Quasar Systems Research Articles

Two New Gravitationally Lensed Double Quasars from the Sloan Digital Sky Survey

We report the discoveries of the two-image gravitationally lensed quasars, SDSS J0746+4403 and SDSS J1406+6126, selected from the Sloan Digital Sky Survey (SDSS). SDSS J0746+4403, which will be included in our lens sample for statistics and cosmology, has a source redshift of z_s=2.00, an estimated lens redshift of z_l~0.3, and an image separation of 1.08. SDSS J1406+6126 has a source redshift of z_s=2.13, a spectroscopically measured lens redshift of z_l=0.27, and an image separation of 1.98. We find that the two quasar images of SDSS J1406+6126 have different intervening MgII absorption strengths, which are suggestive of large variations of absorbers on kpc scales. The positions and fluxes of both the lensed quasar systems are easily reproduced by simple mass models with reasonable parameter values. These objects bring to 18 the number of lensed quasars that have been discovered from the SDSS data.

ChandraObservations of SDSS J1004+4112: Constraints on the Lensing Cluster and Anomalous X‐Ray Flux Ratios of the Quadruply Imaged Quasar

We present results from Chandra observations of SDSS J1004+4112, a strongly lensed quasar system with a maximum image separation of 15''. All four bright images of the quasar, as well as resolved X-ray emission originating from the lensing cluster, are clearly detected. The emission from the lensing cluster extends out to approximately 15. We measure the bolometric X-ray luminosity and temperature of the lensing cluster to be 4.7 × 1044 ergs s-1 and 6.4 keV, consistent with the luminosity-temperature relation for distant clusters. The mass estimated from the X-ray observation shows excellent agreement with the mass derived from gravitational lensing. The X-ray flux ratios of the quasar images differ markedly from the optical flux ratios, and the combined X-ray spectrum of the images possesses an unusually strong Fe Kα emission line, both of which are indicative of microlensing.

The Evolution of Neutral Gas in the Universe

AbstractWe give references to some of our work on the properties and evolution of the neutral gas component of the Universe (see reference list). The bulk of the observed neutral gas has been detected by identifying intervening damped Lyα (DLA) quasar absorption-line systems with N(H) ≥2 × 1020 atoms cm−2. We also present some initial results from a program to identify DLA absorbers near redshift z = 0.5 using Hubble Space Telescope ACS prism spectra (see Figure 1).

Dissecting the Circumstellar Environment of γ‐Ray Burst Progenitors

We investigate properties of the interstellar medium (ISM) in galaxies hosting long-duration γ-ray bursts (GRBs) from an analysis of atomic species (Mg0, Fe0) and excited fine-structure levels of ions (e.g., Si+). Our analysis is guided primarily by echelle observations of GRB 050730 and GRB 051111. These sight lines exhibit fine-structure transitions of O0, Si+, and Fe+ gas that have not yet been detected in intervening quasar absorption-line systems. Our results indicate that the gas with large Mg I equivalent width (e.g., GRB 051111) must occur at distances 50 pc from GRB afterglows to avoid photoionization. We examine the mechanisms for fine-structure excitation and find that two processes can contribute: (1) indirect UV pumping by the GRB afterglow provided a far-UV intensity in excess of 106 times the Galactic radiation field; and (2) collisional excitation in gas with electron density ne > 104 cm-3. The observed abundances of excited ions are well explained by UV pumping with the gas at r ~ a few hundred pc from the afterglow for GRB 051111 and r < 100 pc for GRB 050730, without invoking extreme gas density and temperature in the ISM. We show that UV pumping alone provides a simple explanation for all reported detections of excited ions in GRB afterglow spectra. The presence of strong fine-structure transitions therefore may offer little constraint for the gas density or temperature. We discuss additional implications of UV pumping including its impact on chemical abundance measurements, new prospects for observing line-strength variability, and future prospects for studying the gas density and temperature. Finally, we list a series of criteria that can distinguish between the mechanisms of UV pumping and collisional excitation.

