The SDSS-IV extended Baryon Oscillation Spectroscopic Survey: Quasar Target Selection
Adam D. Myers, Nathalie Palanque-Delabrouille, Abhishek Prakash, Isabelle Pâris, Christophe Yeche, Kyle S. Dawson, Jo Bovy, Dustin Lang, David J. Schlegel, Jeff… 展开作者
Adam D. Myers, Nathalie Palanque-Delabrouille, Abhishek Prakash, Isabelle Pâris, Christophe Yeche, Kyle S. Dawson, Jo Bovy, Dustin Lang, David J. Schlegel, Jeffrey A. Newman, Patrick Petitjean, Jean Paul Kneib, Pierre Laurent, Will J. Percival, Ashley J. Ross, Hee-Jong Seo, Jeremy L. Tinker, Eric Armengaud, Joel Brownstein, Etienne Burtin, Zheng Cai, Johan Comparat, Mansi Kasliwal, Shrinivas R. Kulkarni, Russ Laher, David Levitan, Cameron K. McBride, Ian D. McGreer, Adam A. Miller, Peter Nugent, Eran Ofek, Graziano Rossi, John Ruan, Donald P. Schneider, Branimir Sesar, Alina Streblyanska, Jason Surace
备注：
25 pages, 21 figures, 6 tables, Accepted to ApJS after minor revisions and replaced with accepted version. Results unchanged
As part of the Sloan Digital Sky Survey IV the extended Baryon Oscillation Spectroscopic Survey (eBOSS) will improve measurements of the cosmological distance scale by applying the Baryon Acoustic Oscillation (BAO) method to quasar samples. eBOSS will adopt two approaches to target quasars over 7500 sq. deg. First, a "CORE" quasar sample will combine optical selection in ugriz using a likelihood-based routine called XDQSOz, with a mid-IR-optical color-cut. eBOSS CORE selection (to g < 22 OR r < 22) should return ~ 70 quasars per sq. deg. at redshifts 0.9 < z < 2.2 and ~7 z > 2.1 quasars per sq. deg. Second, a selection based on variability in multi-epoch imaging from the Palomar Transient Factory should recover an additional ~3-4 z > 2.1 quasars per sq. deg. to g < 22.5. A linear model of how imaging systematics affect target density recovers the angular distribution of eBOSS CORE quasars over 96.7% (76.7%) of the SDSS North (South) Galactic Cap area. The eBOSS CORE quasar sample should thus be sufficiently dense and homogeneous over 0.9 < z < 2.2 to yield the first few-percent-level BAO constraint near z~1.5. eBOSS quasars at z > 2.1 will be used to improve BAO measurements in the Lyman-alpha Forest. Beyond its key cosmological goals, eBOSS should be the next-generation quasar survey, comprising > 500,000 new quasars and > 500,000 uniformly selected spectroscopically confirmed 0.9 < z < 2.2 quasars. At the conclusion of eBOSS, the SDSS will have provided unique spectra of over 800,000 quasars.
We report the discovery of 13 confirmed two-image quasar lenses from a systematic search for gravitationally lensed quasars in the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS). We adopted a methodology similar to that used in the SDSS Quasar Lens Search (SQLS). In addition to the confirmed lenses, we report 11 quasar pairs with small angular separations ($\lesssim$2") confirmed from our spectroscopy, which are either projected pairs, physical binaries, or possibly quasar lens systems whose lens galaxies have not yet been detected. The newly discovered quasar lens system, SDSS J1452+…
We present the discovery of nine quasars at $z\sim6$ identified in the Sloan Digital Sky Survey (SDSS) imaging data. This completes our survey of $z\sim6$ quasars in the SDSS footprint. Our final sample consists of 52 quasars at $5.7<z\le6.4$, including 29 quasars with $z_{\rm AB}\le20$ mag selected from 11,240 deg$^2$ of the SDSS single-epoch imaging survey (the main survey), 10 quasars with $20\le z_{\rm AB}\le20.5$ selected from 4223 deg$^2$ of the SDSS overlap regions (regions with two or more imaging scans), and 13 quasars down to $z_{\rm AB}\approx22$ mag from the 277 deg$^2$ in Stripe 8…
We here report an identification of SDSS J090152.04+624342.6 as a new "overlapping-trough" iron low-ionization broad absorption line quasar at redshift of $z\sim2.1$. No strong variation of the broad absorption lines can be revealed through the two spectra taken by the Sloan Digital Sky Survey with a time interval of $\sim6$yr. Further optical and infrared spectroscopic study on this object is suggested.
