The 6dF Galaxy Survey: The Near-Infrared Fundamental Plane of Early-Type Galaxies

We determine the near-infrared Fundamental Plane (FP) for $sim10^4$ early-type galaxies in the 6dF Galaxy Survey (6dFGS). We fit the distribution of central velocity dispersion, near-infrared surface brightness and half-light radius with a three-dimensional Gaussian model using a maximum likelihood method. For the 6dFGS $J$ band sample we find a FP with $R_{e}$,$propto$,$sigma_0^{1.52pm0.03}I_{e}^{-0.89pm0.01}$, similar to previous near-IR determinations and consistent with the $H$ and $K$ band Fundamental Planes once allowance is made for differences in mean colour. The overall scatter in $R_e$ about the FP is $sigma_r$,=,29%, and is the quadrature sum of an 18% scatter due to observational errors and a 23% intrinsic scatter. Because of the distribution of galaxies in FP space, $sigma_r$ is not the distance error, which we find to be $sigma_d$,=,23%. 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% larger than galaxies in higher-density environments, and the bulges of early-type spirals are on average 10% 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.

The SAMI Galaxy Survey: stellar population and structural trends across the Fundamental Plane

We study the Fundamental Plane (FP) for a volume- and luminosity-limited sample of 560 early-type galaxies from the SAMI survey. Using r-band sizes and luminosities from new Multi-Gaussian Expansion (MGE) photometric measurements, and treating luminosity as the dependent variable, the FP has coefficients a=1.294$pm$0.039, b= 0.912$pm$0.025, and zero-point c= 7.067$pm$0.078. We leverage the high signal-to-noise of SAMI integral field spectroscopy, to determine how structural and stellar-population observables affect the scatter about the FP. The FP residuals correlate most strongly (8$sigma$ significance) with luminosity-weighted simple-stellar-population (SSP) age. In contrast, the structural observables surface mass density, rotation-to-dispersion ratio, Sersic index and projected shape all show little or no significant correlation. We connect the FP residuals to the empirical relation between age (or stellar mass-to-light ratio $Upsilon_star$) and surface mass density, the best predictor of SSP age amongst parameters based on FP observables. We show that the FP residuals (anti-)correlate with the residuals of the relation between surface density and $Upsilon_star$. This correlation implies that part of the FP scatter is due to the broad age and $Upsilon_star$ distribution at any given surface mass density. Using virial mass and $Upsilon_star$ we construct a simulated FP and compare it to the observed FP. We find that, while the empirical relations between observed stellar population relations and FP observables are responsible for most (75%) of the FP scatter, on their own they do not explain the observed tilt of the FP away from the virial plane.

Improved strong lensing modelling of galaxy clusters using the Fundamental Plane: the case of Abell S1063

From Hubble Frontier Fields photometry, and data from the Multi Unit Spectroscopic Explorer on the Very Large Telescope, we build the Fundamental Plane (FP) relation for the early-type galaxies of the cluster Abell S1063. We use this relation to develop an improved strong lensing model of the total mass distribution of the cluster, determining the velocity dispersions of all 222 cluster members included in the model from their measured structural parameters. Fixing the hot gas component from X-ray data, the mass density distributions of the diffuse dark matter haloes are optimised by comparing the observed and model-predicted positions of 55 multiple images of 20 background sources, distributed over the redshift range $0.73-6.11$. We determine the uncertainties on the model parameters with Monte Carlo Markov chains. Compared to previous works, our model allows for the inclusion of a scatter on the relation between the total mass and the velocity dispersion of cluster members, which also shows a shallower slope. We notice a lower statistical uncertainty on the value of some parameters, such as the core radius, of the diffuse mass component of the cluster. Thanks to a new estimate of the stellar mass of all members, we measure the projected, cumulative mass profiles out to a radius of 350 kpc, for all baryonic and dark matter components of the cluster. At the outermost radius, we find a baryon fraction of $0.147 pm 0.002$. We compare the sub-haloes as described by our model with recent hydrodynamical cosmological simulations. We find good agreement in terms of stellar mass fraction. On the other hand, we report some discrepancies in terms of maximum circular velocity, which is an indication of their compactness, and sub-halo mass function in the central cluster regions.

The 6dF Galaxy Survey: Samples, Observational Techniques and the First Data Release

The 6dF Galaxy Survey (6dFGS) aims to measure the redshifts of around 150,000 galaxies, and the peculiar velocities of a 15,000-member sub-sample, over almost the entire southern sky. When complete, it will be the largest redshift survey of the nearby universe, reaching out to about z ~ 0.15, and more than an order of magnitude larger than any peculiar velocity survey to date. The targets are all galaxies brighter than K_tot = 12.75 in the 2MASS Extended Source Catalog (XSC), supplemented by 2MASS and SuperCOSMOS galaxies that complete the sample to limits of (H, J, r_F, b_J) = (13.05, 13.75, 15.6, 16.75). Central to the survey is the Six-Degree Field (6dF) multi-fibre spectrograph, an instrument able to record 150 simultaneous spectra over the 5.7-degree field of the UK Schmidt Telescope. An adaptive tiling algorithm has been employed to ensure around 95% fibering completeness over the 17046 sq.deg of the southern sky with | b | > 10 deg. Spectra are obtained in two observations using separate V and R gratings, that together give R ~ 1000 over at least 4000 -- 7500 Angstroms and signal-to-noise ratio ~10 per pixel. The 6dFGS database is available at http://www-wfau.roe.ac.uk/6dFGS/, with public data releases occuring after the completion of each third of the survey.