Interaction effects on galaxy pairs with GeminiGMOS-III: Stellar
  population synthesis
  We present an observational study of the impacts of the interactions on the
stellar population in a sample of galaxy pairs. Long-slit spectra in the
wavelength range 3440-7300 {\AA} obtained with the Gemini Multi-Object
Spectrograph (GMOS) at Gemini South for fifteen galaxies in nine close pairs
were used. The spatial distributions of the stellar population contributions
were obtained using the stellar population synthesis code STARLIGHT. Taking
into account the different contributions to the emitted light, we found that
most of the galaxies in our sample are dominated by the young/intermediate
stellar populations. This result differs from the one derived for isolated
galaxies where the old stellar population dominates the disc surface
brightness. We interpreted such different behavior as being due to the effect
of gas inflows along the disk of interacting galaxies on the star formation in
a time scale of the order of about 2Gyr. We also found that, in general, the
secondary galaxy of the pairs has a higher contribution of the young stellar
population than the primary one. We compared the estimated values of the
stellar and nebular extinctions derived from the synthesis method and the
H{\alpha}/H\b{eta} emission-line ratio finding that the nebular extinctions are
systematically higher than stellar ones by about a factor of 2. We did not find
any correlation between nebular and stellar metallicities. We neither found a
correlation between stellar metallicities and ages while a positive correlation
between nebular metallicities and stellar ages was obtained, with the older
regions being the most metal-rich.