We report the discovery of the quadruply lensed quasar J1433+6007, mined in the SDSS DR12 photometric catalogues using a novel outlier-selection technique, without prior spectroscopic or UV excess information. Discovery data obtained at the Nordic Optical telescope (NOT, La Palma) show nearly identical quasar spectra at $z_s=2.74$ and four quasar images in a fold configuration, one of which sits on a blue arc. The deflector redshift is $z_{l}=0.407,$ from Keck-ESI spectra. We describe the selection procedure, discovery and follow-up, image positions and $BVRi$ magnitudes, and first results and…
Given their extremely large distances and small apparent sizes, quasars are generally considered as objects with near-zero parallax and proper motion. However, some special quasars may have abnormal astrometric characteristics, such as quasar pairs, lensed quasars, AGNs with bright parsec-scale optical jets, which are scientifically interesting objects, such as binary black holes. These quasars may come with astrometric jitter detectable with Gaia data, or significant changes in the position at different wavelengths. In this work, we aim to find these quasar candidates from Gaia EDR3 astrometr…
We present CO(1--0) observations of the high-redshift quasar SDSS J160705+533558 ($z=3.653$) using the Karl G. Jansky Very Large Array (VLA). We detect CO emission associated with the quasar and at $\sim16.8\,\rm kpc$ projected distance from it, separated by $\sim800\,\rm km\,s^{-1}$ in velocity. The total molecular gas mass of this system is $\sim5\times10^{10}\,\rm M_{\odot}$. By comparing our CO detections with previous submillimetre (submm) observations of the source, an offset between the different emission components is revealed: the peak of the submm emission is offset from the quasar a…
We present the result of Subaru Telescope multi-band adaptive optics observations of the complex gravitationally lensed quasar SDSS J1405+0959, which is produced by two lensing galaxies. These observations reveal dramatically enhanced morphological detail, leading to the discovery of an additional object 0. 26'' from the secondary lensing galaxy, as well as three collinear clumps located in between the two lensing galaxies. The new object is likely to be the third quasar image, although the possibility that it is a galaxy cannot be entirely excluded. If confirmed via future observations, it wo…
We report the discovery and confirmation of eight new two-image lensed quasars by the Sloan Digital Sky Survey (SDSS) Quasar Lens Search. The lenses are SDSSJ0904+1512 (image separation θ=1"13, source redshift z_s=1.826), SDSSJ1054+2733 (θ=1"27, z_s=1.452), SDSSJ1055+4628 (θ=1"15, z_s=1.249), SDSSJ1131+1915 (θ=1"46, z_s=2.915), SDSSJ1304+2001 (θ=1"87, z_s=2.175), SDSSJ1349+1227 (θ=3"00, z_s=1.722), SDSSJ1455+1447 (θ=1"73, z_s=1.424), and SDSSJ1620+1203 (θ=2"77, z_s=1.158). Three of them, SDSSJ1055+4628, SDSSJ1455+1447, and SDSSJ1620+1203, satisfy the criteria for constructing our statistical s…
Weak emission line quasars are a rare and puzzling group of objects. In this paper we present one more object of this class found in the Sloan Digital Sky Survey (SDSS). The quasar SDSS J094533.99+100950.1, lying at z = 1.66, has practically no C IV emission line, a red continuum very similar to the second steepest of the quasar composite spectra of Richards et al., is not strongly affected by absorption and the Mg II line, although relatively weak, is strong enough to measure the black hole mass. The Eddington ratio in this object is about 0.45, and the line properties are not consistent with…
We present the discovery of eight quasars at z~6 identified in the Sloan Digital Sky Survey (SDSS) overlap regions. Individual SDSS imaging runs have some overlap with each other, leading to repeat observations over an area spanning >4000 deg^2 (more than 1/4 of the total footprint). These overlap regions provide a unique dataset that allows us to select high-redshift quasars more than 0.5 mag fainter in the z band than those found with the SDSS single-epoch data. Our quasar candidates were first selected as i-band dropout objects in the SDSS imaging database. We then carried out a series of f…
We use a volume-limited sample of quasars in the Sloan Digital Sky Survey (SDSS) DR7 quasar catalog to identify quasar groups and address their statistical significance. This quasar sample has a uniform selection function on the sky and nearly a maximum possible contiguous volume that can be drawn from the DR7 catalog. Quasar groups are identified by using the Friend-of-Friend algorithm with a set of fixed comoving linking lengths. We find that the richness distribution of the richest 100 quasar groups or the size distribution of the largest 100 groups are statistically equivalent with those o…
