Mapping the starburst in Blue Compact Dwarf Galaxies. PMAS Integral
  Field Spectroscopy of Mrk 1418
  (Abridged) Aims: By means of optical Integral Field Spectroscopy (IFS)
observations, we aim to disentangle and characterize the starburst component in
the BCD Mrk 1418. In particular we propose to study the stellar and ionized gas
morphology, to investigate the ionization mechanism(s) acting in the
interstellar medium, to derive the physical parameters and abundances of the
ionized gas.
  Methods: IFS observations of Mrk 1418 were carried out with PMAS at the 3.5 m
telescope at CAHA. The central 16"x16" were mapped. From these data we built
maps of the most prominent emission lines, namely [OII], H-beta, [OIII],
H-alpha, [NII] and [SII] as well as of several continuum bands, plus maps of
the main line ratios: [OIII]/H-beta, [NII]/H-alpha, [SII]/H-alpha, and
H-alpha/H-beta, and derived the physical parameters and gaseous metal
abundances of the different star-forming regions detected in the field of view.
  Results: Mrk 1418 shows a distorted morphology both in the continuum and in
the ionized gas maps; the current star-formation episode is taking place in
five knots, distributed around the nucleus of the galaxy. The interstellar
medium surrounding these knots is photo-ionized by stars, with no clear
evidence for other excitation mechanisms. The galaxy displays an inhomogeneous
dust distribution, with the high H-alpha/H-beta ratio in the central areas
indicating a large amount of dust. The oxygen abundances derived for the
individual star-forming knots are very similar, suggesting that the ionized
interstellar medium is chemically homogeneous in O/H over spatial scales of
hundreds of parsecs. This abundance (Z~0.4 Z_solar from the empirical
calibrations) places Mrk 1418 among the high metallicity BCD group.
