Ages and metallicities of circumnuclear star formation regions from Gemini IFU observations

Abstract

Aims. We derive the age and metallicity of circumnuclear star formation regions (CNSFRs) located in the spiral galaxies NGC6951 and NGC1097 and investigate the cause of the very low equivalent widths of emission lines found for these regions. Methods. We used optical two-dimensional spectroscopic data obtained with Gemini GMOS-IFUs and a grid of photoionization models to derive the the metallicities and ages of CNSFRs. Results. We find star formation rates in the range 0.002–0.14 Mʘ yr-ˡ and oxygen abundance of 12 + log(O/H) ≈ 8.8 dex, similar to those of most metal-rich nebulae located in the inner region of galactic disks. Conclusions. We conclude that the very low emission-line equivalent widths observed in CNSFRs are caused by the “contamination” of the continuum by (1) contribution of the underlying bulge continuum combined with (2) contribution from previous episodes of star formation at the CNSFRs.