Luminosity--Line Width Relations and the Extragalactic Distance Scale. I. Absolute Calibration

Multicolor CCD photometry is presented for a sample of 15 spiral and irregular members of the Local, Sculptor, and M81 groups with M_B_ < = 16.0 and relevant as potential calibrators of the luminosity- line width relations. The sample contains those galaxies for which a ground-based study of Cepheid variables could provide accurate distances and hence an absolute calibration for the relations. Unfortunately, only six of the systems presently have reliable independent distance estimates, but this number is sufficient to provide a reasonable calibration. Distance-independent relations involving line width, color, and mean surface brightness are also discussed. These relations are used to examine the possibility of systematic differences between local galaxies used to calibrate the relations and more distant samples. It is shown that while the "local calibrators" are indistinguishable from a large sample of field galaxies they are bluer in the mean than a large sample of cluster galaxies. In the B band a systematic correction of ~12% in distance is required for cluster samples, but it is argued that the effect in near-infrared passbands is negligible. No other evidence for systematic differences between the photometric/kinematic scaling properties of galaxies is discernible over the range of environments sampled by this investigation. These data imply that the primary source of uncertainty in the extragalactic distance scale now lies with the Galactic calibration of the Cepheid and RR Lyrae variables. The new zero- point calibrations are consistent with previous calibrations of the luminosity-line width relations which lead to high values of H_0_.