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Register a new userFive New High-Redshift Quasar Lenses from the Sloan Digital Sky Survey
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We report the discovery of five gravitationally lensed quasars from the Sloan Digital Sky Survey (SDSS). All five systems are selected as two-image lensed quasar candidates from a sample of high-redshift (z>2.2) SDSS quasars. We confirmed their lensing nature with additional imaging and spectroscopic observations. The new systems are SDSS J0819+5356 (source redshift z_s=2.237, lens redshift z_l=0.294, and image separation theta=4.04), SDSS J1254+2235 (z_s=3.626, theta=1.56), SDSS J1258+1657 (z_s=2.702, theta=1.28), SDSS J1339+1310 (z_s=2.243, theta=1.69), and SDSS J1400+3134 (z_s=3.317, theta=1.74). We estimate the lens redshifts of the latter four systems to be z_l=0.2-0.8 from the colors and magnitudes of the lensing galaxies. We find that the image configurations of all systems are well reproduced by standard mass models. Although these lenses will not be included in our statistical sample of z_s<2.2 lenses, they expand the number of lensed quasars which can be used for high-redshift galaxy and quasar studies.
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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 to estimate the lens redshift of SDSS J1128+2402 from the current data. Two of the four systems (SDSS J1405+0959 and SDSS J1515+1511) are included in our final statistical lens sample to derive constraints on dark energy and the evolution of massive galaxies.
We present observations at 250 GHz (1.2 mm), 43 GHz, and 1.4 GHz of a sample of 41 QSOs at z > 3.7 found in the Sloan Digital Sky Survey. We detect 16 sources with a 250 GHz flux density greater than 1.4 mJy. The combination of centimeter and millimeter wavelength observations indicates that the 250 GHz emission is most likely thermal dust emission. Assuming a dust temperature of 50 K, the implied dust masses for the 16 detected sources are in the range 1.5e8 to 5.9e8 Msun, and the dust emitting regions are likely to be larger than 1 kpc in extent. The radio-through-optical spectral energy distributions for these sources are within the broad range defined by lower redshift, lower optical luminosity QSOs. We consider possible dust heating mechanisms, including UV emission from the active nucleus (AGN) and a starburst concurrent with the AGN, with implied star formation rates between 500 and 2000 Msun/year.
We report the discovery of a new two-image gravitationally lensed quasar, SDSS J024634.11-082536.2 (SDSS J0246-0825). This object was selected as a lensed quasar candidate from the Sloan Digital Sky Survey (SDSS) by the same algorithm that was used to discover other SDSS lensed quasars (e.g., SDSS J0924+0219). Multicolor imaging with the Magellan Consortiums Walter Baade 6.5-m telescope and the spectroscopic observations using the W. M. Keck Observatorys Keck II telescope confirm that SDSS J0246-0825 consists of two lensed images ($Delta{theta}=$1farcs04) of a source quasar at z=1.68. Imaging observations with the Keck telescope and the Hubble Space Telescope reveal an extended object between the two quasar components, which is likely to be a lensing galaxy of this system. From the absorption lines in the spectra of quasar components and the apparent magnitude of the galaxy, combined with the expected absolute magnitude from the Faber-Jackson relation, we estimate the redshift of the lensing galaxy to be z=0.724. A highly distorted ring is visible in the Hubble Space Telescope images, which is likely to be the lensed host galaxy of the source quasar. Simple mass modeling predicts the possibility that there is a small (faint) lensing object near the primary lensing galaxy.
(Abridged) We study the two-point correlation function of a uniformly selected sample of 4,426 luminous optical quasars with redshift $2.9 le zle 5.4$ selected over 4041 deg$^2$ from the Fifth Data Release of the Sloan Digital Sky Survey. For a real-space correlation function of the form $xi(r)=(r/r_0)^{-gamma}$, the fitted parameters in comoving coordinates are $r_0 = 15.2 pm 2.7 h^{-1}$ Mpc and $gamma = 2.0 pm 0.3$, over a scale range $4le r_ple 150 h^{-1}$ Mpc. Thus high-redshift quasars are appreciably more strongly clustered than their $z approx 1.5$ counterparts, which have a comoving clustering length $r_0 approx 6.5 h^{-1}$ Mpc. Dividing our sample into two redshift bins: $2.9le zle 3.5$ and $zge 3.5$, and assuming a power-law index $gamma=2.0$, we find a correlation length of $r_0 = 16.9 pm 1.7 h^{-1}$ Mpc for the former, and $r_0 = 24.3 pm 2.4 h^{-1}$ Mpc for the latter. Following Martini & Weinberg, we relate the clustering strength and quasar number density to the quasar lifetimes and duty cycle. Using the Sheth & Tormen halo mass function, the quasar lifetime is estimated to lie in the range $4sim 50$ Myr for quasars with $2.9le zle 3.5$; and $30sim 600$ Myr for quasars with $zge 3.5$. The corresponding duty cycles are $0.004sim 0.05$ for the lower redshift bin and $0.03sim 0.6$ for the higher redshift bin. The minimum mass of halos in which these quasars reside is $2-3times 10^{12} h^{-1}M_odot$ for quasars with $2.9le zle 3.5$ and $4-6times 10^{12} h^{-1}M_odot$ for quasars with $zge 3.5$.
We perform a systematic search for high-redshift ($z >$ 1.5) extreme variability quasars (EVQs) using repeat spectra from the Sixteenth Data Release of Sloan Digital Sky Survey, which provides a baseline spanning up to $sim$18 yrs in the observed frame. We compile a sample of 348 EVQs with a maximum continuum variability at rest frame 1450 Angstrom of more than 100% (i.e., $delta$V $equiv$ (Max$-$Min)/Mean $>$1). The EVQs show a range of emission line variability, including 23 where at least one line in our redshift range disappears below detectability, which can then be seen as analogous to low-redshift changing-look quasars (CLQs). Importantly, spurious CLQs caused by SDSS problematic spectral flux calibration, e.g., fiber drop issue, have been rejected. The similar properties (e.g., continuum/line, difference-composite spectra and Eddington ratio) of normal EVQs and CLQs, implies that they are basically the same physical population with analogous intrinsic variability mechanisms, as a tail of a continuous distribution of normal quasar properties. In addition, we find no reliable evidence ($lesssim$ 1$sigma$) to support that the CLQs are a subset of EVQs with less efficient accretion. Finally, we also confirm the anti-breathing of C IV (i.e., line width increases as luminosity increases) in EVQs, and find that in addition to $sim$ 0.4 dex systematic uncertainty in single-epoch C IV virial black hole mass estimates, an extra scatter of $sim$ 0.3 dex will be introduced by extreme variability.
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