The Stellar Population of NGC 6166

Abstract

New optical and ultraviolet observations were obtained of NGC 6166, a cD galaxy and strong radio source in which both a large cooling flow and ongoing star formation have been detected. The spectrophotometry has been analyzed by a technique of differential spectral synthesis, in which the galaxy spectrum is compared with a spectral sequence composed of normal elliptical galaxies of a range of metal abundances. Both the optical and ultraviolet spectra are best fitted by a combination of metal-rich elliptical plus about four percent (at 5550 A) young population, the latter enriched in early- to mid-O stars by a factor of 20 over that observed in the solar neighborhood. Such a young population corresponds to a star-formation rate of 0.1/sq h within 3.2/h kpc of the center. This rate is consistent with earlier deductions from the optical spectrum but is inconsistent in both the amount and shape of the initial mass function with that required in the cooling flow model.