Bar-induced central star formation as revealed by integral field
  spectroscopy from CALIFA
  We investigate the recent star formation history (SFH) in the inner region of
57 nearly face-on spiral galaxies selected from the Calar Alto Legacy Integral
Field Area (CALIFA) survey. For each galaxy we use the integral field
spectroscopy from CALIFA to obtain two-dimensional maps and radial profiles of
three parameters that are sensitive indicators of the recent SFH: the 4000\AA\
break (D$_n$(4000)), and the equivalent width of H$\delta$ absorption
(EW(H$\delta_A$)) and H$\alpha$ emission (EW(H$\alpha$)). We have also
performed photometric decomposition of bulge/bar/disk components based on SDSS
optical image. We identify a class of 17 "turnover" galaxies whose central
region present significant drop in D$_n$(4000), and most of them
correspondingly show a central upturn in EW(H$\delta_A$) and EW(H$\alpha$).
This indicates that the central region of the turnover galaxies has experienced
star formation in the past 1-2 Gyr, which makes the bulge younger and more
star-forming than surrounding regions. We find almost all (15/17) the turnover
galaxies are barred, while only half of the barred galaxies in our sample
(15/32) are classified as a turnover galaxy. This finding provides strong
evidence in support of the theoretical expectation that the bar may drive gas
from the disc inward to trigger star formation in galaxy center, an important
channel for the growth/rejuvenation of pseudobulges in disc galaxies.
