97 10 25 8 v 1 2 3 O ct 1 99 7 Metal systems of the Lyman forest
An extremely careful analysis of the forest of weak metal-line systems at z ∼ 2 has allowed the separation into individual 'single-phase ionization' components with accurate parameters. The systems typically span several hundred km s −1 and within each the components show a strong coherence in their ioniza-tion properties. A general feature of the observed systems is the presence of high ionization broad components which co-exist in velocity space with more numerous, narrow, lower ionization components. From a sample of components extending to z ∼ 3.5, taken either individually or as system totals, no rapid evolution is found in the column density ratio N(Si IV)/N(C IV), contrary to previous indication of a large change near z = 3.1. Comparisons of component ion ratios including Si IV, C IV, C II and Si II from the sample at z ∼ 2 with CLOUDY derived values using several model ionizing spectra show the general dominance of the metagalactic ionizing background over local stellar radiation and give Si/C distributed 1–3 times the solar value. Indications of the evolution of structure are highlighted.
Cold Gas at High Redshift Netherlands Foundation for Research in Astronomy
We discuss the current observational and theoretical issues concerning cold gas at high redshift and present simulations showing how a number of observational issues can be resolved with planned future instrumentation.
The history and development of the dental surveyor--Part III.
The dental surveyor is an indispensable instrument capable of performing a number of prosthodontic procedures. Surprisingly, the technique of surveying casts as part of the treatment planning procedure did not emerge until early in the twentieth century. This article reviews the origins and early use of the dental surveyor. It includes features common to all surveyors as well as the principal uses of these instruments.