Galaxy bulge

The metallicity distribution of globular clusters in the Galaxy has a metal-rich peak at [Fe/H] -0.5 and a metal-poor peak at [Fe/H] -1.6 (e.g. Cote 1999), where most of the metal-rich ones are bulge clusters. Metallicities for samples of field stars were derived by McWilliam Rich (1994, hereafter MR94), Sadler et al. (1996), Ramirez et al. (2000). Zoccali et al. (2003) presented the... 

The Galactic Bulge contains about 20 percent of the Galaxy s stellar mass. Theories of its formation include a primordial free-fall collapse, remnants of accretion episodes, or secular evolution of bar instabilities ([1]). Accurate stellar abundance determinations can help distinguish between these models. 

Figure 3.38 shows a schematic cross-sectional view of the Galaxy, indicating the main stellar population groups (disk, bulge, halo and solar cylinder) that will figure in subsequent discussions and Table 7.9 gives some relevant statistics. 

Parameters of dynamically hot galaxies , i.e. various classes of ellipticals and the bulges of spirals, generally lie close to a Fundamental Plane in the 3-dimensional space of central velocity dispersion, effective surface brightness and effective radius or equivalent parameter combinations (Fig. 11.10). This is explained by a combination of three factors the Virial Theorem, some approximation to... 

First, it is useful to know that a model spiral galaxy can be considered to consist of a central spherical bulge component, embedded in a rotating disk of stellar and gaseous material with the whole embedded in a spherical halo of very diffuse gas and halo stars. It is conventionally believed that this latter component is much more massive than it appears, with the deficit made up of dark matter. ... 

The probable black hole in the Andromeda Galaxy s central bulge has 30 million times the mass of the Sun. 

Fig. 3. Distribution of stars and interstellar matter in the Galaxy. The lower part of the diagram is a cross section perpendicular to the galactic plane. Globular clusters are the oldest stellar systems and must therefore have been formed in the early evolutionary stages of the Galaxy. The mass of the stars, however, forms a flat layer with a nuclear bulge in the center. The interstellar matter forms an even flatter layer which widens up towards the edges of the Galaxy.

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