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