The heart of NGC 5253 as seen with MUSE-NFM: nitrogen enrichment through stellar chemical feedback at parsec scales

Abstract: NGC 5253 is a nearby (D=3.6 Mpc) Blue Compact Dwarf galaxy, notable for its three massive young super star clusters (SSCs) and nitrogen enrichment. Its similarity to extreme star-forming galaxies at high redshift makes it a good local analogue for studying chemical enrichment at high spatial resolution. We characterise the ionised gas and dust in the giant HII region in the proximity of the three SSCs in the centre of NGC 5253 using new Multi-Unit Spectroscopic Explorer Narrow Field Mode adaptive optics-assisted data at unprecedented spatial resolution of 0."15$\sim$2.3 pc. We derive the attenuation for the central SSCs and, for the first time, map the extinction parameter ($R_V$) in an extragalactic object. $R_V$ varies among SSCs, suggesting differences in dust physics. Electron temperature and density diagnostics yield flat temperature distributions $T_\mathrm{e,median}$([NII])$=12000 \pm 1700$ K and $T_\mathrm{e,median}$([SIII])$ = 11000 \pm 600$ K, and a structured $n_e$([SII]) of maximum $1930 \pm 40$ cm$^{-3}$. The direct method gives a flat helium abundance ($10^3y^+ = 81 \pm 4$) and uniform oxygen abundance ($12 + \log(\text{O/H}) = 8.22 \pm 0.05$). N/O shows a factor 2-3 enhancement around the SSCs, mapped here for the first time at such high spatial resolution. The total excess nitrogen mass is $\sim$0.3 $M_\odot$, which we estimate is producible by the observed WN-type Wolf-Rayet (WR) stars. Because there is no direct spatial overlap between the enrichment and WR star positions, the N-rich material appears to have been expelled from the original sites.