The Ages and Metallicities of Dwarf Ellipticals

James Schombert
Univ. of Oregon

A galaxy is a collect of stars, gas and dust bound together by their common gravitational pull. Galaxies range from 10,000 to 200,000 light-years in size Galaxies have certain features in common. Gravity holds their stars together. The densest region is in the center, called a core or bulge. Some galaxies are disk shaped with pinwheel arms, called spirals. Others are smooth and elliptical in shape.

Galaxies are composed of the following in varying portions:

Stellar objects
  1. normal stars
  2. brown dwarfs
  3. white dwarfs
  4. black dwarfs (after a long time)
  5. neutron stars
  6. black holes
ISM
  1. neutral hydrogen
  2. molecular clouds
  3. HII regions
  4. SN plasma
Dark Matter

Most of the mass of a galaxy is in dark matter and stellar reminants, but almost all of the optical luminosity is due to photons emitted from normal stars. Thus, a study of the appearence and total luminosity of galaxies with time is a question of the behavior of the stellar population of which they are composed.