New Light in Star-Forming Dwarf Galaxies: The PMAS Integral Field View
  of the Blue Compact Dwarf Galaxy Mrk 409
  We present an integral field spectroscopic study of the central 2x2 kpc^2 of
the blue compact dwarf galaxy Mrk 409, observed with the Potsdam MultiAperture
Spectrophotometer. This study focuses on the morphology, two-dimensional
chemical abundance pattern, excitation properties and kinematics of the ionized
interstellar medium in the starburst component. We also investigate the nature
of the extended ring of ionized gas emission surrounding the bright nuclear
starburst region of Mrk 409. PMAS spectra of selected regions along the ring,
interpreted with evolutionary and population synthesis models, indicate that
their ionized emission is mainly due to a young stellar population with a total
mass of ~1.5x10^6 M_sun, which started forming almost coevally ~10 Myr ago.
This stellar component is likely confined to the collisional interface of a
spherically expanding, starburst-driven super-bubble with denser, swept-up
ambient gas, ~600 pc away from the central starburst nucleus. The spectroscopic
properties of the latter imply a large extinction (C_H-beta>0.9), and the
presence of an additional non-thermal ionization source, most likely a
low-luminosity Active Galactic Nucleus. Mrk 409 shows a relatively large oxygen
abundance (12+log(O/H)~8.4) and no chemical abundance gradients out to R~600
pc. The ionized gas kinematics displays an overall regular rotation on a
northwest-southwest axis, with a maximum velocity of 60 km/s; the total mass
inside the star-forming ring is about 1.4x10^9 M_sun.
