Quasi-stellar object (QSO) spectral templates are important both to QSO physics and for investigations that use QSOs as probes of intervening gas and dust. However, combinations of various QSO samples obtained at different times and with different instruments so as to expand a composite and to cover a wider rest frame wavelength region may create systematic effects, and the contribution from QSO hosts may contaminate the composite. We have constructed a composite spectrum from luminous blue QSOs at 1<z<2.1 selected from the Sloan Digital Sky Survey (SDSS). The observations with X-shooter simultaneously cover ultraviolet (UV) to near-infrared (NIR) light, which ensures that the composite spectrum covers the full rest-frame range from Ly{beta} to 11350{AA} without any significant host contamination. Assuming a power-law continuum for the composite we find a spectral slope of {alpha}{lambda}=1.70+/-0.01, which is steeper than previously found in the literature. We attribute the differences to our broader spectral wavelength coverage, which allows us to effectively avoid fitting any regions that are affected either by strong QSO emissions lines (e.g., Balmer lines and complex [FeII] blends) or by intrinsic host galaxy emission. Finally, we demonstrate the application of the QSO composite spectrum for evaluating the reddening in other QSOs.
We present the Bright Quasar Survey (BQS) consisting of 114 objects to an average limiting magnitude B=16.16 over an area of 10714{deg}^2^. There are 92 quasars with M_B_<-23 in the sample. We use the BQS and complete samples from published surveys to derive models of the statistical evolution of quasars. The increase of space density with redshift depends strongly on absolute luminosity, being close to zero for low-luminosity quasars. Detailed predictions are given for the distribution of redshifts and magnitudes and for the total counts based on the evolution models.
We present a sample of 8498 quasars with both Sloan Digital Sky Survey (SDSS) ugriz optical and United Kingdom Infrared Telescope (UKIRT) Infrared Deep Sky Survey (UKIDSS) YJHK near-infrared (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 analysing the quasar colours, we propose an empirical criterion in the Y-K versus g-z colour-colour diagram to separate stars and quasars with redshift z<4, and two other criteria for selecting high-redshift quasars. Using the SDSS-UKIDSS colour-z relations, we estimate the photometric redshifts of 8498 SDSS-UKIDSS quasars, and find that 85.0 per cent of them are consistent with the spectroscopic redshifts within |{Delta}z|<0.2, which leads to a significant increase of the photometric redshift accuracy from that based on the SDSS colour-z relations only. As two tests, we compare our colour-selection criterion with a small UKIDSS/EDR quasar/star sample and a sample of 4671 variable sources in the SDSS Stripe 82 region with both SDSS and UKIDSS data. We find that they can be clearly divided into two classes (quasars and stars) by our criterion in the Y-K versus g-z plot.
A new catalog of 8382 close quasar-galaxy pairs is presented. The catalog was composed using published catalogued quasars and active galactic nuclei containing 11358 objects, as well as the LEDA catalog of galaxies, which contains on the order of 100000 objects.
A sample of quasars is selected from a 10-yr sequence of 30 UK Schmidt plates. Luminosity functions are derived in several redshift intervals, which in each case show a featureless power-law rise towards low luminosities. There is no sigh of the 'break' found in the recent UVX sample of Boyle, Shanks & Peterson. It is suggested that reasons for the disagreement are connected with biases in the selection of the UVX sample. The question of the nature of quasar evolution appears to be still unresolved.
We determine the number counts and z=0-5 luminosity function for a well-defined, homogeneous sample of quasars from the Sloan Digital Sky Survey (SDSS). We conservatively define the most uniform statistical sample possible, consisting of 15343 quasars within an effective area of 1622{deg}^2^ that was derived from a parent sample of 46420 spectroscopically confirmed broad-line quasars in the 5282{deg}^2^ of imaging data from SDSS Data Release 3. The sample extends from i=15 to 19.1 at z<~3 and to i=20.2 for z>~3.
The hosts of luminous z~2 quasars evolve into today's massive elliptical galaxies. Current theories predict that the circumgalactic medium (CGM) of these massive, dark matter halos (M_DM_~10^12.5^M_{sun}_) should be dominated by a T~10^7^K virialized plasma. We test this hypothesis with observations of 74 close-projected quasar pairs, using spectra of the background QSO to characterize the CGM of the foreground one. Surprisingly, our measurements reveal a cool (T~10^4^K), massive (M_CGM_>10^10^M_{sun}_), and metal-enriched (Z>~0.1Z_{sun}_) medium extending to at least the expected virial radius (r_vir_=160kpc). Furthermore, we conservatively estimate that the quasar CGM has a 64^+6^_-7_% covering fraction of optically thick gas (N_HI_>10^17.2^/cm^2^) within r_vir_; this covering factor is twice that of the contemporaneous Lyman break galaxy population. This unexpected reservoir of cool gas is rarely detected "down-the-barrel" to quasars, and hence it is likely that our background sight lines intercept gas that is shadowed from the quasar ionizing radiation by the same obscuring medium often invoked in models of active galactic nucleus unification. Because the high-z halos inhabited by quasars predate modern groups and clusters, these observations are also relevant to the formation and enrichment history of the intragroup/intracluster medium.
Table 2 contains optical (V) polarimetric measurements for 42 optically selected QSOs including 29 broad absorption line QSOs. Table 3 contains a series of spectral indices characterizing the broad absorption line QSOs.
This catalogue is an update of the previous versions. The recent release of the final release of the 2dF quasar catalogue and of the first part of the SLOAN catalogue, almost doubling the number of known QSOs, led us to prepare an updated version of our Catalogue of quasars and active nuclei, which now contains 48921 quasars, 876 BL Lac objects and 15069 active galaxies (including 11777 Seyfert 1). Like the tenth edition, it includes position and redshift as well as photometry (U, B, V) and 6 and 11 cm flux densities when available. The present edition this catalogue contains the quasars with measured redshift known prior to August 1st, 2003.
