No abstract

We present the fifth edition of the Sloan Digital Sky Survey (SDSS) Quasar Catalog, which is based upon the SDSS Seventh Data Release. The catalog, which contains 105,783 spectroscopically confirmed quasars, represents the conclusion of the SDSS-I and SDSS-II quasar survey. The catalog consists of the SDSS objects that have luminosities larger than M i = −22.0 (in a cosmology with H 0 = 70 km s −1 Mpc −1 , Ω M = 0.3, and Ω Λ = 0.7), have at least one emission line with FWHM larger than 1000 km s −1 or have interesting/complex absorption features, are fainter than i ≈ 15.0, and have highly reliable redshifts. The catalog covers an area of ≈ 9380 deg 2 . The quasar redshifts range from 0.065 to 5.46, with a median value of 1.49; the catalog includes 1248 quasars at redshifts greater than four, of which 56 are at redshifts greater than five. The catalog contains 9210 quasars with i < 18; slightly over half of the entries have i < 19. For each object the catalog presents positions accurate to better than 0.1 ′′ rms per coordinate, five-band (ugriz) CCD-based photometry with typical accuracy of 0.03 mag, and information on the morphology and selection method. The catalog also contains radio, near-infrared, and X-ray emission properties of the quasars, when available, from other large-area surveys. The calibrated digital spectra cover the wavelength region 3800-9200Å at a spectral resolution of ≃ 2000; the spectra can be retrieved from the SDSS public database using the information provided in the catalog. Over 96% of the objects in the catalog were discovered by the SDSS. We also include a supplemental list of an additional 207 quasars with SDSS spectra whose archive photometric information is incomplete.

Recent studies of black holes in the nuclei of both active and normal galaxies have yielded relationships that permit a physical interpretation of the principal components of the spectra of QSOs. It is shown that principal component (or eigenvector) 1 (PC1) is driven predominantly by and prin-L /L Edd , cipal component 2 (PC2) is driven by accretion rate. This results in a PC2 versus PC1 diagram in which lines of constant black hole mass are diagonal. Using a sample consisting of the low-redshift PG objects supplemented by 75 radio-loud QSOs, it is shown that such a diagram e †ectively distinguishes radioloud from radio-quiet objects and demonstrates that both narrow-line Seyfert 1 galaxies and broad absorption line QSOs lie at the high extreme, although these two types of objects are well L /L Edd separated in the PC2 direction. A simple picture that ties together physical parameters (black hole mass and Eddington ratio) and classiÐcation of active galactic nuclei is presented. Based on the location of core-dominated and lobe-dominated radio-loud QSOs, orientation can be modeled as a third parameter in this scheme, implying an enhancement in the radio Ñux of core-dominated objects.

We present ground-based optical photometric monitoring data for NGC 5548, part of an extended multiwavelength reverberation mapping campaign. The light curves have nearly daily cadence from 2014 January to July in nine filters (BVRI and ugriz). Combined with ultraviolet data from the Hubble Space Telescope and Swift, we confirm significant time delays between the continuum bands as a function of wavelength, extending the wavelength coverage from 1158 Å to the z band (∼ 9160 Å). We find that the lags at wavelengths longer than the V band are equal to or greater than the lags of high-ionization-state emission lines (such as He II λ1640 and λ4686), suggesting that the continuum-emitting source is of a physical size comparable to the inner broad-line region (BLR). The trend of lag with wavelength is broadly consistent with the prediction for continuum reprocessing by an accretion disk with τ ∝ λ 4/3 . However, the lags also imply a disk radius that is 3 times larger than the prediction from standard thin-disk theory, assuming that the bolometric luminosity is 10% of the Eddington luminosity (L = 0.1L Edd ). Using optical spectra from the Large Binocular Telescope, we estimate the bias of the interband continuum lags due to BLR emission observed in the filters. We find that the bias for filters with high levels of BLR contamination (∼ 20%) can be important for the shortest continuum lags, and likely has a significant impact on the u and U bands owing to Balmer continuum emission.

We have carried out a systematic search for close supermassive black hole binaries (with sub-parsec separations) among z < ∼ 0.7 quasars observed spectroscopically in the Sloan Digital Sky Survey. Such binaries are predicted by models of supermassive black hole and host galaxy co-evolution, therefore their census and population properties constitute an important test of these models. Our working hypothesis is that one of the two black holes accretes at a much higher rate than the other and carries with it the only broad-emission line region of the system, making the system analogous to a single-lined spectroscopic binary star. Accordingly, we used an automatic technique based on spectroscopic principal component analysis to search for broad Hβ emission lines that are displaced from the rest-frame of the quasar by |∆v| > ∼ 1, 000 km s −1 (corresponding to binary periods and separations of P ∼ few × 100 yr and a ∼ few × 0.1 pc, respectively, for masses ∼ 10 8 M ⊙ ). This method can also yield candidates for rapidly recoiling black holes since their spectroscopic signature is similar. Our search yielded 88 candidates, several of which were previously identified and discussed in the literature. The widths of the broad Hβ lines are typical among quasars but the shifts are extreme. We found a correlation between the peak offset and skewness of the broad Hβ profiles (there is an extended wing on the opposite side of the profile from the shifted peak), which suggests that the profiles we have selected share a common physical explanation. The general properties of the narrow emission lines are typical of quasars. We carried out followup spectroscopic observations of 68 objects to search for changes in the peak velocities of the Hβ lines (the time interval in the observer's frame between the original and new observations is 1-10 yr and 5.7-10.0 yr in 2/3 of the cases). We measured statistically significant changes (at 99% confidence) in 14 objects, with resulting accelerations between −120 and +120 km s −1 yr −1 . The above results, taken at face value, are broadly consistent with predictions for the number of close supermassive binaries in the Sloan Digital Sky Survey quasar sample. However, such a comparison is complicated by several theoretical and observational uncertainties, such as the fact that the observable we employ to select objects depends on a combination of several degenerate intrinsic parameters of a binary. We emphasize that interpretation of the offset broad emission lines as signatures of supermassive binaries is subject to many significant caveats. Many more followup observations over a long temporal baseline are needed to characterize the variability pattern of the broad lines and test that this pattern is indeed consistent with orbital motion. The possibility that some of the objects in this sample are rapidly recoiling black holes remains open as the available data do not provide strong constraints for this scenario.