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Published November 2012 | Published
Journal Article Open

The 6dF Galaxy Survey: the near-infrared Fundamental Plane of early-type galaxies


We determine the near-infrared Fundamental Plane (FP) for ∼10^4 early-type galaxies in the 6-degree Field Galaxy Survey (6dFGS). We fit the distribution of central velocity dispersion, near-infrared surface brightness and half-light radius with a 3D Gaussian model using a maximum-likelihood method. The model provides an excellent empirical fit to the observed FP distribution and the method proves robust and unbiased. Tests using simulations show that it gives superior results to regression techniques in the presence of significant and correlated uncertainties in all three parameters, censoring of the data by various selection effects and outliers in the data sample. For the 6dFGS J-band sample we find an FP with R_e ∝ σ^(1.52±0.03)_0 I_e^(−0.89±0.01), similar to previous near-infrared determinations and consistent with the H- and K-band FPs once allowance is made for differences in mean colour. The overall scatter in R_e about the FP is σ_r = 29 per cent, and is the quadrature sum of an 18 per cent scatter due to observational errors and a 23 per cent intrinsic scatter. Because of the Gaussian distribution of galaxies in FP space, σ_r is not the distance error, which we find to be σ_d = 23 per cent. Using group richness and local density as measures of environment, and morphologies based on visual classifications, we find that the FP slopes do not vary with environment or morphology. However, for fixed velocity dispersion and surface brightness, field galaxies are on average 5 per cent larger than galaxies in groups or higher density environments, and the bulges of early-type spirals are on average 10 per cent larger than ellipticals and lenticulars. The residuals about the FP show significant trends with environment, morphology and stellar population. The strongest trend is with age, and we speculate that age is the most important systematic source of offsets from the FP, and may drive the other trends through its correlations with environment, morphology and metallicity. These results will inform our use of the near-infrared FP in deriving relative distances and peculiar velocities for 6dFGS galaxies.

Additional Information

© 2012 The Authors. Monthly Notices of the Royal Astronomical Society © 2012 RAS. Accepted 2012 May 29. Received 2012 May 29; in original form 2011 October 24. Article first published online: 30 Oct. 2012. We thank the AAO staff who supported the observations for the 6dFGS on the UK Schmidt Telescope;without their professionalism and dedication, this ambitious survey would not have been possible. 3D visualization was achieved with the S2PLOT programming library (Barnes et al. 2006). We particularly thank Chris Fluke for showing us how to construct the interactive 3D figures that make such a difference to understanding intrinsically multidimensional data sets like the Fundamental Plane. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. We acknowledge support from Australian Research Council (ARC) Discovery Projects Grant (DP-0208876), administered by the Australian National University. CM and JM acknowledge support from ARC Discovery Projects Grant (DP-1092666). CM is also supported by a scholarship from the AAO.

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