Spatially resolved spectroscopy and chemical history of star-forming
  galaxies in the Hercules cluster: the effects of the environment
  Spatially resolved spectroscopy has been obtained for a sample of 27
star-forming (SF) galaxies selected from our deep Halpha survey of the Hercules
cluster. We have applied spectral synthesis models to all emission-line spectra
of this sample using the population synthesis code STARLIGHT. We have obtained
fundamental parameters of the stellar components, as the mean metallicity and
age, and we have corrected the emission-line spectra for underlying stellar
absorption. O/H and N/O gas chemical abundances were obtained using the latest
empirical calibrations. The effects of cluster environment on the chemical
evolution of galaxies and on their mass-metallicity (MZ) and
luminosity-metallicity (LZ) relations were studied combining the derived gas
metallicities, the mean stellar metallicities and ages, the masses and
luminosities of galaxies and their existing HI data. We have found that our
Hercules SF galaxies divide into three main subgroups: a) chemically evolved
spirals with truncated ionized-gas disks and nearly flat oxygen gradients,
witnessing the effect of ram-pressure stripping, b) chemically evolved
dwarfs/irregulars populating the highest local densities, possible products of
tidal interactions in preprocessing events, or c) less metallic dwarf galaxies
which appear to be "newcomers" to the cluster, experiencing pressure-triggered
star-formation. Most Hercules SF galaxies follow well defined MZ and LZ
sequences (for both O/H and N/O); though the dwarf/irregular galaxies located
at the densest regions appear to be outliers to these global relations,
suggesting a physical reason for the dispersion in these fundamental relations.
The Hercules cluster appears to be currently assembling via the merger of
smaller substructures, providing an ideal laboratory where the local
environment has been found to be a key parameter to understand the chemical
history of galaxies.
