Roger G. Clowes

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A large quasar group (LQG) of particularly large size and high membership has been identified in the DR7QSO catalogue of the Sloan Digital Sky Survey. It has characteristic size (volume1/3) ∼500 Mpc (proper size, present epoch), longest dimension ∼1240 Mpc, membership of 73 quasars and mean redshift z̄ = 1.27. In terms of both size and membership, it is the(More)
This paper describes an algorithm based on the 2D approach of Allard & Fraley that uses Voronoi tessellation and a non-parametric maximum likelihood estimator. We have designed a 3D version of this algorithm which detects multiple clusters of points immersed in background noise; its application to the detection of galaxy clusters in redshift space, using(More)
Based on observations with the Blanco 4m telescope at CTIO, which is operated by the Association of Universities for Research in Astronomy, Inc. under contract to the National Science Foundation. Laboratory for Astronomy and Solar Physics, NASA Goddard Space Flight Center, Code 681, Greenbelt MD 20771, USA National Optical Astronomy Observatory, P.O. Box(More)
We present the catalogue of the Mg II absorption systems detected at a high significance level using an automated search algorithm in the spectra of quasars from the 12th data release of the Sloan Digital Sky Survey. A total of 266,433 background quasars were searched for the presence of absorption systems in their spectra. The continuum modelling for the(More)
We have investigated the strength of ultraviolet Fe II emission from quasars within the environments of Large Quasar Groups (LQGs) in comparison with quasars elsewhere, for 1.1 6 z̄LQG 6 1.7, using the DR7QSO catalogue of the Sloan Digital Sky Survey. We use the Weymann et al. W2400 equivalent width, defined between the rest-frame continuum-windows(More)
The Chile-UK quasar survey, a new-generation 140 deg UVX survey to B = 20, is now ∼ 25% complete. The catalogue currently contains 319 quasars and 93 emission line galaxies. Using the minimal-spanning tree method, we have independently confirmed the ∼ 200 h Mpc group of quasars at z ≃ 1.3 discovered by Clowes & Campusano (1991). We have discovered a new ∼(More)
  • GALAXIES AT, BREAK GALAXIES, +11 authors I. K. Söchting
  • 2017
The nature of galaxy structures on large scales is a key observational prediction for current models of galaxy formation. The Sloan Digital Sky Survey (SDSS) and the 2dF galaxy survey have revealed a number of structures on 40–150 h−1 Mpc scales at low redshifts, and some even larger ones. To constrain galaxy number densities, luminosities, and stellar(More)
We are looking at quasar environment in the context of large-scale structure (LSS) — a new approach, giving a more informed interpretation of quasar-galaxy correlations. This paper presents our first results for a sample of z ∼ 0.3 quasars. We are using Voronoi tessellation applied in colour (BJ−R) slices for the detection of galaxy clusters and the minimal(More)
We investigate the strength of ultraviolet Fe II emission in fainter quasars compared with brighter quasars for 1.0 6 z 6 1.8, using the SDSS (Sloan Digital Sky Survey) DR7QSO catalogue and spectra of Schneider et al., and the SFQS (SDSS Faint Quasar Survey) catalogue and spectra of Jiang et al. We quantify the strength of the UV Fe II emission using the(More)