The circumnuclear star-forming ring of the barred spiral galaxy NGC 1097 provides a unique laboratory to study star formation under extreme conditions. In this work, we aim to derive the physical properties of the circumnuclear star-forming regions (CNSFRs) using MUSE integral field spectroscopy observations. We identified and analysed a total of 24 individual ionised HII within its ring, which spans from ∼385 pc to ∼1. 3 kpc. Despite the complex nuclear activity, all HII regions were found to be purely photoionised. Directly derived abundances reveal supersolar metallicities, with the highest one exceeding five times the solar value (12+log (S/H) = 7. 875 ± 0. 353, Tₑ (SIII) = 3912 ± 567 K) and representing the highest abundance reported to date. In this high-metallicity regime, we found a break in the ionisation parameter– SII / SIII relation, which can be explained by changes in the ionisation structure and line emissivities, as confirmed by photoionisation models that successfully reproduce the observed emission-line ratios. Our results also indicate that the local gas supply regulates the star formation activity within the ring, with the young stars ionising 8% of the total gas in the ring. Furthermore, our findings support a propagating starburst scenario originating in the galaxy nucleus and extending towards the ends of the bar and into the circumnuclear ring through bar-driven shocks, which is consistent with the results of previous multi-wavelength studies. Finally, we likely detected optical signatures associated with one of the two known jets in this galaxy. This finding, together with the radio core emission previously found at sub-parsec scales, reflects the presence of feedback processes operating even on small galactic disc scales.
Zamora et al. (Wed,) studied this question.
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