Stellar populations of nine passive spiral galaxies from the CALIFA
  survey: are they progenitors of S0s?
  We investigate the stellar population properties of passive spiral galaxies
in the CALIFA survey. Nine spiral galaxies that have NUV-r > 5 and no/weak
nebular emission lines in their spectra are selected as passive spirals. Our
passive spirals 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. They clearly lie in the
domain of early-type galaxies in the WISE IR color-color diagram. 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 find that stellar populations of the passive spirals span a wide range, even
in their centers, and hardly show any common trend amongst themselves either.
We compare the passive spirals with S0s selected in the same mass range. S0s
cover a wide range in age, metallicity, and [a/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 [a/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.
