The VIMOS Public Extragalactic Redshift Survey (VIPERS): An unbiased estimate of the growth rate of structure at $\mathbf{\left<z\right>=0.85}$ using the clustering of luminous blue galaxies

TL;DR

This study uses VIPERS data to assess how selecting luminous blue galaxies as tracers minimizes systematic errors in measuring the growth rate of cosmic structure at redshift 0.85, achieving high accuracy with non-linear modeling.

Contribution

It demonstrates that selecting luminous blue galaxies optimizes the measurement of the growth rate by reducing non-linear effects and systematic errors compared to other galaxy samples.

Findings

Systematic error in $f\sigma_8$ is below 1-2% with luminous blue galaxies.

Selection of luminous blue galaxies maximizes the fraction of central objects, reducing non-linear contributions.

Measured $f\sigma_8$ at $0.85$ is $0.45 \pm 0.11$, consistent with cosmological models.

Abstract

We use the VIPERS final data release to investigate the performance of colour-selected populations of galaxies as tracers of linear large-scale motions. We empirically select volume-limited samples of blue and red galaxies as to minimise the systematic error on the estimate of the growth rate $f\sigma_8$ from the anisotropy of the two-point correlation function. To this end, rather than rigidly splitting the sample into two colour classes we define the red/blue fractional contribution of each object through a weight based on the $(U-V)$ colour distribution. Using mock surveys that are designed to reproduce the observed properties of VIPERS galaxies, we find the systematic error in recovering the fiducial value of $f\sigma_8$ to be minimized when using a volume-limited sample of luminous blue galaxies. We model non-linear corrections via the Scoccimarro extension of the Kaiser model, finding systematic errors on $f\sigma_8$ of below $1-2\%$, using scales as small as 5 $h^{-1}\mathrm{Mpc}$. We interpret this result as indicating that selection of luminous blue galaxies maximises the fraction that are central objects in their dark matter haloes; this in turn minimises the contribution to the measured $\xi(r_p,\pi)$ from the 1-halo term, which is dominated by non-linear motions. The gain is inferior if one uses the full magnitude-limited sample of blue objects, consistent with the presence of a significant fraction of blue, fainter satellites dominated by non-streaming, orbital velocities. We measure a value of $f\sigma_8=0.45 \pm 0.11$ over the single redshift range $0.6\le z\le 1.0$, corresponding to an effective redshift for the blue galaxies $\left<z\right>=0.85$. Including in the likelihood the potential extra information contained in the blue-red galaxy cross-correlation function does not lead to an appreciable improvement in the error bars, while it increases the systematic error.