Abstract
In previous work on galaxy clusters, several authors reported the discovery of an unusual population of galaxies, which have spiral morphologies, but do not show any star-formation activity. These galaxies are called "passive spirals", and have been interesting since it has been difficult to understand the existence of such galaxies. Using a volume-limited sample (0.05 < z < 0.1 and M <sub>r</sub> *- < -20.5; 25813 galaxies) of the Sloan Digital Sky Survey data, we found 73 (0.28±0.03%) passive spiral galaxies and studied their environments. It is found that passive spiral galaxies exist in a local galaxy density of 1-2Mpc <sup>-2</sup> and have a 1-10 cluster-centric virial radius. Thus, the origins of passive spiral galaxies are likely to be cluster-related. These characteristic environments coincide with a previously reported environment where the galaxy star-formation rate suddenly declines and the so-called morphology-density relation turns. It is likely that the same physical mechanism is responsible for all of these observational results. The existence of passive spiral galaxies suggests that a physical mechanism that works calmly is preferred to dynamical origins such as major merger/interaction since such a mechanism would destroy the spiral-arm structures. Compared with the observed cluster galaxy evolution such as the Butcher-Oemler effect and the morphological Butcher-Oemler effect, passive spiral galaxies are likely to be a key galaxy population in transition between red, elliptical/S0 galaxies in low-redshift clusters and blue, spiral galaxies more numerous in higher-redshift clusters.