We present a sample of 8498 quasars with both SDSS $ugriz$ optical and UKIDSS $YJHK$ near-IR photometric data. With this sample, we obtain the median colour-z relations based on 7400 quasars with magnitude uncertainties less than 0.1mag in all bands. By analyzing the quasar colours, we propose an empirical criterion in the $Y-K$ vs. $g-z$ colour-colour diagram to separate stars and quasars with redshift $z<4$, and two other criteria for selecting high-z quasars. Using the SDSS-UKIDSS colour-z relations, we estimate the photometric redshifts of 8498 SDSS-UKIDSS quasars, and find that 85.0% of t…
We here report an identification of SDSSJ141324+530527.0 (SBS1411+533) at $z=0.456344$ as a new "changing-look" quasar with a "turn-on" spectral type transition from Type-1.9/2 to Type-1 within a rest frame time scale of 1-10 yr by a comparison of our new spectroscopic observation and the Sloan Digital Sky Survey (SDSS) archive data base. The SDSS DR7 spectrum taken in 2003 is dominated by a starlight emission from host galaxies redward of the Balmer limit, and has non-detectable broad H$β$ line. The new spectrum taken by us on June 1st, 2017 and SDSS DR14 spectrum taken on May 29, 2017 indica…
We report the discovery of a quasar close to SDSS J0927+2943 (z = 0.713), which is a massive binary / recoiling black hole candidate. The companion quasar is at a projected distance of 125 h_70^{-1} kpc and exhibits a radial velocity difference of ~1400 km/s with respect to the known quasar. We discuss the nature of this peculiar quasar pair and the properties of its environment. We propose that the overall system is caught in the process of ongoing structure formation.
Using high resolution VLT spectra, we study the multi-component outflow systems of two quasars exhibiting intrinsic Fe II absorption (QSO 2359-1241 and SDSS J0318-0600). From the extracted ionic column densities and using photoionization modeling we determine the gas density, total column density, and ionization parameter for several of the components. For each object the largest column density component is also the densest, and all other components have densities of roughly 1/4 of that of the main component. We demonstrate that all the absorbers lie roughly at the same distance from the sourc…
We present a catalog of 37,842 quasars in the SDSS Data Release 7, which have counterparts within 6" in the 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 per…
We present a compilation of HST images of 58 luminous SDSS type 2 AGNs at 0.3<z<0.4. 42 of them are type 2 quasars, which are a good representation of all optically selected SDSS type 2 quasars in this range. We find that the majority of the host galaxies are ellipticals (30/42 or 71%). This is consistent with studies of radio loud and radio quiet type 1 quasars which show that their host galaxies are in general ellipticals. A significant fraction of type 2 quasars (>25/42 or >59%) show clear signatures of morphological disturbance which are in most cases identified with merger/interaction pro…
We discuss whether modern machine learning methods can be used to characterize the physical nature of the large number of objects sampled by the modern multi-band digital surveys. In particular, we applied the MLPQNA (Multi Layer Perceptron with Quasi Newton Algorithm) method to the optical data of the Sloan Digital Sky Survey - Data Release 10, investigating whether photometric data alone suffice to disentangle different classes of objects as they are defined in the SDSS spectroscopic classification. We discuss three groups of classification problems: (i) the simultaneous classification of ga…
Quasars that exhibit blue-shifted, broad absorption lines (BAL QSOs) are an important probe of black hole feedback on galaxy evolution. Yet the presence of BALs is also a complication for large, spectroscopic surveys that use quasars as cosmological probes because the BAL features can affect redshift measurements and contaminate information about the matter distribution in the Lyman-$α$ forest. We present a new BAL QSO catalog for quasars in the Sloan Digital Sky Survey (SDSS) Data Release 14 (DR14). As the SDSS DR14 quasar catalog has over 500,000 quasars, we have developed an automated BAL c…
SDSS J2222+2745 is a galaxy cluster at z=0.49, strongly lensing a quasar at z=2.805 into six widely separated images. In recent HST imaging of the field, we identify additional multiply lensed galaxies, and confirm the sixth quasar image that was identified by Dahle et al. (2013). We used the Gemini North telescope to measure a spectroscopic redshift of z=4.56 of one of the secondary lensed galaxies. These data are used to refine the lens model of SDSS J2222+2745, compute the time delay and magnifications of the lensed quasar images, and reconstruct the source image of the quasar host and a se…
The distribution of SDSS quasars is described. The dependence of observational number of quasars within distances to an observer less than r on distance r is found to be the power law with correlation dimension value equal 2,71 in redshift range 0,35 < z < 2,30 for the flat Universe filled with cold dust. The quasar distribution on the celestial sphere is characterized by power laws as well with correlation dimension value equal from 1,49 to 1,58 for different redshift layers in the same range. These properties are evidences of fractality.
