Detection of spatial correlations of fundamental plane residuals, and
  cosmological implications
  The fundamental plane (FP) is a widely used tool to investigate the
properties of early-type galaxies, and the tight relation between its
parameters has spawned several cosmological applications, including its use as
a distance indicator for peculiar velocity surveys and as a means to suppress
intrinsic noise in cosmic size magnification measurements. Systematic trends
with the large-scale structure across the FP could cause serious biases for
these cosmological probes, but may also yield new insights into the early-type
population. Here we report the first detection of spatial correlations among
offsets in galaxy size from an FP that explicitly accounts for redshift trends,
using a sample of about $95,000$ elliptical galaxies from the Sloan Digital Sky
Survey. We show that these offsets correlate with the density field out to at
least $10h^{-1}$Mpc at $4\sigma$ significance in a way that cannot be explained
by systematic errors in galaxy size estimates. We propose a physical
explanation for the correlations by dividing the sample into central,
satellite, and field galaxies, identifying trends for each galaxy type
separately. Central (satellite) galaxies lie on average above (below) the FP,
which we argue could be due to a higher (lower) than average mass-to-light
ratio. We fit a simple model to the correlations of FP residuals and use it to
predict the impact on peculiar velocity power spectra, finding a contamination
larger than $10\,\%$ for $k>0.04\,h/$Mpc. Moreover, cosmic magnification
measurements based on an FP could be severely contaminated over a wide range of
scales by the intrinsic FP correlations.
