Sloan Digital Sky Survey QSO Research Articles

CALIBRATING C-IV-BASED BLACK HOLE MASS ESTIMATORS

We present the single-epoch black hole mass estimators based on the CIV (1549 A) broad emission line, using the updated sample of the reverberation-mapped AGNs and high-quality UV spectra. By performing multi-component spectral fitting analysis, we measure the CIV line widths (FWHM_CIV) and line dispersion (sigma_CIV) and the continuum luminosity at 1350 A (L_1350) to calibrate the CIV-based mass estimators. By comparing with the Hbeta reverberation-based masses, we provide new mass estimators with the best-fit relationships, i.e., M_BH \propto L_1350 ^ (0.50+-0.07) sigma_CIV ^2 and M_BH \propto L_1350 ^ (0.52+-0.09) FWHM_CIV ^ (0.56+-0.48). The new CIV-based mass estimators show significant mass-dependent systematic difference compared to the estimators commonly used in the literature. Using the published Sloan Digital Sky Survey QSO catalog, we show that the black hole mass of high-redshift QSOs decreases on average by ~0.25 dex if our recipe is adopted.

QSO-LRG two-point cross-correlation function and redshift-space distortions

We have measured the bias of QSOs as a function of QSO luminosity at xed redshift (z < 1) by cross-correlating them with luminous red galaxies (LRGs) in the same spatial volume, hence breaking the degeneracy between QSO luminosity and redshift. We use three QSO samples from 2SLAQ, 2QZ and Sloan Digital Sky Survey (SDSS) covering a QSO absolute magnitude range, -24.5 <M < -21.5, and cross-correlate them with 2SLAQ (z ≈ 0.5) and AAOmega (z ≈ 0.7) photometric and spectroscopic LRGs in the same redshift ranges. The spectroscopic QSO samples, in the spectroscopic LRG areas, contain up to 700 QSOs and in photometric LRG areas up to 7000 QSOs. The 2D and 3D cross-clustering measurements are generally in good agreement. Our (2SLAQ) QSO-LRG clustering amplitude (r = 6.98 ± 0.6 h Mpc) as measured from the semiprojected cross-correlation function appears similar to the (2SLAQ) LRG-LRG autocorrelation amplitude (r = 7.45 ± 0.35 h Mpc) and both are higher than the (2QZ + 2SLAQ) QSO-QSO amplitude (r ≈ 5.0 h Mpc). Our measurements show remarkably little QSO-LRG cross-clustering dependence on QSO luminosity. This result is unexpected on the basis of simple high-peak biasing models, where more luminous QSOs are assumed to occupy rarer and so more clustered high-mass peaks. Assuming a standard ΛCDM model and values for b measured from LRG autocorrelation analyses, from the spectroscopic samples at z ≈ 0.55 we nd b = 2.3 ± 0.5 at M ≈-24 and b = 1.6 ± 0.3 at M ≈-22. Averaging over all the spectroscopic and photometric samples, we nd an average value of b = 1.8 ± 0.1 at z ≈ 0.6 and M ≈-23. The implied dark matter halo mass inhabited by QSOs is ≈ 10 h M, again approximately independent of QSO luminosity. We have also made a z-space distortion analysis of the QSO-LRG cross-clustering at z ≈ 0.55. The velocity dispersion tted to QSO-LRG cross-correlation, ξ (σ, π), at ±600 km s is close to that expected given the larger QSO redshift errors. The dynamical infall result for the combined 2SLAQ, 2QZ and SDSS QSO sample gives β = 0.23 ± 0.15 which implies b = 3.2 ± 2.1, assuming the standard cosmological model. Although noisier, this latter value is consistent with the value of b = 1.9 ± 0.2 obtained from the amplitude of the cross-correlation function in the same redshift range. © 2009 The Authors. Journal compilation

The 2df SDSS LRG and QSO survey: evolution of the luminosity function of luminous red galaxies toz= 0.6

