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

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.