Low redshift Baryon Acoustic Oscillation measurement from the reconstructed 6-degree Field Galaxy Survey

Low-redshift measurements of baryon acoustic oscillations (BAO) measure 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 Main Galaxy Sample (SDSS MGS) 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 halo occupation distribution (HOD)-populated COmoving Lagrangian Acceleration (COLA) mocks for an accurate covariance matrix and take 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 DV(zeff=0.097)=[372±17(±9833)](rs/rfids)Mpc but with a highly non-Gaussian likelihood. We combine our measurement from both the post-reconstruction clustering of 6dFGS and SDSS MGS offering an updated constraint in this redshift regime, DV(zeff=0.122)=[539±17(±3539)](rs/rfids)Mpc⁠. This measurement tightens the constraint in comparison to the result from SDSS MGS alone, especially at the 2σ and higher significance levels. These measurements are consistent with standard Λcold dark matter (ΛCDM) and after fixing the standard ruler using a Planck prior on Ωmh2, the joint analysis gives H0=64.0±3.5kms−1Mpc−1⁠. This result is consistent with other BAO and Cosmic microwave background (CMB) studies but is in >2σ tension with supernova distance ladder measurements. 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.