  We investigate the warm ionized gas in the blue compact galaxy (BCG) Haro 14
by means of integral field spectroscopic observations taken with the MUSE/VLT.
The large FoV of MUSE and its unprecedented sensitivity enable observations of
the galaxy nebular emission up to large galactocentric distances. This allowed
us to trace the ionized gas morphology and ionization structure up to
kiloparsec scales and, for the first time, to accurately investigate the
excitation mechanism operating in the outskirts of a typical BCG. The intensity
and diagnostic maps reveal at least two highly distinct components of ionized
gas: the bright central regions, mostly made of individual clumps, and a faint
component which extends up to kiloparsec scales and consists of widespread
diffuse emission, well-delineated filamentary structures, and faint knots.
Noteworthy are the two curvilinear filaments extending up to 2 and 2.3 kpc
southwest, which likely trace the edges of supergiant expanding bubbles driven
by galactic outflows. We find that while the central clumps in Haro 14 are
HII-region complexes, the morphology and line ratios of the whole
low-surface-brightness component are not compatible with star formation
photoionization. In the spatially resolved emission-line-ratio diagnostic
diagrams, spaxels above the maximum starburst line form the majority. Moreover,
our findings suggest that more than one alternative mechanism is ionizing the
outer galaxy regions. The properties of the diffuse component are consistent
with ionization by diluted radiation and the large filaments and shells are
most probably shocked areas at the edge of bubbles. The mechanism responsible
for the ionization of the faint individual clumps observed in the galaxy
periphery is more difficult to assess. These clumps could be the shocked debris
of fragmented shells or regions where star formation is proceeding under
extreme conditions.
