Mass Determinations and Dark Matter at Intermediate Scales

Abstract

The issue of “dark matter” in astronomy is extremely confusing. Difficulties exist on two levels. First there are the, in principle, straightforward scientific questions of measurement. A certain region of space is studied, and by some technique, the mass within it is determined. Separately the energy output in some wavelength band from the region is measured and then, with due allowance for distance uncertainties, a “mass-to-light” ratio is determined. These measurements are difficult, with the results affected both by small number statistical uncertainties (as when using globular clusters to determine the mass of the galactic halo), measurement errors (as with binary galaxies), and systematic questions of interpretation (as with X-ray emitting gas around galaxies). Ultimately, with patience and skill these problems have been reduced and, as we shall see in subsequent sections of this report, there exists moderate agreement among observers concerning the large mass (∼ 1012 M⊙) and high mass-to-light ratio (M/LB > 100 M⊙/L⊙) for material integrated over distances in the range (30 kpc < r < 300 kpc) from the centers of giant galaxies.