(Abridged for arXiv) We report the discovery of an unusual, extremely dust-rich and metal-strong damped \lya absorption system (DLA) at a redshift $z_{a}=2.4596$ toward the quasar SDSS J115705.52+615521.7 (hereafter J1157+6155) with an emission-line redshift $z_{e}=2.5125$. Its neutral hydrogen column density $N_{\hi} = 10^{21.8\pm0.2}$ cm$^{-2}$ is among the highest values measured in quasar DLAs. The measured metal column density is $N_{ZnII}\approx 10^{13.8}$ cm$^{-2}$, which is about 1.5 times larger than the largest value in any previously observed quasar DLAs. The best-fit curve is a MW-…
Starting from the quasar sample of the Sloan Digital Sky Survey (SDSS) for which the CIV line is observed, we use an analysis scheme to derive the z-dependence of the maximum mass of active black holes, which overcomes the problems related to the Malmquist bias. The same procedure is applied to the low redshift sample of SDSS quasars for which Hbeta measurements are available. Combining with the results from the previously studied MgII sample, we find that the maximum mass of the quasar population increases as (1+z)^(1.64+/-0.04) in the redshift range 0.1<z<4, which includes the epoch of maxim…
We have collected near-infrared to X-ray data of 20 multi-epoch heavily reddened SDSS quasars to investigate the physical mechanism of reddening. Of these, J2317+0005 is found to be a UV cutoff quasar. Its continuum, which usually appears normal, decreases by a factor 3.5 at 3000Å, compared to its more typical bright state during an interval of 23 days. During this sudden continuum cut-off, the broad emission line fluxes do not change, perhaps due to the large size of the Broad Line Region (BLR), r > 23 / (1+z) days. The UV continuum may have suffered a dramatic drop out. However, there are so…
We report the discovery of a gravitationally lensed quasar identified serendipitously in the Sloan Digital Sky Survey (SDSS). The object, SDSS J094604.90+183541.8, was initially targeted for spectroscopy as a luminous red galaxy, but the SDSS spectrum has the features of both a z=0.388 galaxy and a z=4.8 quasar. We have obtained additional imaging that resolves the system into two quasar images separated by 3.06 arcsec and a bright galaxy that is strongly blended with one of the quasar images. We confirm spectroscopically that the two quasar images represent a single lensed source at z=4.8 wit…
A systematic investigation of the relationship between different redshift estimation schemes for more than 91000 quasars in the Sloan Digital Sky Survey (SDSS) Data Release 6 (DR6) is presented. The publicly available SDSS quasar redshifts are shown to possess systematic biases of Dz/(1+z)>=0.002 (600km/s) over both small (dz~0.1) and large (dz~1) redshift intervals. Empirical relationships between redshifts based on i) CaII H & K host galaxy absorption, ii) quasar [OII] 3728, iii) [OIII] 4960,5008 emission, and iv) cross-correlation (with a master quasar template) that includes, at increasing…
We present the first luminous, spatially resolved binary quasar that clearly inhabits an ongoing galaxy merger. SDSS J125455.09+084653.9 and SDSS J125454.87+084652.1 (SDSS J1254+0846 hereafter) are two luminous z=0.44 radio quiet quasars, with a radial velocity difference of just 215 km/s, separated on the sky by 21 kpc in a disturbed host galaxy merger showing obvious tidal tails. The pair was targeted as part of a complete sample of binary quasar candidates with small transverse separations drawn from SDSS DR6 photometry. We present follow-up optical imaging which shows broad, symmetrical ti…
We present the discovery of six new quasars at z~6 selected from the Sloan Digital Sky Survey (SDSS) southern survey, a deep imaging survey obtained by repeatedly scanning a stripe along the celestial equator. The six quasars are about two magnitudes fainter than the luminous z~6 quasars found in the SDSS main survey and one magnitude fainter than the quasars reported in Paper I (Jiang et al. 2008). Four of them comprise a complete flux-limited sample at 21<z_AB<21.8 over an effective area of 195 deg^2. The other two quasars are fainter than z_AB=22 and are not part of the complete sample. The…
We present mass functions of distant actively accreting supermassive black holes residing in luminous quasars discovered in the Large Bright Quasar Survey, the Bright Quasar Survey, and the Fall Equatorial Stripe of the Sloan Digital Sky Survey (SDSS). The quasars cover a wide range of redshifts (0 <~ z <= 5) and were subject to different selection criteria and flux density limits. These samples are thus complementary and can help us gain additional insight on the true underlying black hole mass distribution, free from selection effects and mass estimation errors through future studies. We see…
