1 Introduction

A good knowledge of the local galaxian neighbourhood is prerequisite for an understanding of the distant (early) universe. Deep images, such as the spectacular Hubble Deep Field, can only be interpreted properly if the dwarf galaxy content of the local universe is very well known. However, studies of nearby dwarf galaxies have until recently concentrated on the Local Group (LG), a rather small volume of space. A larger piece of the local universe is captured in the "10 Mpc Catalogue'' of galaxies by Kraan-Korteweg & Tammann (1979), updated by Schmidt & Boller (1992a). This list is intended to contain all galaxies with radial velocities of less than 500 kms^-1 as referred to the centroid of the LG, i.e. lying within a distance of about 10 Mpc. At present, the list includes c.a. 300 (mostly dwarf) galaxies, but this number is bound to grow due to continued efforts to detect extremely faint and diffuse nearby stellar systems (Karachentseva & Karachentsev 1998).

Unfortunately, the available photometric data on "10 Mpc objects'' is relatively scarce and not very reliable for the fainter galaxies (Patterson & Thuan 1996). We have therefore started a long-term programme to do systematic multicolour imaging of possibly all dwarfish objects in the 10 Mpc volume. The goal is not only to get total magnitudes in order to assess the true shape of the faint end of the local luminosity function of galaxies, but also to derive all relevant structural parameters for these dwarfs and to compare them with existing data on the dwarf galaxy populations of, foremost, the Virgo and Fornax clusters e.g. Binggeli & Cameron (1991), in order to get clues on galaxy evolution in different environnments.

Most galaxies within 10 Mpc distance are organized into a small number of well-known groups of galaxies; essentially these are the IC 342, M81, M101, CVnI, Cen A, and Scl groups (Schmidt & Boller 1992b). Following previous work on the M81 group dwarfs (Bremnes et al. 1998; Lesaffre et al. 1999), herefater Papers I & II, we here present CCD photometric data in the B and R photometric bands for the 11 known M101 group dwarf members, as well as 10 field dwarfs in the vicinity of M101. A short description of the M101 group is given in the following section. The photometric data presented here (Sect. 4) will be combined with those of previous data papers. An interpretation and scientific discussion of this material is planned to follow in a future paper of this series.