Galaxies dwarf elliptical

Fig. 11.2. Mean stellar iron abundances as a function of luminosity in dwarf spheroidals (filled circles), dwarf ellipticals (open circles), dSph/dlrr transition galaxies (filled diamonds) and dwarf irregulars (open diamonds). Baryonic luminosity in the right panel includes the additional luminosity that irregulars would have if their gas were converted into stars. After Grebel, Gallagher and Harbeck (2003).

But the history of the Milky Way may not be so simple. Detailed studies of the globular clusters in the halo and the different ages of stars in the halo and disk reveal some anomalies. For example, the contents of the halo do not always orbit in the same direction that the disk does. In addition, portions of the halo have very different ages. From this evidence, astronomers have concluded that the Milky Way may have formed as the result of a merger of smaller systems such as globular clusters or dwarf elliptical galaxies. 

In these lectures I present a highly opinionated review of the observed patterns of metallicity and element abundance ratios in nearby spiral, irregular, and dwarf elliptical galaxies, with connection to a number of astrophysical issues associated with chemical evolution. I also discuss some of the observational and theoretical issues associated with measuring abundances in H II regions and gas and stellar surface densities in disk galaxies. Finally, I will outline a few open questions that deserve attention in future investigations. 

Abundances in Local Group Dwarf Elliptical Galaxies... 

Fig. 11.16. Median metal abundance per unit true yield as a function of final mass with observations of dwarf spheroidal and elliptical galaxies superposed.

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