We study the small population of z>2.7 quasars detected by GALEX, whose far-UV emission is not extinguished by intervening HI Lyman limit systems. These quasars are of particular importance to detect intergalactic HeII absorption along their sightlines. We correlate verified z>2.7 quasars to the GALEX GR4 source catalog, yielding 304 S/N>3 sources. However, ~50% of these are only detected in the GALEX NUV band, signaling the truncation of the FUV flux by low-redshift Lyman limit systems. We exploit the GALEX UV color to cull the most promising targets for follow-up studies, with blue (red) GAL…
We present the SDSS-XDQSO quasar targeting catalog for efficient flux-based quasar target selection down to the faint limit of the Sloan Digital Sky Survey (SDSS) catalog, even at medium redshifts (2.5 <~ z <~ 3) where the stellar contamination is significant. We build models of the distributions of stars and quasars in flux space down to the flux limit by applying the extreme-deconvolution method to estimate the underlying density. We convolve this density with the flux uncertainties when evaluating the probability that an object is a quasar. This approach results in a targeting algorithm tha…
In a sample of 60 quasars selected from Sloan Digital Sky Survey (SDSS) with at least six-epoch spectroscopy, we investigate the variability of emission lines and continuum luminosity at various aspects. A strong anti-correlation between the variability and continuum luminosity at 2500 Å is found for the sample, which is consistent with previous works. In individual sources, we find that half of the sample objects have a trend of being bluer-when-brighter trend (BWB), while the remaining half exhibit redder-when-brighter trend (RWB). Although the mechanism for RWB is unclear, the effects of ho…
We present optical spectroscopy of the nearest quasar pair listed in the 13th edition of the Veron-Cetty & Veron catalogue, i.e. the two quasars SDSS J15244+3032 and RXS J15244+3032 (redshift z~0.27, angular separation ~7 arcsec, and line-of-sight velocity difference ~1900 km/s). This system would be an optimal candidate to investigate the mutual interaction of the host galaxies with ground based optical imaging and spectroscopy. However, new optical data demonstrate that RXS J15244+3032 is indeed a star of spectral type G. This paper includes data gathered with the Asiago 1.82m telescope (Cim…
We compiled a sample of 60 quasars with spectroscopy on at least six epochs from the Sloan Digital Sky Survey (SDSS) to study the variabilities of the spectral shape, the continuum and the emission lines luminosity. In this paper, we present the results of SDSS J030639.57+000343.1. We found a strong anti-correlation between the continuum luminosity at $5100 Å$ and the spectral index, implying a bluer-when-brighter trend. The luminosity of the broad $\rm H_α$ line is proportion to the continuum luminosity at $5100 Å$. Correspondingly, we did not find strong correlation between the equivalent wi…
In this paper, we report on two C IV narrow absorption systems emerging from the spectrum of the quasar SDSS J095254.10 +021932.8, which are located at $z_{\rm abs}=2.0053$ and $z_{\rm abs}=1.8011$, respectively. These features have velocity offsets of $\rm \sim 13,800$ and $\rm \sim 34,700~km~s^{-1}$ with respect to the quasar, and show obviously partial coverage to the background emission sources. The two C IV absorption systems are imprinted on the spectrum obtained by the Sloan Digital Sky Survey (SDSS) III on 2011 March 25, which cannot be observed from the spectrum obtained by SDSS-I/II …
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, …
We present first results from our study of the properties of ~400 low redshift (z < 0.5) quasars, based on a large homogeneous dataset derived from the Stripe 82 area of the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7). For this sky region, deep (r~22.4) u,g,r,i,z images are available, up to ~2 mag deeper than standard SDSS images, allowing us to study both the host galaxies and the Mpc-scale environments of the quasars. This sample greatly outnumbers previous studies of low redshift quasar hosts, from the ground or from space. Here we report the preliminary results for the quasar host…
