Gemini NIFS survey of feeding and feedback processes in nearby Active Galaxies: VI -- Stellar Populations

TL;DR

This study maps stellar populations in 18 nearby Seyfert galaxies' nuclei, revealing young to intermediate stars, correlations with AGN activity, and suggesting a rejuvenation process influenced by the AGN's feedback.

Contribution

First detailed near-infrared integral field spectroscopic analysis of stellar populations in the nuclear regions of Seyfert galaxies, linking stellar ages with AGN properties.

Findings

Young to intermediate stellar populations dominate the nuclear light.

Correlations between X-ray luminosity and dust, continuum, and reddening.

Evidence of a delay between star formation and AGN activity.

Abstract

We use Gemini Near-Infrared Integral Field Spectrograph (NIFS) adaptive optics assisted data-cubes to map the stellar population of the inner few hundred parsecs of a sample of 18 nearby Seyfert galaxies. The near-infrared light is dominated by the contribution of young to intermediate old stellar populations, with light-weighted mean ages $<t>_L\ \lesssim $ 1.5\,Gyr. Hot dust ($HD$) emission is centrally peaked (in the unresolved nucleus), but it is also needed to reproduce the continuum beyond the nucleus in nearly half of the sample. We have analysed the stellar population properties of the nuclear region and their relation with more global properties of the galaxies. We find a correlation between the X-ray luminosity and the contributions from the $HD$, featureless continuum $FC$ and reddening $A_V$. We attribute these correlations to the fact that all these properties are linked to the mass accretion rate to the active galactic nuclei (AGN). We also find a correlation of the bolometric luminosity $log(LBol_{obs})$ with the mass-weighted mean age of the stellar population, interpreted as due a delay between the formation of new stars and the triggering/feeding of the AGN. The gas reaching the supermassive black hole is probably originated from mass loss from the already somewhat evolved intermediate-age stellar population ($<t>_L \lesssim $ 1.5\,Gyr). In summary, our results show that there is a significant fraction of young to intermediate age stellar populations in the inner few 100\,pc of active galaxies, suggesting that this region is facing a rejuvenation process in which the AGN, once triggered, precludes further star formation, in the sense that it can be associated with the lack of new star formation in the nuclear region.