The Outer Regions of the Galactic Bulge : II { AnalysisRodrigo

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 (Ibata & Gilmore 1995), 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 kine-matic 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 ts. The bulge has a well-determined linear rotation curve over the range 700pc R 3500pc with amplitude 25 km s 1 kpc 1. Several velocity dispersion models are found to t the data. We test the oblate isotropic bulge model of Kent (1992) by integrating the kinematics predicted by that model into our Galaxy model, and comparing with our data. We nd reasonable agreement except in the most distant of our elds from the Galactic centre. We do not nd a signiicant 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 (1982) 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 elds where the photometric calibration is adequate. Our metal-licity index measures the Mgb feature, and is calibrated against local eld 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 metallicities in these elds is Fe=H] 0:3 and does not vary signiicantly over the regions investigated. This mean is very close to the mean abundance of K giants observed recently in Baade's Window (McWilliam & Rich 1994). That is, there is no detectable abundance gradient in the Galactic bulge over the galactocentric range 500pc R GC 3500pc. 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 disk, together with a closed-box`simple model' of chemical evolution with yield 0:7Z to describe the bulge component. We derive the distribution function of speciic angular momentum for …