We present spectroscopic analysis of the broad absorption line outflow in quasar SDSS J1512+1119. In particular, we focus our attention on a kinematic component in which we identify PV and SIV/SIV* absorption troughs. The shape of the unblended phosphorus doublet troughs and the three SIV/SIV* troughs allow us to obtain reliable column density measurements for these two ions. Photoionization modelling using these column densities and those of HeI* constrain the abundance of phosphorus to the range of 0.5-4 times the solar value. The total column density, ionization parameter and metalicity inf…
We report the discovery of four doubly imaged quasar lenses. All the four systems are selected as lensed quasar candidates from the Sloan Digital Sky Survey data. We confirm their lensing hypothesis with additional imaging and spectroscopic follow-up observations. The discovered lenses are SDSS J0743+2457 with the source redshift z_s=2.165, the lens redshift z_l=0.381, and the image separation theta=1.034", SDSS J1128+2402 with z_s=1.608 and theta=0.844", SDSS J1405+0959 with z_s=1.810, z_l~0.66, and theta=1.978", and SDSS J1515+1511 with z_s=2.054, z_l=0.742, and theta=1.989". It is difficult…
Absorption along quasar sightlines remains among the most sensitive direct measures of HeII reionization in much of the intergalactic medium (IGM). Until recently, fewer than a half-dozen unobscured quasar sightlines suitable for the HeII Gunn-Peterson test were known; although these handful demonstrated great promise, the small sample size limited confidence in cosmological inferences. We have recently added nine more such clean HeII quasars, exploiting SDSS quasar samples, broadband UV imaging from GALEX, and high-yield UV spectroscopic confirmations from HST. Here we markedly expand this ap…
We cross-correlate the SDSS DR3 quasar sample with FIRST and the Vestergaard et al. black hole (BH) mass sample to compare the mean accretion histories of optical and radio quasars. We find significant statistical evidence that radio quasars have a higher mean Eddington ratio Lambda at z > 2 with respect to optical quasars, while the situation is clearly reverse at z < 1. At z > 2 radio quasars happen to be less massive than optical quasars; however, as redshift decreases radio quasars appear in increasingly more massive BHs with respect to optical quasars. These two trends imply that radio so…
Identifications of quasars at intermediate redshifts (2.2<z<3.5) are inefficient in most previous quasar surveys as their optical colors are similar to those of stars. The near-IR K-band excess technique has been suggested to overcome this difficulty. Our study also proposed to use optical/near-IR colors for selecting z<4 quasars. To this method, we selected 105 unidentified bright targets with i<18.5 from the quasar candidates of SDSS DR6 with both SDSS ugriz optical and UKIDSS YJHK near-IR photometric data, which satisfy our proposed Y-K/g-z criterion and have photometric redshifts between 2…
In the Sloan Digital Sky Survey (SDSS) quasars are targeted using colors and anything that can cause the identifying characteristics of the colors to disappear can create problems in the source selection process. Quasar spectra contain strong emission lines that can seriously affect the colors in photometric systems in which the transmission characteristics vary abruptly and significantly with redshift. When a strong line crosses a gap between two filter passbands the color effects induced by the line change abruptly, and there is also a dimming in apparent brightness compared to those redshif…
We present long-slit spectroscopy, continuum and [OIII]5007 imaging data obtained with the Very Large Telescope and the Gran Telescopio Canarias of the type 2 quasar SDSS J0123+00 at z=0.399. The quasar lies in a complex, gas-rich environment. It appears to be physically connected by a tidal bridge to another galaxy at a projected distance of ~100 kpc, which suggests this is an interacting system. Ionized gas is detected to a distance of at least ~133 kpc from the nucleus. The nebula has a total extension of ~180 kpc. This is one of the largest ionized nebulae ever detected associated with an …
We present a model for spectrophotometric calibration errors in observations of quasars from the third generation of the Sloan Digital Sky Survey (SDSS-III) Baryon Oscillation Spectroscopic Survey (BOSS) and describe the correction procedure we have developed and applied to this sample. Calibration errors are primarily due to atmospheric differential refraction and guiding offsets during each exposure. The corrections potentially reduce the systematics for any studies of BOSS quasars, including the measurement of baryon acoustic oscillations using the Lyman-$α$ forest. Our model suggests that,…
