Passive spiral galaxies: a stepping stone to S0s?

We investigate the stellar population properties of nine passive spiral galaxies in the CALIFA survey. They have NUV-r > 5 and no/weak nebular emission lines in their spectra. They lie in the redshift range of 0.001 < z < 0.021 and have stellar mass range of 10.2 < ${\log}(M{\star}/M{\odot})$ < 10.8. We analyze the stellar populations out to two effective radius, using the best-fitting model to the measured absorption line-strength indices in the Lick/IDS system. We compare the passive spirals with S0s selected in the same mass range. S0s cover a wide range in age, metallicity, and [${\alpha}/Fe$], and stellar populations of the passive spirals are encompassed in the spread of the S0 properties. However, the distribution of passive spirals are skewed toward higher values of metallicity, lower [${\alpha}/Fe$], and younger ages at all radii. These results show that passive spirals are possibly related to S0s in their stellar populations. We infer that the diversity in the stellar populations of S0s may result from different evolutionary pathways of S0 formation, and passive spirals may be one of the possible channels.