Quasar Environments Research Articles

The Application of the Study of Galaxies Associated With Quasars to Observational Cosmology

CCD direct imaging of fields around quasars is used as a method for locating galaxy clusters and groups associated with quasars. Average galaxy counts in the sky obtained from control fields are used to correct for background galaxies in the quasar fields. This correction allows one to derive the luminosity function (LF) of the associated galaxies at the redshifts of the quasars. It is demonstrated that using the derived LF and average galaxy count data, self-consistent models of the evolution of the LF and galaxy counts can be obtained. Current data are best fitted, with a large uncertainty, by a qo between 0.0 and 0.5 and an evolution in M* of −0.9±0.5 mag. It is found that the average environment of radio-loud quasars at z∼0.6 is about three times richer in galaxies than that of quasars at z∼0.4.

Surveys of fields around quasars. III - Intermediate-redshift quasars: Catalog and background galaxy counts

Images in Gunn r (6500 + or - 450 A) and i (8200 + or - 600 A) of fields around 31 bright quasars have been obtained for the purpose of studying the global environments of quasars. Procedures for object identification, aperture photometry, and object classification are discussed. A catalog of the positional offsets from the quasar and the magnitudes and classifications of the detected objects is presented. In addition, selected control fields positioned 1 deg north of some quasars, for the purpose of background galaxy counting, were also observed. Despite the small area covered, the average background galaxy counts obtained agree well with previous results. For r over 21 mag, the distributions of counts in the 27 control fields are found to deviate significantly from Poisson statistics. 28 references.

Galaxy correlations at high redshift and the environment of quasars

Lorsque les deux quasars d'une paire sont proches, des raies d'absorption peuvent etre observees dans le spectre de l'objet le plus eloigne, a un deplacement vers le rouge qui correspond a celui de l'objet le plus proche. Cela indique la presence d'une galaxie dans le meme amas (et contenant) le quasar proche. On etudie la probabilite de ce phenomene

An imaging survey of fields around quasars. II - The association of galaxies with quasars

view Abstract Citations (164) References (33) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS An imaging survey of fields around quasars. II. The association of galaxies with quasars. Yee, H. K. C. ; Green, R. F. Abstract Images centered on 108 quasars with redshifts between 0.05 and 2.05 were obtained using the direct-SIT camera on the Palomar 1.52 m telescope. This paper presents the analyzed data without a priori assumptions about the nature of quasar redshifts and shows that the results are consistent with the hypothesis that quasars are associated with galaxies at the cosmological distances implied by the quasar redshifts. By assuming that quasars are at their cosmological redshift distances, some of the physical properties of the groups and clusters that are apparently associated with the quasars are derived. Marginally significant differences were found between the environments of radio-loud and radio-quiet quasars. Publication: The Astrophysical Journal Pub Date: May 1984 DOI: 10.1086/161969 Bibcode: 1984ApJ...280...79Y Keywords: Galactic Clusters; Quasars; Red Shift; Covariance; Density Distribution; Luminosity; Magnitude; Radial Distribution; Astrophysics full text sources ADS | data products SIMBAD (1) NED (1) Related Materials (3) Part 1: 1984ApJS...54..495G Part 3: 1986ApJS...62..681Y Part 4: 1987ApJ...319...28Y

An imaging survey of fields around quasars. I - A catalog

view Abstract Citations (45) References (18) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS An imaging survey of fields around quasars. I. A catalog Green, R. F. ; Yee, H. K. C. Abstract Images in Gunn r (6500 + or - 450 A) of fields around 108 bright quasars have been obtained using the SIT-vidicon camera on the Palomar 1.52 m telescope for the purpose of studying the global environments of quasars. The sample consists of quasars from complete optical and radio surveys, with redshifts ranging from 0.05 to over 2.0. A catalog of the positional offsets from the quasar, the magnitudes, and the classifications (into stars or galaxies) of the detected objects is presented. In addition, control fields 1 deg N of each quasar, for the purpose of background galaxy counting, were also observed. The background galaxy counts derived from the control fields, covering a total area of 0.226 sq deg, are in good agreement with the counts obtained by Kron and Sebok. Publication: The Astrophysical Journal Supplement Series Pub Date: April 1984 DOI: 10.1086/190941 Bibcode: 1984ApJS...54..495G Keywords: Astronomical Catalogs; Astronomical Coordinates; Astronomical Photography; Galactic Clusters; Quasars; Red Shift; Intergalactic Media; Magnitude; Astronomy full text sources ADS | data products SIMBAD (106) NED (83) Related Materials (3) Part 2: 1984ApJ...280...79Y Part 3: 1986ApJS...62..681Y Part 4: 1987ApJ...319...28Y

Quasar number density evolution

A simple model of quasar number density evolution is presented based on the occurrence of quasar-like radio galaxies (i.e., strong optical emission lines and type 2 radio morphology) exclusively in regions of low galaxy and intergalactic medium (IGM) density. This suggests a limit for the IGM density of 10 to the -4th (+ or - 1) per cu cm below which quasars are allowed to form and above which they are not allowed. In the recent past (z not greater than 1), the inferred quasar environments are the outskirts of clusters and near the centers of groups of galaxies. However, models of rich cluster evolution consistent with current X-ray observations predict gas densities of less than 10 to the -4th per cu cm in cluster cores in the more distant past (z between 1 and 5). This suggests that quasars were allowed to form in the cores of rich clusters at those epochs, which explains both the rich absorption spectra of high-redshift quasars and the absence of clusters surrounding quasars at lower redshift.