We present new measurements of the luminosity function (LF) of luminous red galaxies (LRGs) from the Sloan Digital Sky Survey (SDSS) and the 2dF SDSS LRG and Quasar (2SLAQ) survey. We have carefully quantified, and corrected for, uncertainties in the K and evolutionary corrections, differences in the colour selection methods, and the effects of photometric errors, thus ensuring we are studying the same galaxy population in both surveys. Using a limited subset of 6326 SDSS LRGs (with 0.17 < z < 0.24) and 1725 2SLAQ LRGs (with 0.5 < z < 0.6), for which the matching colour selection is most reliable, we find no evidence for any additional evolution in the LRG LF, over this redshift range, beyond that expected from a simple passive evolution model. This lack of additional evolution is quantified using the comoving luminosity density of SDSS and 2SLAQ LRGs, brighter than M0.2r − 5 log h0.7 = −22.5, which are 2.51 ± 0.03 × 10−7 L Mpc−3 and 2.44 ± 0.15 × 10−7 L Mpc−3, respectively (<10 per cent uncertainty). We compare our LFs to the COMBO-17 data and find excellent agreement over the same redshift range. Together, these surveys show no evidence for additional evolution (beyond passive) in the LF of LRGs brighter than M0.2r − 5 log h0.7 = −21 (or brighter than L*). We test our SDSS and 2SLAQ LFs against a simple ‘dry merger’ model for the evolution of massive red galaxies and find that at least half of the LRGs at z 0.2 must already have been well assembled (with more than half their stellar mass) by z 0.6. This limit is barely consistent with recent results from semi-analytical models of galaxy evolution.

Statistical Cluster-QSO Weak Lensing in the Sloan Digital Sky Survey

We investigate the cross-correlation between galaxy clusters and QSOs using Sloan Digital Sky Survey (SDSS) DR4 ~5000 deg2 data. With photometric redshifts of galaxies, we select galaxy clusters based on the local projected densities of LRGs brighter than Mr' = −22. The QSOs are from the main sample of SDSS QSO spectroscopic survey to i' = 19. A significant positive correlation is found between the clusters and QSOs. Under the assumption that the signal is caused by gravitational lensing, we fit the signal with singular isothermal sphere (SIS) model and NFW profile halo model. The velocity dispersion σv = 766 km s−1 is derived for the best-fit of SIS model. Best-fit for the NFW model requires the dark matter halo mass within 1.5 h−1 Mpc to be 4.6×1014 h−1 M⊙. The mass parameter Ωcl of the cluster sample is deduced as 0.077 with the SIS model and 0.083 with the NFW model. Our results of Ωcl are smaller than those given by Croom & Shanks and by Myers et al.

The Optical-Infrared Colors of CORALS QSOs: Searching for Dust Reddening Associated with High-Redshift Damped Lyα Systems

The presence of dust in quasar absorbers, such as damped Lyα (DLA) systems, may cause the background QSO to appear reddened. We investigate the extent of this potential reddening by comparing the optical-to-infrared colors of QSOs with and without intervening absorbers. Our QSO sample is based on the Complete Optical and Radio Absorption Line System (CORALS) survey of Ellison and coworkers. The CORALS data set consists of 66 radio-selected QSOs at zem ≥ 2.2 with complete optical identifications. We have obtained near-simultaneous B- and K-band magnitudes for a subset of the CORALS sample and supplemented our observations with further measurements published in the literature. In total, we have B - K colors for 42 of the 66 QSOs, of which 14 have intervening DLA systems. To account for redshift-related color changes, the B - K colors are normalized using the Sloan Digital Sky Survey QSO composite. The mean normalized B - K color of the DLA subsample is +0.12, whereas the mean for the no-DLA sample is -0.10; both distributions have rms scatters of ~0.5. Neither a Student's t-test nor a Kolmogorov-Smirnov test indicate that there is any significant difference between the two color distributions. Based on simulations that redden the colors of QSOs with intervening DLA systems, we determine a reddening limit that corresponds to E(B - V) < 0.04 (SMC-like extinction) at 99% confidence (3 σ), assuming that E(B - V) is the same for all DLA systems. Finally, we do not find any general correlation between absorber properties (such as [Fe/Zn] or neutral hydrogen column density) and B - K color. The two reddest QSOs with DLA systems in our sample have H I column densities that differ from each other by an order of magnitude and moderate gas-to-dust ratios as inferred from chemical abundances. One of these two QSOs shows evidence for strong associated absorption from X-ray observations, an alternative explanation for its very red color. We conclude that the presence of intervening galaxies causes a minimal reddening of the background QSO.