We present a catalog of over 130,000 quasars candidates with NIR photometric properties, with an areal coverage of approximately 1,200 deg^2. This is achieved by matching the Sloan Digital Sky Survey (SDSS) in the optical ugriz bands, to the UKIRT Infrared Digital Sky Survey (UKIDSS) Large Area Survey (LAS) in the near-infrared YJHK bands. We match the ~1 million SDSS DR6 Photometric Quasar catalog to Data Release 3 of the UKIDSS LAS (ULAS), and produce a catalog with 130,827 objects with detections in one or more NIR bands, of which 74,351 objects have optical and K-band detections and 42,133…
We report on a dusty Mg~II absorber associated with the quasar SDSSJ003545.13+011441.2 (hereafter J0035+0114) at $z$=1.5501, which is the strongest one among the three Mg~II absorbers along the sight line of quasar. The two low redshift intervening absorbers are at $z$=0.7436, 0.5436, respectively. Based on the photometric and spectroscopic data of Sloan Digital Sky Survey (hereafter SDSS), we infer the rest frame color excess E(\bv) due to the associated dust is more than 0.07 by assuming a Small Magellanic Cloud (hereafter SMC) type extinction curve. Our follow-up moderate resolution spectro…
We present a measurement of the Type I quasar luminosity function at z=5 using a large sample of spectroscopically confirmed quasars selected from optical imaging data. We measure the bright end (M_1450<-26) with Sloan Digital Sky Survey (SDSS) data covering ~6000 deg^2, then extend to lower luminosities (M_1450<-24) with newly discovered, faint z~5 quasars selected from 235 deg^2 of deep, coadded imaging in the SDSS Stripe 82 region (the celestial equator in the Southern Galactic Cap). The faint sample includes 14 quasars with spectra obtained as ancillary science targets in the SDSS-III Bary…
We present an estimate of the projected two-point correlation function (2PCF) of quasars in the Sloan Digital Sky Survey (SDSS) over the full range of one- and two-halo scales, 0.02-120 Mpc/h. This was achieved by combining data from SDSS DR7 on large scales and Hennawi et al. (2006; with appropriate statistical corrections) on small scales. Our combined clustering sample is the largest spectroscopic quasar clustering sample to date, containing ~48,000 quasars in the redshift range 0.4<z<2.5 with median redshift 1.4. We interpret these precise 2PCF measurements within the halo occupation distr…
The results of a large area, ~600 deg^2, K-band flux-limited spectroscopic survey for luminous quasars are presented. The survey utilises the UKIRT Infrared Deep Sky Survey (UKIDSS) Large Area Survey (LAS) in regions of sky within the Sloan Digital Sky Survey (SDSS) footprint. The K-band excess (KX) of all quasars with respect to Galactic stars is exploited in combination with a photometric redshift/classification scheme to identify quasar candidates for spectroscopic follow-up observations. The data contained within this investigation will be able to provide new constraints on the fraction of…
In this letter, we present for the first time, the discovery of the disappearance of a narrow Mg II $λ\lambda2796,2803$ absorption system from the spectra of quasar SDSS J165501.31+260517.4 ($z_{\rm e}=1.8671$). This absorber is located at $z_{\rm abs} =1.7877$, and has a velocity offset of $8,423\rm ~km~s^{-1}$ with respect to the quasar. According to the velocity offset and the line variability, this narrow Mg II $λ\lambda2796,2803$ absorption system is likely intrinsic to the quasar. Since the corresponding UV continuum emission and the absorption lines of another narrow Mg II $λ\lambda2796…
We report measurements of the scale of cosmic homogeneity ($r_{h}$) using the recently released quasar sample of the sixteenth data release of the Sloan Digital Sky Survey (SDSS-IV DR16). We perform our analysis in 2 redshift bins lying in the redshift interval $2.2 < z < 3.2$ by means of the fractal dimension $D_2$. By adopting the usual assumption that $r_{h}$ is obtained when $D_2 \sim 2.97$, that is, within 1% of $D_2=3$, we find the cosmic homogeneity scale with a decreasing trend with redshift, and in good agreement with the $Λ$CDM prediction. Our results confirm the presence of a homoge…
