Journal Article

On the origin of the scatter around the Fundamental Plane: correlations with stellar population parameters

A. Gargiulo, C. P. Haines, P. Merluzzi, R. J. Smith, F. La Barbera, G. Busarello, J. R. Lucey, A. Mercurio and M. Capaccioli

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 397, issue 1, pages 75-89
Published in print July 2009 | ISSN: 0035-8711
Published online July 2009 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2009.14801.x
On the origin of the scatter around the Fundamental Plane: correlations with stellar population parameters

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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∼ 50 km s−1. We obtain a best-fitting FP relation re∝σ1.06±0.060I−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 > 100 km s−1 galaxies, the FP relation is re∝σ1.35I−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 0.075 dex and the estimated intrinsic scatter decreases from 0.068 to 0.049 dex. 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.

Keywords: galaxies: abundances; galaxies: ellipticals and lenticular, cD; galaxies: formation; galaxies: fundamental parameters; galaxies: structure

Journal Article.  9480 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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