MgiiAbsorption Systems in Sloan Digital Sky Survey QSO Spectra

We present the results of a Mg II λλ2796, 2803 absorption-line survey using QSO spectra from the Sloan Digital Sky Survey (SDSS) Early Data Release. Over 1300 doublets with rest equivalent widths greater than 0.3 Å and redshifts 0.366 ≤ z ≤ 2.269 were identified and measured. We find that the λ2796 rest equivalent width (W) distribution is described very well by an exponential function ∂N/∂W = e, with N* = 1.187 ± 0.052 and W* = 0.702 ± 0.017 Å. Previously reported power-law fits drastically overpredict the number of strong lines. Extrapolating our exponential fit underpredicts the number of W ≤ 0.3 Å systems, indicating a transition in ∂N/∂W near W ≃ 0.3 Å. A combination of two exponentials reproduces the observed distribution well, suggesting that Mg II absorbers are the superposition of at least two physically distinct populations of absorbing clouds. We also derive a new redshift parameterization for the number density of W ≥ 0.3 Å lines: N* = 1.001 ± 0.132 (1 + z)0.226±0.170 and W* = 0.443 ± 0.032 (1 + z)0.634±0.097 Å. We find that the distribution steepens with decreasing redshift, with W* decreasing from 0.80 ± 0.04 Å at z = 1.6 to 0.59 ± 0.02 Å at z = 0.7. The incidence of moderately strong (0.4 Å ≲ W ≲ 2 Å) Mg II λ2796 lines does not show evidence for evolution with redshift. However, lines stronger than ≈2 Å show a decrease relative to the no-evolution prediction with decreasing redshift for z ≲ 1. The evolution is stronger for increasingly stronger lines. Since W0 in saturated absorption lines is an indicator of the velocity spread of the absorbing clouds, we interpret this as an evolution in the kinematic properties of galaxies from moderate to low redshift. Monte Carlo simulations do not reveal any strong systematic effects or biases in our results. While more recent SDSS QSO spectra offer the opportunity to increase the Mg II absorber sample by another order of magnitude, systematic errors in line identification and measurement will begin to dominate in the determination of absorber property statistics.

The Sloan Digital Sky Survey QSO absorption line catalogue

The spectra of the Sloan Digital Sky Survey (SDSS) are being used to construct a catalogue of QSO absorption lines, for use in studies of abundances, relevant radiation fields, number counts as a function of redshift, and other matters, including the evolution of these parameters. The catalogue includes intervening, associated, and BAL absorbers, in order to allow a clearer definition of the relationships between these three classes. We describe the motivation for and the data products of the project to build the SDSS QSO absorption line catalogue.

Intrinsic Absorption in Radio‐selected Quasars

Moderate resolution spectra have been recorded for a sample of radio-selected QSOs (z ~ 2.5) discovered in the Faint Images of the Radio Sky at Twenty centimeters (FIRST) VLA survey. This work is motivated by the study of a heterogeneous set of QSO absorption line spectra that showed that as many as 36% of the absorbers normally thought to be intergalactic are correlated with physical properties of the background QSO, including the radio source spectral index. Spectra were taken for 24 newly discovered quasars in order to test this finding on a more homogeneous data set. The spectra have been searched for the most frequently observed absorption lines. The absorption line properties are compared to the radio properties of the quasars. The primary results are summarized as follows: (1) an excess of C IV absorbers in flat-spectrum quasars as compared to steep-spectrum quasars is confirmed (based on a total sample of 165 systems), (2) a small excess of high-velocity C IV absorbers is seen in radio-quiet QSOs as compared to radio-loud quasars, and (3) the Sloan Digital Sky Survey QSO spectra will allow for the detection of a high-velocity, narrow, intrinsic population of absorbers that is as small as 7% of the C IV absorber population in QSOs at z ~ 2.5.