Near-Infrared Search for CivAbsorption Counterparts along the Lines of Sight to Pair Quasars

We carried out a Subaru and UKIRT near-infrared imaging survey for Hα-emitting galaxies around two pair quasar systems (Q0301-005/Q0302-003 and Q2343+125/Q2344+125) and a triple quasar system (KP 76/KP 77/KP 78). Narrowband near-infrared filters covering the Hα emission expected for galaxies at the confirmed C IV absorption redshift toward the quasar systems were used for this survey. These quasar pairs or triplet are separated at most by 17' (~5 h-1 Mpc in proper distance) from each other on the sky and have common C IV absorption lines at almost identical redshifts at z = 2.24–2.43, which suggests there could be a megaparsec-scale absorbing system such as a cluster, or a group, of galaxies that covers all the lines of sight to the pair/triple quasars. Using narrowband deep images, we detected five candidates for Hα-emitting galaxies around two of the six fields, Q2343+125 and Q2344+125, whose apparent star formation rates are extremely high, 20–466 M⊙ yr-1. However, all or most of them are not likely to be galaxies at the absorption redshift but galaxies at lower redshift, because of their extreme brightness. In the fields of the other quasars, we detected no star-forming galaxies, nor did we find any number excess of galaxy counts around them. These nondetections could be because the luminosities and star formation rates of galaxies are lower than the detection limits of our observations (K' > 21 and SFR < 1.8–240 h-2 M⊙ yr-1). They could be located outside of the observed field around Q0301 and Q0302, since our targeting field covers only 2% of this pair quasar field. But this is not the case for the other pair/triple quasar fields, because we found large field coverage fractions (~33%–75%). Otherwise, most C IV absorption lines could be ascribed not to clusters of galaxies but to isolated star-forming pockets, far from bright galaxies, that could be analogous objects to weak Mg II absorbers.

Size Is Everything: Universal Features of Quasar Microlensing with Extended Sources

We examine the effect that the shape of the source brightness profile has on the magnitude fluctuations of images in quasar lens systems due to microlensing. We do this by convolving a variety of accretion disk models (including Gaussian disks, uniform disks, cones, and a Shakura-Sunyaev thermal model) with two magnification maps in the source plane, one with convergence κ = 0.4 and shear γ = 0.4 (positive parity) and the other with κ = γ = 0.6 (negative parity). By looking at magnification histograms of the convolutions and using χ2 tests to determine the number of observations that would be necessary to distinguish histograms associated with different disk models, we find that, for circular disk models, the microlensing fluctuations are relatively insensitive to all properties of the models except the half-light radius of the disk. Shakura-Sunyaev models are sufficiently well constrained by observed quasar properties that we can estimate the half-light radius at optical wavelengths for a typical quasar. If Shakura-Sunyaev models are appropriate, the half-light radii are very much smaller than the Einstein rings of intervening stars, and the quasar can be reasonably taken to be a point source except in the immediate vicinity of caustic-crossing events.

Discovery of a Fifth Image of the Large Separation Gravitationally Lensed Quasar SDSS J1004+4112

Abstract We report on the discovery of a fifth lensed image in the large separation lensed quasar system SDSS J1004$+$4112. A faint point source located ${0\rlap {.}{}^{\mathrm {\prime \prime }}2}$ from the center of the brightest galaxy in the lensing cluster was detected in images taken with the Advanced Camera for Surveys (ACS) and the Near Infrared Camera and Multi-Object Spectrometer (NICMOS) on the Hubble Space Telescope. The flux ratio between the point source and the brightest lensed component in the ACS image is similar to that in the NICMOS image. The location and brightness of the point source are consistent with lens model predictions for a lensed image. We therefore conclude that the point source is likely to be a fifth lensed image of the source quasar. In addition, the NICMOS image reveals the lensed host galaxy of the source quasar, which can strongly constrain the structure of the lensing critical curves, and thereby the mass distribution of the lensing cluster.

Models of Five Absorption‐Line Systems along the Line of Sight Toward PG 0117+213

We present our investigation into the physical conditions of the gas in five intervening quasar absorption-line systems along the line of sight toward the quasar PG 0117+213, with redshifts of z ¼ 0:57, 0.72, 1.04, 1.32, and 1.34. Photoionization modeling of Hubble Space Telescope, Keck I, and Palomar data, using the code Cloudy, is employed to derive densities and metallicities of the multiple phases of gas required to fit the absorption profile for eachsystem.We discusstheimplicationsofthese models forgalaxy evolution,including theinterpretationof‘‘Civ �

The MIKE/HIRES Lyman limit survey: first results

We present preliminary results of a detailed analysis of the such systems in an effort to accurately characterise this enigmatic and important class of quasar absorption line systems.

