The Structure of the Irregular Galaxy NGC 4449

NGC 4449 is a typical Type I irregular galaxy, used by Hubble as a type example of its class. We have used photographs in V, B, and Ha, with photoelectric surface photometry, for the purpose of study- ing its structure and content. The distance to NGC 4449, determined from the diameters of the largest of the H II regions detected, is 3 3 ± 0 2 Mpc. Its mean dimension is 4 5 kpc, and its absolute magnitude is M~ = -18 0. Isophotes in two colors show the dominance of a large number of resolved features. Of these, at least eighty-one are H ii regions, and the remainder are globular clusters, associations, and bright stars (M~ -7). Resolved features are virtually absent from one quadrant. In an attempt to determine the underlying structure of the galaxy, we have plotted a set of isophotes from tracings from which the resolved features that stand alone have been removed. The result shows that the older star population is arranged roughly rectangularly, with one corner anomalously rounded