Objective-prism and slit-spectra redshifts in a study of the distribution of galaxies

[摘要] A thorough and detailed investigation into the accuracy,reliability and consistency of the objective-prism redshift techniquewith changes in plate material, measuring machine and reductiontechniques has been undertaken. Providing that the limitations of theprocedures involved are appreciated, useful 3-D information, accurateto Z~±0.01, for large numbers of faint galaxies may be obtained fromsingle UKST fields. A surface brightness correction has enabled thetechnique to be extended to galaxies as bright as bj ~15.8. Thevalidity of the results were confirmed by external calibration withslit-spectra. The slit-spectra results obtained have more thandoubled the size of the calibration sample available and have furthervindicated the applicability of the technique.Analysis of the 107 slit-spectra redshifts determined revealedthe existence of considerable structure in the field studied, withsignificant density enhancements and voids being apparent. Thisstructure has been confirmed on larger scales and to greater depthswith the subsequent analysis of ~1,500 objective-prism redshifts fromCOSMOS data of the field. Two large superclusters were discovered.The first centred at Z~0.05 but extending for at least 150 h⁻¹Mpc,and the second a projected filament of connecting clusters at Z ~0.11and 23 h⁻¹Mpc long. A selection of 2-D and 3-D statistical analysistechniques have been used to describe the observed large-scale galaxydistribution in this field.A by-product of this work has been the discovery of a new andpowerful means of star/galaxy separation based on magnitudecomparisons between paired objects from both the direct andobjective-prism plates. This technique has revealed ~20% stellarcontamination in the star/galaxy separation based on direct plate data alone. In conclusion, objective-prism galaxy redshifts are valuableinformation for complementing 2-D data in the study of the large-scaledistribution of galaxies from COSMOS measures of Large numbers of UKSTplates. To this end an automatic technique of objective-prismredshift determination should be developed.

[发布机构] University:University of St Andrews;Department:Physics & Astronomy (School of)