The distribution of dark matter in the dwarf galaxy DDO 170

This paper reports the results of observations on the dwarf galaxy DDO 170 (absolute magnitude -15.15) and examines the implications of these observations on the distribution of dark matter. Using H I images and new photometry, three component models of the DDO-170 mass distribution are developed: (1) a luminous disk with a constant mass/luminosity ratio, (2) a gas disk whose mass is determined by H I flux, and (3) a dark halo. It is found that the mass-to-luminosity ratio derived from the last point of the rotation curve (12.5 kpc) 56, the ratio of gas mass (derived from the 21 cm flux) to blue luminosity is about 3.7 in solar units, and that the DDO 170 is the smallest galaxy where the basic halo parameters (core radius and asymptotic velocity) are determined by fitting detailed mass models. It was also found that the DDO 170 has a companion with a projected separation of 62 kpc and a line-of-sight velocity difference of 85 km/sec. (I.S.)