B and V CCD photometry of southern, extreme late-type spiral galaxies

We present B and V CCD aperture photometry for a morphologically-selected sample of 49 southern, extreme late-type spiral galaxies. All objects are moderate-to-low surface brightness Local Supercluster field galaxies that were detected previously in HI surveys. Our sample features objects that have optical luminosities, optical sizes, and H I masses which are at the low end for spiral galaxies. These objects are not a new class of galaxy, but are examples of a common type of spiral galaxy that has been under-represented in nearby galaxy samples. We discuss the Limitations of standard photometric techniques as applied to extreme late-type spirals, and adopt a simple method of characterizing the light distributions of such objects in terms of aperture magnitudes, colors, color gradients, ''mean disk scales,'' and optical structure. In many respects, the global properties of extreme late-type spirals are intermediate between irregulars and ordinary high surface brightness spiral galaxies. While our sample galaxies generally have regular structures and well-defined centers, some of the objects are very blue and/or have large gas fractions (M-HI/L-V similar to 3-9), i.e., properties which have been traditionally associated with dwarf irregular galaxies. Several galaxies become redder with increasing radius, a trend which seems to be uniquely found in certain dwarf and very late-type disk galaxies. In addition, we find bars to be common in extreme late-type spirals. Our sample exhibits a diverse array of structural properties and morphologies in galaxies with otherwise similar physical parameters (e.g., M-B, M-HI, B-V) A number of the galaxies possess unresolved, point-like nuclei which may be related to low-luminosity AGNs or to M33-like compact nuclei. Finally, several of the galaxies show distinctive surface brightness ''steps'' in their disks, demonstrating that even small, late-type spirals can have multi-component disks. (C) 1997 American Astronomical Society.