A resolved study of the inner regions of nearby galaxies with an excess of young massive stars: missing link in the AGN-starburst connection?

We have selected galaxies with very high levels of H alpha emission (EQW(H alpha) > 700 & Aring;.) in their central regions from the final data release of the MaNGA surv e y. Our study focuses on 14 very well-resolved nearby galaxies with stellar masses in the range 9.5 < log M & lowast;/(Mo) < 11.5. We investigate a variety of procedures for selecting galaxy regions that are likely to harbour excess populations of young massive stars, finding that selection in the 2D space of extinction-corrected H alpha EQW and [S III]/[S II ] line ratio produces the best results. By comparing stacked spectra co v ering these regions with stacked spectra co v ering normal starburst regions with 100 & Aring;< EQW(H alpha) < 200 & Aring;, we obtain the following main results: (1) Clear signatures of excess Wolf- Rayet stars are found in half of the H alpha excess regions, (2) galaxy regions containing excess Wolf-Rayet stars are more often associated with the presence of high-ionization emission lines characteristic of accreting black holes. Excess [Ne III ] is detected in 4 out of 8 of the WR regions and there are tentative [Fe X ] detections in 2 galaxies. (3) Regions of the galaxy with excess Wolf-Rayet stars are located where the interstellar medium has larger ionized gas turbulent velocities and higher neutral gas o v erdensities. We make a first attempt to constrain changes in the high-mass end of the stellar initial mass function (IMF) using the HR-pyPopStar evolutionary population synthesis models that include high-wavelength-resolution theoretical atmosphere libraries for Wolf-Rayet stars.