| Abstract | The bright galaxy NGC 7603 has an extended spiral arm which appears to end exactly on a small, high surface brightness companion (referred to here as NGC 7603B). However, the companion has a much larger redshift than that of NGC 7603, placing it conventionally almost twice as far away. Deep plates presented here show that NGC 7603 actually extends for some considerable distance beyond the companion, and that there is evidence for past interactions which can explain the disturbed structure. Narrow-band H-alpha images show no sign of strong disturbances in the feature apparently leading to NGC 7603B, which would be expected if tidal interaction is currently taking place. A velocity dispersion and a magnitude are also provided for the companion, enabling consideration of the Faber-Jackson relation. Regrettably, the two possible locations for NGC 7603B in the luminosity-dispersion diagram, corresponding to the redshift distances for it and for NGC 7603, bracket the current uncertainties in this relation, and no firm conclusion can be reached. However, two tentative tertiary distance estimates for NGC 7603B agree better with its own redshift. Other redshift measurements in the vicinity reveal the presence of a group at the same distance as NGC 7603, but there does not appear to be a cluster at the companion's distance (although there is a yet more distant group). No strong anomalies have been found which would force the acceptance of the existence of a noncosmological redshift. |
