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Using VLT/FLAMES optical IFU observations, we present a detailed study of UM448, a nearby Blue Compact Galaxy (BCG) previously reported to have ananomalously high N/O abundance ratio. NTT/SuSI2 images reveal a morphologysuggestive of a merger of two systems of contrasting colour, whilst our H-alphaemission maps resolve UM 448 into three separate regions that do not coincidewith the stellar continuum peaks. UM 448 exhibits complex emission lineprofiles, with lines consisting of a narrow, central component, an underlyingbroad component and a third, narrow blue-shifted component. Radial velocitymaps show signs of solid body rotation across UM 448, with a projected rotationaxis that correlates with the continuum morphology of the galaxy. Aspatially-resolved, chemodynamical analysis is presented. Whilst the easterntail of UM 448 has electron temperatures (Te) that are typical of BCGs, we finda region within the main body of the galaxy where the narrow and broad [O III]4363 line components trace temperatures differing by 5000K and oxygenabundances differing by 0.4 dex. We measure spatially resolved and integratedionic and elemental abundances for O, N, S and Ne throughout UM 448, and findthey do not agree, possibly due the flux-weighting of Te from the integratedspectrum. This has significant implications for abundances derived fromlong-slit and integrated spectra of star-forming galaxies in the nearby anddistant universe. A region of enhanced N/O ratio is indeed found, extended overa ~0.6 kpc^2 region within the main body of the galaxy. Contrary to previousstudies, however, we do not find evidence for a large Wolf-Rayet population,and conclude that WR stars alone cannot be responsible for producing theobserved N/O excess. Instead, the location and disturbed morphology of theN-enriched region suggests that interaction-induced inflow of metal-poor gasmay be responsible.

The merging dwarf galaxy UM 448: chemodynamics of the ionized gas from VLT integral field spectroscopy