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Astron. Astrophys. 321, 343-352 (1997)

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[FORMULA] and [FORMULA] of elliptical galaxies and the initial mass function

L. Angeletti and P. Giannone

Istituto Astronomico, Università 'La Sapienza', Via Lancisi 29, I-00161 Roma, Italy

Received 7 May 1996 / Accepted 7 October 1996


The observed trend of mass-to-light ratio [FORMULA] versus elliptical galaxy mass M has been interpreted in various ways by different authors in recent years. We explore in greater detail than previously done the hypothesis that the mentioned trend can be ascribed to a systematic change of the initial mass function (IMF) with M. We use a three-segment power-law IMF with mass exponents [FORMULA], and [FORMULA] for stellar masses m (in [FORMULA]) in the ranges [FORMULA], [FORMULA], and [FORMULA], respectively. The exponent [FORMULA] is considered as a free parameter in the range [FORMULA], while [FORMULA] and [FORMULA] are determined using relations [FORMULA] versus M and [FORMULA] versus M as constraints. We find that [FORMULA], irrespectively of whether the bottom IMF exponent [FORMULA] varies from a flat to a very steep behaviour. We single out a number of realistic solutions; for all of them d [FORMULA] /dlog [FORMULA]. On the other hand, solutions with [FORMULA], and [FORMULA] variable with M are to be excluded, being at variance with the observed [FORMULA] relationship. We confirm that a variable single-slope IMF is not a very appealing solution since it requires a minimum stellar mass [FORMULA].

Key words: galaxies: elliptical and lenticular - elliptical galaxies: fundamental plane and metallicity

Send offprint requests to: L. Angeletti

© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998