Central oxygen abundances in the spiral galaxies of the MaNGA survey: Galaxies with central starbursts

Abstract: We examine whether there are deviations of the local central oxygen abundances in spiral galaxies from the general metallicity gradients. We compare the values of the central intersect oxygen abundances estimated from the metallicity gradient based on the integral field unit (IFU) spectroscopy from the Mapping Nearby Galaxies at the Apache Point Observatory (MaNGA) survey and the local central oxygen abundances obtained from the single-fibre observations from the Sloan Digital Sky Survey (SDSS). Special attention is placed on galaxies with recent and currently ongoing central starbursts (cSB galaxies). We selected a sample of 30 cSB galaxies from our total sample of 381 MaNGA galaxies, using the decrease in the Dn4000 index (a stellar age indicator) in the circumnuclear region as the selection criterion. We found that the local central oxygen abundances follow the general metallicity gradients in the galaxies well and agree with the central intersect abundances within uncertainties of the central abundances determinations. Starbursts in the centres of cSB galaxies do not produce noticeable oxygen enrichments. The central starbursts imply that an appreciable amount of gas is present at the centres of cSB galaxies. The gas at the centre of galaxy can serve not only as a raw material for the star formation, but also as a fuel for the activity of the galactic nucleus (AGN). We found that the AGN is the main source of the ionising radiation at the centres of six cSB galaxies in our sample.