A kinematic and abundance survey at the Galactic poles. III

Abstract

A knowledge of the velocity dispersion σ<SUB>w</SUB>(z) of stars for the z (distance above the galactic plane) component of space velocity (W) as a function of both z and composition is necessary to the understanding of the early history of the galactic halo and disk. In this paper the authors specifically address six aspects of galactic structure in the z direction, all of which are related but manifest themselves differently from the observational standpoint: (1) The chemical gradient in the z direction. (2) The composition and kinematics of the individual components of the galactic model. (3) The "continuity" or "decoupling" betweeen the thick disk and halo (at [Fe/H] ≡ -1.00). (4) The σ<SUB>w</SUB>(z) gradient. (5) The presence or lack of solar-composition stars in the halo falling within the zone, and the timescale of the initial halo collapse. (6) The possible "imbalance" of the halo, as proposed by Croswell et al. (1987).