We select a sample of ∼ 4200 traditionally defined broad absorption line quasars (BALQs) from the Fifth Data Release quasar catalog of the Sloan Digital Sky Survey. For a statistically homogeneous quasar sample with 1.7 ≤ z ≤ 4.2, the BAL quasar fraction is ∼ 14% and is almost constant with redshift. We measure the auto-correlation of non-BAL quasars (nonBALQs) and the cross-correlation of BALQ...

Quasars are among the most luminous objects in the universe , and they can be studied in detail up to the highest known redshift. Assuming that the gas associated with quasars is closely related to the interstellar medium of the host galaxy, quasars can be used as tracer of the star formation history in the early universe. We have observed a small sample of quasars at redshifts 3 ∼ < z ∼ < 5 an...

We have quantified the galaxy environments around a sample of 0.5 ≤ z ≤ 0.8 radioquiet quasars using the amplitude of the spatial galaxy–quasar correlation function, Bgq. The quasars exist in a wide variety of environments, some sources are located in clusters as rich as Abell class 1–2 clusters, whereas others exist in environments comparable to the field. We find that on average, the quasars ...

Observations with the Wide-Field/Planetary Camera-2 of the Hubble Space T elescope are presented for three radio-loud quasars : 3C 48 (z\ 0.367), B2 1425]267 (z\ 0.366), and 3C 345 (z\ 0.594). All three quasars have luminous (D4 ] L*) galaxies as hosts, which are either elliptical (B2 1425]267 and 3C345) or interacting (3C 48), and all hosts are 0.5È1.0 mag bluer in V [I than other galaxies wit...

Quasars of high redshift may be ejected from a nearby active galaxy of low redshift. This physical association then leads to the suggestion that the redshifts of quasars are not really an indication of their distances. In this investigation, it is argued that the high redshift can be due to the gravitational redshift as an intrinsic redshift. Based on the proposed local-ether theory, this intri...

We have cross-correlated the SDSS DR3 Schneider et al. (2005) quasar catalog with the XMMNewton archive. Color and redshift selections (g − r ≥ 0.5 and 0.9 < z < 2.1) result in a sample of 17 red, moderate redshift quasars. The redshift selection minimizes possible contamination due to host galaxy emission and Lyα forest absorption. Both optical and X-ray information are required to distinguish...

It is currently unknown whether the Universe was reionized by quasars or stars at z ∼ > 5. We point out that quasars can be best distinguished from stellar systems by their X-ray emission. Based on a simple hierarchical CDM model, we predict the number counts and X-ray fluxes of quasars at high redshifts. The model is consistent with available data on the luminosity function of high-redshift qu...

We have undertaken deep optical imaging observations of three 6.2 < z < 6.5 quasar fields in the i and z filters. These data are used to search for foreground galaxies which are gravitationally lensing the quasars and distant galaxies physically associated with the quasars. Foreground galaxies are found closer than 5 from the lines-of-sight of two of the three quasars. However, the faintness of...

The intrinsic fraction of broad absorption line quasars (BALQSOs) is important in constraining geometric and evolutionary models of quasars. We present the fraction of BALQSOs in 2MASS detected quasars within the SDSS DR3 sample in the redshift range of 1.7 ≤ z ≤ 4.38. The fraction of BALQSOs is 40.4 −3.3% in the 2MASS 99% database Ks band completeness sample, and 38.5 +1.7 −1.7% in the larger ...

We have constructed a sample of quasar candidates by comparing the FIRST radio survey with the 16 deg Deeprange I-band survey carried out by Postman et al. (1998, 2002). Spectroscopic followup of this magnitude-limited sample (I < 20.5, Fν(20cm) > 1 mJy) has revealed 35 quasars, all but two of which are reported here for the first time. This sample contains some unusual broad absorption line qu...