The Environment of Passive Spiral Galaxies in the SDSS

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. 1a ndMr ∗ < −20.5; 25813 galaxies) of the Sloan Digital Sky Survey data, we found 73 (0.28±0.03%) passivespiral galaxiesand studied their environments. It is found that passivespiral galaxies exist in a local galaxy density of 1–2Mpc −2 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.