Low-redshift quasar absorption-line systems: inside and around galaxies

We present semi-analytic models and Monte-Carlo simulations of QSO Ly for a galaxy halo, in good agreement with observations. Using mock imaging and spectroscopic surveys, selection effects are found to be able to strengthen the anti-correlation between line width and projected distance. The models were also applied to quasar metal absorption lines and more realistic absorption spectra with noise were simulated.

DLAs in simulated galaxies and dust obscuration

We report here and use the results of a set of three-dimensional SPH/Treecode simulations which model the formation and early evolution of disk galaxies, including the generation of heavy elements by star formation, to investigate the effects of dust absorption in quasar absorption line systems. Using a simple prescription for the production of dust, we have compared the column density, zinc abundance, and optical depth properties of our models to the known properties of damped Lyman alpha systems. We find that a significant fraction of our model galaxy disks have a higher column density than any observed DLA system. We are also able to show that such parts of the disk tend to be optically thick, implying that any background quasar would be obscured through much of the disk. This would produce the selection effect against the denser absorption systems thought to be present in observations.

Limits on the transverse velocity of the lensing galaxy in Q2237+0305 from the lack of strong microlensing variability

We present a method for the determination of upper limits on the transverse velocity of the lensing galaxy in the quadruple quasar system Q2237+0305, based on the lack of strong microlensing signatures in the quasar lightcurves. The limits we derive here are based on four months of high quality monitoring data, by comparing the low amplitudes of the lightcurves of the four components with extensive numerical simulations. We make use of the absence of strong variability of the components (especially components B and D) to infer that a flat time interval of such a length is only compatible with an effective transverse velocity of the lensing galaxy of v_bulk <=630 km/s for typical microlenses masses of M_microlens=0.1 M_solar (or v_bulk <=2160 km/s for M_microlens=1.0 M_solar) at the 90% confidence level. This method may be applicable in the future to other systems.

Dust obscuration studies along quasar sight-lines using simulated galaxies

We use the results of a set of three-dimensional SPH-Treecode simulations which model the formation and early evolution of disk galaxies, including the generation of heavy elements by star formation, to investigate the effects of dust absorption in quasar absorption line systems. Using a simple prescription for the production of dust, we have compared the column density, zinc abundance and optical depth properties of our models to the known properties of Damped Lyman alpha systems. We find that a significant fraction of our model galaxy disks have a higher column density than any observed DLA system. We are also able to show that such parts of the disk tend to be optically thick, implying that any background quasar would be obscured through much of the disk. This would produce the selection effect against the denser absorption systems thought to be present in observations.

Knowledge from the time series of quasar radio‐wave flux density

AbstractTime series of radio waves attributable to synchrotron radiation from quasars, that is, extragalactic systems at cosmological distances, were analyzed in an attempt to find an informational structure expressing the evolution and self‐organization of the quasar system. The methods we used were power law analysis of the time series and phase space map analysis of the reconstructed time series.From the power law analysis we found that the dynamical structure of the system is likely to have evolved over the cosmic time scale. From the reconstructed phase space map analysis we obtained patterns similar to attractors in three‐dimensional phase space, which may reflect the system's dynamical structure, and by applying the GP algorithm with the correlation integral we inferred that the dynamical system is of system dimension. © 2003 Wiley Periodicals, Inc. Syst Comp Jpn, 34(10): 56–63, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.10366

Three Emission‐Line Galaxies atz ∼ 2.4

We present Keck near-infrared and WIYN (Wisconsin-Indiana-Yale NOAO) optical photometry of a sample of galaxies detected by near-infrared narrowband imaging in the fields of quasar metal absorption line systems at z ~ 2.4. Wide separations (0.6-1.6 h-1 Mpc) from the quasars indicate that they are not directly responsible for the absorption systems. From the color excess of the galaxies we derived line fluxes, star formation rates, and equivalent widths. The data are consistent with one source having an active nucleus and two sources containing regions of star formation. The blue (R-K) colors for the sources suggest relatively lower dust content. We discuss possible projects using current wide-field infrared instruments, which can cover an order of magnitude greater area with modest allocations of telescope time.

Cosmological deuterium production in non-standard scenarios

It is widely believed that the cosmic baryon density may be obtained by inferring deuterium abundances in low-metallicity quasar absorption line systems. The implicit assumptions which enter this argument are critically assessed. In particular, the production of deuterium in non-standard Big Bang nucleosynthesis scenarios, the putative production of deuterium in astrophysical environments, and the possible destruction of deuterium via non-standard chemical evolution are discussed.

