Large groups of quasars in an ultra-violet excess survey

Details Large groups of quasars in an ultra-violet excess survey Large groups of quasars in an ultra-violet excess survey

Oct 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999phdt..........n&link_type=abstract

PhD Thesis, University of Central Lancashire

Mathematics

Probability

7

Quasars, Survey, Large-Scale Structure

Scientific paper

This thesis describes the objectives, design, construction and analysis of the Chile-UK Quasar Survey, a new wide-field spectroscopic redshift survey of ultraviolet-excess quasar candidates. The main objectives of the survey are the construction of a large, homogeneous catalogue of quasars with redshifts 0.4<= z<=2.2, and the use of the catalogue to investigate the lss\ of the early Universe, particularly at large scales ( ~100hmompc). The survey covers 140degrsq, with a 10degr*Edegr programme area centred at 10rah40ram, +5degr00arcmin, and a 6fdg3x6fdg3 control area centred at 11rah14ram, -29degr00arcmin (B1950 coordinates). Quasar candidates have been selected on 16<=bj<=20 and (uj-bj)<=-0.3 from UKST\ photographic plates in the U and J bands digitized on the SuperCOSMOS machine at the ROE. The methods developed for astrometric and photometric calibration of the SUPCOS\ data are described in detail. Positional uncertainties of Deltar=0.69 arcsec s\ and magnitude uncertainties of Deltabj=0.10 mag and Deltauj=0.12 mag are achieved across the whole survey area. A function relating positional uncertainty to the efficiency of light collection for spectrographs with optical-fibre input is derived and used to show that the efficiency for this survey is >80 per cent. Survey observations using a multi-object spectrograph with optical-fibre input on the 2.5-m du Pont telescope at the Las Campanas Observatory in Chile are reported. Spectra of 4588 candidates from 54degrsq\ of the survey area have been obtained in 12 nights of observations conducted in 1996 March, 1997 March and 1998 May. Of these spectra, 3134 have been analysed, resulting in the identification of 320 quasars with redshifts in the range 0.228<={z}<=2.768, and 93 narrow emission-line galaxies with redsh! ifts in the range 0.015<={z}<=0.397. The distributions of the quasar and NELG samples as functions of position, redshift, apparent magnitude, colour and luminosity are described in detail. It is argued that the quasar sample is highly homogeneous and at least 70 per cent complete. Identifications of objects without emission lines are discussed. A minimal spanning tree analysis of a homogeneous sample of 227 quasars drawn from the survey programme area catalogue identifies two large groups of quasars with high statistical significance. The first group contains 6 quasars with median redshift z = 1.236 and mean separation 26+/-9hmompc. The null hypothesis that the quasars in this group are distributed randomly is rejected by the (m, simga) test of Graham et al. (1995) at the 0.0011 level, and the probability that this is a random significant event is 5 per cent. The shape of the group suggests a single filament with a length of ~110hmompc\ and a width of ~15hmompc. This group coincides with the core of the Clowes & Campusano (1991) group, the reality of which is confirmed by this independent survey. The second group is a new discovery. It contains 13 quasars with median redshift z = 1.507 and mean separation 32+/-7hmompc. The msig\ test finds that this group is significant at the 0.0020 level, and the upper limit on probability that this is a random significant event is 13 per cent. The shape of the second group resembles three intersecting filaments with an overall size of ~150x80x85hmtmpct, making it one of the largest structures in the Universe found so far. The use of measures of the Civ\ wave{1549} broad emission line to determine the intrinsic luminosity of quasars is investigated, using spectra from a luminosity-limited sample of survey quasars. The observational evidence and theoretical basis for a power-law correlation between luminosity and equivalent width (the Baldwin Effect) are reviewed. A model that predicts a power-law correlation between luminosity and the velocity width of broad emission lines is described. The Baldwin Effect correlation is detected at the 2.4-sigma level. A positive slope for a luminosity-velocity width correlation is detected in agreement with the proposed model but at lower significance.

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