THE OUTER REGIONS OF THE GALACTIC BULGE .2. ANALYSIS

Velocity, chemical abundance and spatial distribution data for some 1500 K and M giants in the Galactic bulge, which are presented in an accompanying paper, are analysed. We provide three levels of analysis: an almost model-independent determination of basic symmetry properties of the Galactic bulge; a more detailed analysis based on conservative assumptions, which investigates the basic kinematic and chemical abundance distributions in terms of a few parameters; and a more detailed investigation of possible functional forms for the density and kinematic distributions that are consistent with the data using maximum-likelihood fits. The bulge has a well-determined linear rotation curve over the range 700 pc less than or equal to R less than or equal to 3500 pc, with amplitude similar to 25 km s(-1) kpc(-1). Several velocity dispersion models are found to fit the data. We test the oblate isotropic bulge model of Kent by integrating the kinematics predicted by that model into our Galaxy model, and comparing with our data. We find reasonable agreement except in the most distant of our fields from the Galactic Centre. We do not find a significant requirement for asymmetry or a bar from our kinematics. Our data allow a quantitative comparison between the Milky Way bulge and the spiral galaxy bulges studied by Kormendy & Illingworth over a similar Galactocentric distance range; the Galactic bulge appears to be characteristic of the extragalactic bulge population. We determine the metallicity distribution of K giants in that subset of our fields where the photometric calibration is adequate. Our metallicity index measures the Mg'b' features, and is calibrated against local field standards. Thus our abundance scale assumes a similar relationship between [Mg/Fe] and [Fe/H] in the bulge to that which is seen in the solar neighbourhood. Given that assumption, the mean metallicity in these fields is [Fe/H] approximate to -0.3 and does not vary significantly over the regions investigated. This mean is very close to the mean abundance of K giants observed recently in Baade's Window. That is, there is no detectable abundance gradient in the Galactic bulge over the Galactocentric range 500 pc less than or equal to R(GC) less than or equal to 3500 pc. The overall bulge abundance distribution is in good agreement with a model that combines standard solar neighbourhood determinations of the abundance distribution functions for the halo and thick disc, together with a closed-box 'simple model' of chemical evolution with yield similar to 0.7 Z. to describe the bulge component. We derive the distribution function of specific angular momentum for the bulge from our data, and compare it with determinations for the halo, the thick disc and the thin disc from Wyse & Gilmore. We confirm that the bulge and the halo have angular momentum distributions that are indistinguishable, as do the thick disc and the thin disc. The bulge-halo distribution is, however, very different from the thick disc-thin disc distribution. This is perhaps the strongest available clue to the evolutionary relationships between different Galactic structural components.