Abstract
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.
Highlights
Large-scale structure cosmology has moved beyond the basic measurement of galaxy positions used for example to infer galaxy clustering and baryon acoustic oscillations
5.2 fundamental plane (FP) residual size correlations In Fig. 4 we show results for the spatial correlations of FP residuals λ using the statistics ∆gg, wgλ, and wλλ as defined in Sect
We propose a simplistic model for the spatial correlations of the FP residuals, assuming that λ is proportional to the matter density contrast, δ, λ(x) := B δ(x)
Summary
Large-scale structure cosmology has moved beyond the basic measurement of galaxy positions used for example to infer galaxy clustering and baryon acoustic oscillations. Mapping out the peculiar velocity field (e.g., Springob et al 2014) is another example of the exploitation of the FP for the purposes of a cosmological probe (see Strauss & Willick 1995 for a review) Both applications involve measuring the observed galaxy size, and predicting a galaxy size based on the FP. Mandelbaum between the prediction and observation is used to measure the quantity of interest, either the size change due to lensing magnification, or the line-of-sight peculiar velocity, which modifies the redshift and the angular diameter distance used to translate an angular size to a physical size Both of these cosmological probes make the important fundamental assumption that deviations in galaxy sizes from the FP relation do not have some underlying correlation with the large-scale distribution of matter, other than the one induced by the cosmological signal.
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