The stellar content of elliptical nuclei

TLDR: In this article, it has been shown that the source of the excess UV light is not young OB stars, but rather a large number of old stellar populations in elliptical galaxies.

Abstract: New developments in understanding the stellar populations of ! elliptical nuclei are discussed. Variations in iron-peak spectral j features have recently been detected, which are much smaller than \\ changes in CN, Mg, and Na. A study is presently in progress to I determine whether this pattern is consistent with lockstep enhancements j in all heavy elements. Present evidence on the ultraviolet spectra of | ellipticals now suggests that the source of the excess UV light is not I young OB stars. A new correlation is also pointed out between UV j excess and mean line strength. If real, this trend is further evidence j against significant numbers of young OB stars in elliptical galaxies. j To first approximation, only two physical parameters are needed to j characterize the spectra of old stellar populations, namely stellar I age (or rate of star formation versus time) and composition. My j remarks today concern these two quantities as they apply to ellipticalI galaxy populations. Consider composition first. It has long been known that E-galaxy spectra exhibit a sequence in line strength and color, exemplified both by variations among galaxies and by radial gradients within j galaxies. As with the phenomenologically similar trend among globular \\ clusters, this sequence has conventionally been interpreted in terms of metallicity variations. Attempts to calibrate the sequence in terms of iron abundance have typically shown that the strongest-lined ellipticals are between two and four times more metal-rich than M32 (Faber 1973; Oke and Schwarzschild 1975; Larson and Tinsley 1974; Cohen 1979). A weakness of these previous calibrations, however, is the fact that they depend largely on the very large line-strength changes seen only in CN, Mg, and Na. No iron-peak features have as yet been used. Counter to the usual metallicity interpretation, a few authors have proposed instead that only the elements N, Mg, and Na are changing