We study the origin of absorption features on the blue side of the C IV broad emission line of the large-separation lensed quasar SDSS J1029+2623 at z_em ~ 2.197. The quasar images, produced by a foreground cluster of galaxies, have a maximum separation angle of ~ 22".5. The large angular separation suggests that the sight-lines to the quasar central source can go through different regions of outflowing winds from the accretion disk of the quasar, providing a unique opportunity to study the structure of outflows from the accretion disk, a key ingredient for the evolution of quasars as well as …
The quasar SDSS J133401.39+331534.3 at z = 2.426 is found to be a two-image gravitationally lensed quasar with the image separation of 0.833. The object is first identified as a lensed quasar candidate in the Sloan Digital Sky Survey Quasar Lens Search, and then confirmed as a lensed system from follow-up observations at the Subaru and University of Hawaii 2.2-meter telescopes. We estimate the redshift of the lensing galaxy to be 0.557 based on absorption lines in the quasar spectra as well as the color of the galaxy. In particular, we observe the system with the Subaru Telescope AO188 adaptiv…
We report on the discovery of a Type 1 quasar, SDSS 0956+5128, with a surprising combination of extreme velocity offsets. SDSS 0956+5128 is a broad-lined quasar exhibiting emission lines at three substantially different redshifts: a systemic redshift of z ~ 0.714 based on narrow emission lines, a broad MgII emission line centered 1200 km/s bluer than the systemic velocity, at z ~ 0.707, and broad Hαand Hβemission lines centered at z ~ 0.690. The Balmer line peaks are 4100 km/s bluer than the systemic redshift. There are no previously known objects with such an extreme difference between broad …
We present a compilation of properties of the 105,783 quasars in the SDSS Data Release 7 (DR7) quasar catalog. In this value-added product, we compile continuum and emission line measurements around the Halpha, Hbeta, MgII and CIV regions, as well as other quantities such as radio properties, broad absorption line quasar (BALQSO) flags, and disk emitters. We also compile virial black hole mass estimates based on various calibrations. For the fiducial virial mass estimates we use the Vestergaard & Peterson (VP06) calibrations for Hbeta and CIV, and our own calibration for MgII which matches the…
The SDSS-III BOSS Quasar survey will attempt to observe z>2.15 quasars at a density of at least 15 per square degree to yield the first measurement of the Baryon Acoustic Oscillations in the Ly-alpha forest. To help reaching this goal, we have developed a method to identify quasars based on their variability in the u g r i z optical bands. The method has been applied to the selection of quasar targets in the SDSS region known as Stripe 82 (the Southern equatorial stripe), where numerous photometric observations are available over a 10-year baseline. This area was observed by BOSS during Septem…
The quasar sample of the fourteenth data release of the Sloan Digital Sky Survey (SDSS-IV DR14) is used to determine the cosmic homogeneity scale in the redshift range $0.80<z<2.24$. We divide the sample into 4 redshift bins, each one with $N_{\rm q} \geq 19,000$ quasars, spanning the whole redshift coverage of the survey and use two correlation function estimators to measure the scaled counts-in-spheres and its logarithmic derivative, i.e., the fractal correlation dimension, $D_2$. Using the $Λ$CDM cosmology as the fiducial model, we first estimate the redshift evolution of quasar bias and th…
We investigate the range of covering factors (determined from the ratio of IR to UV/optical luminosity) seen in luminous type 1 quasars using a combination of data from the WISE, UKIDSS and SDSS surveys. Accretion disk (UV/optical) and obscuring dust (IR) luminosities are measured via the use of a simple three component SED model. We use these estimates to investigate the distribution of covering factors and its relationship to both accretion luminosity and IR SED shape. The distribution of covering factors (f_C) is observed to be log-normal, with a bias-corrected mean of <log10 f_C>=-0.41 and…
Context. Although a bluer-when-brighter trend is commonly observed in blazars, the opposite trend of redder-when-brighter has also been found in some blazars. Aims. We investigate the frequency of the redder-when-brighter trend in flat-spectrum radio quasars (FSRQs). Methods. We investigate the optical variability of 29 FSRQs in the SDSS Stripe 82 region using SDSS DR7 released multi-epoch data covering about nine years. We determined the spectral index by fitting a powerlaw to SDSS ugriz photometric data, and explored the relationship between the spectral index and source brightness. Results.…
