The physical parameters varying along the sequence of early-type galaxies are explored using the Fundamental Plane (FP) correlations in the local universe and in distant clusters. The nearby galaxy samples in the UBVRIK bandpasses are drawn from a new survey (Pahre 1998) and the literature. A distant-independent parameterization of Delta ( log r_eff - 0.32 < mu >_eff ) against log sigma_0 shows that the slope A of the FP relation r_eff ~ sigma_0 (A) < Sigma >_eff(B) increases systematically with wavelength from U to K. A model is constructed to describe this variation of the FP slope, the slope of the Mg_2--sigma_0 relation, and the effects of stellar populations gradients. This model shows that there are systematic variations of up to a factor of three in age and metallicity along the full range of the early-type galaxy sequence (in the sense that the most luminous galaxies are the oldest and the most metal rich), and that a wavelength-independent effect (such as dynamical homology breaking or systematic variations in dark matter content) is required. This model predicts that the slope of the FP evolves: the power-law index A should decrease with redshift. A large sample of > 100 early-type galaxies in six clusters at 0.1<z<0.6 is studied using the K-band FP. The slope of the FP is shown to evolve slowly and systematically with redshift in a manner which is in modest agreement with the model predictions based on nearby galaxies. This occurs despite the appearance that the ``average'' elliptical is evolving passively from a single burst at high redshift. The evolving slope of the FP demonstrates that age variations of up to a factor of two or three exist along the early-type sequence.
American Astronomical Society Meeting Abstracts #192
- Pub Date:
- May 1998