luminosity as a measure of the accretion rate, the logarithm of the accretion rate is found to be in the range between -2.06 and 0.43. We performed several correlation analyses between different emission line parameters and found them to match the correlation known earlier using smaller samples. We note that strong FeII sources with a large Balmer line width and highly accreting sources with large M BH are rare in our sample. We make an extended and complete catalog available online that contains various spectral properties of 526,265 quasars derived in this work along with other properties culled from the SDSS-DR14 quasar catalog.
820. SDSS QSOs at z<0.8. II. New spectroscopic obs.
ID:
ivo://CDS.VizieR/J/ApJS/221/7
Title:
SDSS QSOs at z<0.8. II. New spectroscopic obs.
Short Name:
J/ApJS/221/7
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present new spectroscopic observations that are part of our continuing monitoring campaign of 88 quasars at z<0.7 whose broad H{beta} lines are offset from their systemic redshifts by a few thousand km/s. These quasars have been considered as candidates for hosting supermassive black hole binaries (SBHBs) by analogy with single-lined spectroscopic binary stars. We present the data and describe our improved analysis techniques, which include an extensive evaluation of uncertainties. We also present a variety of measurements from the spectra that are of general interest and will be useful in later stages of our analysis. Additionally, we take this opportunity to study the variability of the optical continuum and integrated flux of the broad H{beta} line. We compare the variability properties of the SBHB candidates to those of a sample of typical quasars with similar redshifts and luminosities observed multiple times during the Sloan Digital Sky Survey. We find that the variability properties of the two samples are similar (variability amplitudes of 10%-30% on timescales of approximately 1-7 years) and that their structure functions can be described by a common model with parameters characteristic of typical quasars. These results suggest that the broad-line regions of SBHB candidates have a similar extent as those of typical quasars. We discuss the implications of this result for the SBHB scenario and the ensuing constraints on the orbital parameters.