The Local Group Dwarf Irregular Galaxy NGC 6822.I.The Stellar Content

We present deep UBVRI CCD photometry of the resolved stellar content of the Local Group Dwarf Irregular Galaxy NGC 6822. The main advantage of this new data is that the color-magnitude (CM) diagrams obtained contain stars of virtually all ages and metallicities and hence are a record of the full star formation history of the galaxy. The wide field covered permits unbiased analysis of the whole galaxy. In turn, the large number of NGC 6822's measured stars (~18000) ensures that even short-lived stellar evolutionary phases like AGB will be populated by a significant number of stars. A derivation from these data of the full star formation history of the galaxy, using synthetic CM diagrams, will be presented in two forthcoming papers. In the present paper, we discuss all the preliminary steps to perform that analysis: we discuss the data, and we present a detailed study of crowding effects on the photometry using artificial stars tests. We show the process to obtain all the necessary information for the simulation of observational effects on the synthetic CM diagrams to produce model CM diagrams directly comparable with the observed CM diagrams. In addition, a new estimate of distance and reddening using Cepheids is presented and compared with the result for the distance calculated using the tip of the red giant branch as a distance indicator. A distance modulus of (m-M)_0_ = 23.49+/-0.08 and a reddening of E(B-V) = 0.24+/-0.03 have been obtained.