Modelling Neutral Hydrogen Discs of Spiral Galaxies

We present an analytical model of a neutral hydrogen disc in a spiralgalaxy. The gas disc of the spiral galaxy is assumed to have an exponentialsurface density profile and to be ionized by the cosmic ultravioletbackground. To compare with observations, we consider the disc positionangle and inclination angle for a line of sight going through the galaxydisc. The HI column densities depend on the strength of ionizing fieldand disc position and inclination. The model was applied to NGC 3198 andthe results were compared with observational data. The HI disc profileat large disc radii can be tested by further HI observations usingradio telescopes with a larger aperture than the present facilities. This HIdisc model can be used to predict quasar absorption line systems bygalaxy discs if quasar lines of sight go through the discs.

Search for Molecular Gas in the Quasar SDSS 1044−0125 at [CLC][ITAL]z[/ITAL][/CLC] = 5.73

We report upper limits on CO J = 2–1 and J = 5–4 emission from the quasar SDSSp J104433.04-012502.2, at z = 5.73, from observations made with the Berkeley-Illinois-Maryland Association array. Previously reported limits on CO J = 6–5 emission were obtained at z = 5.80, which is now thought to be off by 1%, and the observations likely missed the relevant redshifts for molecular gas. The new 3 σ upper limits on the line luminosities are L(2–1) < 5.1 × 1010 K km s-1 pc2 and L(5–4) < 3.0 × 1010 K km s-1 pc2, assuming 200 km s-1 line width. The CO J = 5–4 observations place an upper limit on warm, dense molecular gas mass comparable to amounts derived for some other high-redshift quasar systems from detections of this line. The limit on CO J = 2–1 emission suggests that excitation bias does not affect this conclusion. In addition, no companion galaxies rich in molecular gas are found in a ∼1.4 Mpc field surrounding the quasar.

The Kinematics of Intermediate-Redshift M[CLC]g[/CLC] [CSC]ii[/CSC] Absorbers

We present 23 quasar absorption-line systems selected by the Mg II ??2796, 2803 doublet with Wr(2796) > 0.3 ? over the redshift range 0.4 ? z ? 1.2. The kinematics and profile morphologies are studied at 6 km s-1 resolution to a 5 ? equivalent width detection threshold of Wr(2796) = 0.015 ?. We are thus sensitive to very weak clouds isolated in velocity. The absorption profiles were segregated into kinematic subsystems, and the properties (velocities, velocity widths, column densities, etc.) were measured directly from the data and by Voigt profile modeling. Most absorbers are characterized by a dominant kinematic subsystem with Wr(2796) > 0.2 ? and velocity spreads ranging from 10 to 50 km s-1 in proportion to the system equivalent width. Additional kinematic subsystems have velocities separations as large as 400 km s-1 relative to the dominant subsystem. The equivalent widths and velocity spreads of these weaker subsystems are anticorrelated with their velocities, and their equivalent width distribution turns down from a power law below Wr(2796) 0.08 ?. These moderate- and high-velocity subsystems are inferred to have sub-Lyman limit H I, and therefore are probably not higher redshift analogs to Galactic high-velocity clouds (HVCs). Weak subsystems are asymmetrically distributed in velocity such that they are either all blueshifted or all redshifted with respect to the dominant subsystem. This implies, that although the kinematic morphologies vary greatly on a case-by-case basis, a given line of sight is apparently probing a well-defined spatial and kinematic structure. We investigate a simple kinematic model that relies on a rotating disk to explain the observed asymmetries. There are systematic differences, or trends, in both the subsystem-to-subsystem velocity clustering and in the overall kinematic morphologies with increasing equivalent width; we discuss how these may provide clues to the observed differential evolution in the equivalent width distribution of Mg II absorbers.

Unified model for quasar absorption line systems

We propose a three component model consisting of minihalos and galactic halos with embedded thin discs for absorbers producing all the observed classes of intervening quasar absorption line systems. We show that this model, based on CDM cosmology, can explain most of the observed statistical distributions of various types of absorption systems. Use of the Schechter luminosity function for absorbers, on the other hand, is consistent with the observations only if the number of galaxies was larger in the past and reduced with time due to mergers. A strong chemical evolution in the halos of galaxies is indicated by the observed properties of CIV lines. We discuss our results in the light of the recent observations of the absorption line systems.