Star formation suppression and bar ages in nearby barred galaxies
  We present new spectroscopic data for 21 barred spiral galaxies, which we use
to explore the effect of bars on disk star formation, and to place constraints
on the characteristic lifetimes of bar episodes. The analysis centres on
regions of heavily suppressed star formation activity, which we term 'star
formation deserts'. Long-slit optical spectroscopy is used to determine H beta
absorption strengths in these desert regions, and comparisons with theoretical
stellar population models are used to determine the time since the last
significant star formation activity, and hence the ages of the bars. We find
typical ages of approx. 1 Gyr, but with a broad range, much larger than would
be expected from measurement errors alone, extending from about 0.25 Gyr to
more than 4 Gyr. Low-level residual star formation, or mixing of stars from
outside the 'desert' regions, could result in a doubling of these age
estimates. The relatively young ages of the underlying populations coupled with
the strong limits on the current star formation rule out a gradual exponential
decline in activity, and hence support our assumption of an abrupt truncation
event.
