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

TL;DR

This study investigates the inner regions of nearby galaxies with excess young massive stars, revealing links between Wolf Rayet stars, black hole activity, and interstellar medium conditions, advancing understanding of the AGN-starburst connection.

Contribution

It introduces a new method for selecting starburst regions and provides observational evidence connecting Wolf Rayet stars with black hole activity and interstellar medium properties.

Findings

Excess Wolf Rayet stars are found in half of the Hα excess regions.

Regions with Wolf Rayet stars often show high-ionization emission lines linked to black holes.

Galactic regions with Wolf Rayet stars have higher gas turbulence and density.

Abstract

We have selected galaxies with very high levels of H$\alpha$ emission (EQW(H$\alpha$)$>$700 \AA.) in their central regions from the final data release of the MaNGA survey . Our study focuses on 14 very well-resolved nearby galaxies with stellar masses in the range $9.5 < \log M_*/(M_{\odot}) < 11.5$. 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 2-dimensional space of extinction-corrected H$\alpha$ EQW and [SIII]/[SII] line ratio produces the best results. By comparing stacked spectra covering these regions with stacked spectra covering normal starburst regions with 100\AA$<$EQW(H$\alpha$)$<$200\AA, we obtain the following main results: 1) Clear signatures of excess Wolf Rayet stars are found in half of the H$\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 [NeIII] is detected in 4 out of 8 of the WR regions and there are tentative [FeX] 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 overdensities. 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.