Mon. Not. R. Astron. Soc., 397, 75-89 (2009/July-3)
On the origin of the scatter around the fundamental plane: correlations with stellar population parameters.
GARGIULO A., HAINES C.P., MERLUZZI P., SMITH R.J., LA BARBERA F., BUSARELLO G., LUCEY J.R., MERCURIO A. and CAPACCIOLI M.
Abstract (from CDS):
We present a Fundamental Plane (FP) analysis of 141 early-type galaxies in the Shapley supercluster at z = 0.049 based on spectroscopy from the AAOmega spectrograph at the Anglo-Australian Telescope and photometry from the WFI on the European Southern Observatory/MPI 2.2-m telescope. The key feature of the survey is its coverage of low-mass galaxies down to σ ∼ 50km/s. We obtain a best-fitting FP relation re∝ σ1.06±0.060<I>–0.82±0.02e in the R band. The shallow exponent of σ0 is a result of the extension of our sample to low velocity dispersions. Considering the subsample of σ0> 100km/s galaxies, the FP relation is re∝ σ1.35 <I>–0.81e, consistent with previous studies in the high-luminosity regime. We investigate the origin of the intrinsic FP scatter, using estimates of age, metallicity and α/Fe. We find that the FP residuals anticorrelate (>3σ) with the mean stellar age in agreement with previous work. However, a stronger (>4σ) correlation with α/Fe is also found. These correlations indicate that galaxies with effective radii smaller than those predicted by the FP have stellar populations systematically older and with α overabundances larger than average, for their σ. Including α/Fe as a fourth parameter in the FP, the total scatter decreases from 0.088 to 0.075dex and the estimated intrinsic scatter decreases from 0.068 to 0.049dex. Thus, variations in α/Fe account for ∼30 per cent of the total variance around the FP, and ∼50 per cent of the estimated intrinsic variance. This result indicates that the distribution of galaxies around the FP are tightly related to the enrichment, and hence to the time-scale of star formation. Our results appear to be consistent with the merger hypothesis for the formation of ellipticals which predicts that a significant fraction of the scatter is due to variations in the importance of dissipation in forming merger remnants of a given mass.
© 2009 The Authors. Journal compilation © 2009 RAS
galaxies: abundances - galaxies: ellipticals and lenticular, cD - galaxies: formation - galaxies: fundamental parameters - galaxies: structure
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<Available at CDS (J/MNRAS/397/75): table2.dat>
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