The Stellar Populations in the Central Parsecs of Galactic Bulges Central Stellar Populations

TL;DR

This study analyzes the stellar populations in the central regions of 23 nearby disk galaxies using Hubble spectra, revealing predominantly old stars with some younger components, and discusses implications for black hole environments.

Contribution

It provides detailed stellar population analysis of galaxy nuclei using spectral modeling, highlighting the age distribution and metallicity of stars in these regions.

Findings

Majority (~80%) of nuclei have old (>5 Gyr) stellar populations.

Approximately 25% show evidence of younger (<1 Gyr) stars.

Results support accretion-powered activity in Seyfert and LINER nuclei.

Abstract

We present Hubble Space Telescope blue spectra at intermediate spectral resolution for the nuclei of 23 nearby disk galaxies. These objects were selected to have nebular emission in their nuclei, and span a range of emission-line classifications as well as Hubble types. In this paper we focus on the stellar population as revealed by the continuum spectral energy distribution measured within the central 0."13 (~8pc) of these galaxies. The data were modeled with linear combinations of single-age stellar population synthesis models. The large majority (~80%) of the surveyed nuclei have spectra whose features are consistent with a predominantly old (>5x10^9 yr) stellar population. Approximately 25% of these nuclei show evidence of a component with age younger than 1 Gyr, with the incidence of these stars related to the nebular classification. Successful model fits imply an average reddening corresponding to A_V~0.4 mag and stellar metallicity of (1--2.5) Z_sun. We discuss the implications of these results for the understanding of star formation history in the environment of quiescent and active supermassive black holes. Our findings reinforce the picture wherein Seyfert nuclei and the majority of low-ionization nuclear emission-line regions (LINERs) are predominantly accretion-powered, and suggest that much of the central star formation in Hii nuclei is actually circumnuclear.