Low Redshift Baryon Acoustic Oscillation Measurement from the Reconstructed 6-degree Field Galaxy Survey

TL;DR

This paper re-evaluates low redshift BAO measurements from the 6dFGS survey using improved methods, providing robust distance constraints that support standard cosmology and inform Hubble constant estimates.

Contribution

It presents a new analysis of 6dFGS BAO data using density field reconstruction and mock-based covariance, resulting in the most robust low-redshift BAO constraints to date.

Findings

Measured D_V at z=0.097: 372±17 Mpc

Combined BAO measurement at z=0.122: 539±17 Mpc

Consistent with ΛCDM and Planck priors on Ω_mh^2

Abstract

Low redshift measurements of Baryon Acoustic Oscillations (BAO) test the late time evolution of the Universe and are a vital probe of Dark Energy. Over the past decade both the 6-degree Field Galaxy Survey (6dFGS) and Sloan Digital Sky Survey (SDSS) have provided important distance constraints at $z < 0.3$. In this paper we re-evaluate the cosmological information from the BAO detection in 6dFGS making use of HOD populated COLA mocks for a robust covariance matrix and taking advantage of the now commonly implemented technique of density field reconstruction. For the 6dFGS data, we find consistency with the previous analysis, and obtain an isotropic volume averaged distance measurement of $D_{V}(z_{\mathrm{eff}}=0.097) = 372\pm17(r_{s}/r_{s}^{\mathrm{fid}})\,\mathrm{Mpc}$, which has a non-Gaussian likelihood outside the $1\sigma$ region. We combine our measurement from both the post-reconstruction clustering of 6dFGS and SDSS MGS offering the most robust constraint to date in this redshift regime, $D_{V}(z_{\mathrm{eff}}=0.122)=539\pm17(r_{s}/r^{\mathrm{fid}}_{s})\,\mathrm{Mpc}$. These measurements are consistent with standard $\Lambda\mathrm{CDM}$ and after fixing the standard ruler using a Planck prior on $\Omega_{m}h^{2}$, the joint analysis gives $H_{0}=64.0\pm3.5\,\mathrm{kms}^{-1}\mathrm{Mpc}^{-1}$. In the near future both the Taipan Galaxy Survey and the Dark Energy Spectroscopic Instrument (DESI) will improve this measurement to $1\%$ at low redshift.