The Stellar Populations in the Central Parsecs of Galactic Bulges

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 (∼ 8 pc) 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 (& 5× 10 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 AV ≈ 0.4 mag and a stellar metallicity of (1–2.5)Z⊙. We discuss the implications of these results for Based on observations obtained with the Hubble Space Telescope, which is operated by AURA, Inc., under NASA contract NAS5-26555. University of Oxford, Astrophysics, Keble Road, OX13RH Oxford, United Kingdom; [email protected] Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany; [email protected] Physics & Astronomy Department, Ohio University, Athens, OH 45701; [email protected] The Observatories of the Carnegie Institution of Washington, 813 Santa Barbara St., Pasadena, CA 91101-1292; [email protected] Department of Physics & Astronomy, 4129 Frederick Reines Hall, University of California, Irvine, CA 92697-4575; [email protected] Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Strasse 1, D-85741 Garching, Germany; [email protected] Department of Astronomy, University of California, Berkeley, CA 94720-3411; [email protected] Astronomy Department, California Institute of Technology, MS 105-24, Pasadena, CA 91125; [email protected]