  Using VLT/FLAMES optical IFU observations, we present a detailed study of UM
448, a nearby Blue Compact Galaxy (BCG) previously reported to have an
anomalously high N/O abundance ratio. NTT/SuSI2 images reveal a morphology
suggestive of a merger of two systems of contrasting colour, whilst our H-alpha
emission maps resolve UM 448 into three separate regions that do not coincide
with the stellar continuum peaks. UM 448 exhibits complex emission line
profiles, with lines consisting of a narrow, central component, an underlying
broad component and a third, narrow blue-shifted component. Radial velocity
maps show signs of solid body rotation across UM 448, with a projected rotation
axis that correlates with the continuum morphology of the galaxy. A
spatially-resolved, chemodynamical analysis is presented. Whilst the eastern
tail of UM 448 has electron temperatures (Te) that are typical of BCGs, we find
a region within the main body of the galaxy where the narrow and broad [O III]
4363 line components trace temperatures differing by 5000K and oxygen
abundances differing by 0.4 dex. We measure spatially resolved and integrated
ionic and elemental abundances for O, N, S and Ne throughout UM 448, and find
they do not agree, possibly due the flux-weighting of Te from the integrated
spectrum. This has significant implications for abundances derived from
long-slit and integrated spectra of star-forming galaxies in the nearby and
distant universe. A region of enhanced N/O ratio is indeed found, extended over
a ~0.6 kpc^2 region within the main body of the galaxy. Contrary to previous
studies, however, we do not find evidence for a large Wolf-Rayet population,
and conclude that WR stars alone cannot be responsible for producing the
observed N/O excess. Instead, the location and disturbed morphology of the
N-enriched region suggests that interaction-induced inflow of metal-poor gas
may be responsible.
