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Using the PMAS Integral Field Unit on the Calar Alto 3.5 m telescope, we observed the southern component (Markarian 59) of the 'cometary' starburst galaxy NGC 4861. Mrk 59 is centred on a giant nebula and concentration of stars 1 kpc in diameter. Strong |$\rm H\,\alpha$| emission points to a star-formation rate (SFR) at least 0.47  |$\rm M_{\odot }\, yr^{-1}$|⁠. Mrk 59 has a very high [O  iii ] |$\rm \lambda 5007/H\,\beta$| ratio, reaching 7.35 in the central nebula, with a second peak at a star-forming hotspot further north. Fast outflows are not detected but nebular motion and galaxy rotation produce relative velocities up to 40 km  |$\rm s^{-1}$|⁠. Spectral analysis of different regions with 'Fitting Analysis using Differential evolution Optimization' (FADO) finds that the stars in the central and 'spur' nebulae are very young, |$\rm \le 125~Myr$| with a large |$\rm \lt 10~Myr$| contribution. Older stars (⁠|$\rm \sim 1~Gyr$|⁠) make up the northern disk component, while the other regions show mixtures of 1 Gyr age with very young stars. This and the high specific SFR |$\rm \sim 3.5~Gyr^{-1}$| imply a bimodal star formation history, with Mrk 59 formed in ongoing starbursts fuelled by a huge gas inflow, turning the galaxy into an asymmetric 'green pea' or blue compact dwarf. We map the He  ii  λ4686 emission, and identify a broad component from the central nebula, consistent with the emission of ∼300 Wolf–Rayet stars. About a third of the He  ii  λ4686 flux is a narrow line emitted from a more extended area covering the central and spur nebulae, and may have a different origin. [ABSTRACT FROM AUTHOR]

We study the radial distribution of oxygen and nitrogen abundances in H ii regions in 350 galaxies observed in the CALIFA survey using the semi-empirical N-sensitive code Hii-Chi-mistry. A separate analysis of N/O when using [N ii] is justified as the dispersion in the O/H-N/O diagram is very large. In fact different O/H and N/O slope distributions and flattening in the outskirts are obtained.On the other hand there is a tight correlation between O/H and N/O when the values of the fittings at the effective radius are considered as representative of each galaxy. [ABSTRACT FROM PUBLISHER]