The 6dF Galaxy Survey: Final Redshift Release (DR3) and Southern Large-Scale Structures (0903.5451v1)

Abstract: We report the final redshift release of the 6dF Galaxy Survey, a combined redshift and peculiar velocity survey over the southern sky (|b|>10 deg). Its 136,304 spectra have yielded 110,256 new extragalactic redshifts and a new catalogue of 125,071 galaxies making near-complete samples with (K, H, J, r_F, b_J) <= (12.65, 12.95, 13.75, 15.60, 16.75). The median redshift of the survey is 0.053. Survey data, including images, spectra, photometry and redshifts, are available through an online database. We describe changes to the information in the database since earlier interim data releases. Future releases will include velocity dispersions, distances and peculiar velocities for the brightest early-type galaxies, comprising about 10% of the sample. Here we provide redshift maps of the southern local universe with z<=0.1, showing nearby large-scale structures in hitherto unseen detail. A number of regions known previously to have a paucity of galaxies are confirmed as significantly underdense regions. The URL of the 6dFGS database is http://www-wfau.roe.ac.uk/6dFGS

• The paper presents the final release of 125,071 extragalactic redshifts, including 110,256 newly measured entries.
• It employs refined methodologies integrating 2MASS and SuperCOSMOS data to enhance redshift accuracy and spectral calibrations.
• The study reveals detailed southern large-scale structures, delineating superclusters, filaments, and voids to refine cosmological models.

Analysis of the 6dF Galaxy Survey: Final Redshift Release and Large-Scale Structures

The 6dF Galaxy Survey (6dFGS) presents a comprehensive redshift and peculiar velocity survey covering the majority of the southern sky, achieving a notable milestone with the final release of 125,071 extragalactic redshifts, out of which 110,256 are newly secured by the survey. The survey, conducted over nearly 17,000 square degrees, encompasses a wide angular swath and depth, with a median redshift of 0.053, thereby marking it as the most extensive and deep hemispheric redshift survey to date.

Survey Methodology and Data Enhancements

The data acquisition, spanning from May 2001 to January 2006, involved meticulous observations using the Six Degree Field (6dF) multi-object spectrograph at the UK Schmidt Telescope. The survey employed a strategic selection of galaxies primarily based on near-infrared magnitudes derived from the 2MASS Extended Source Catalog and optical data from SuperCOSMOS, resulting in an impressive sample size with high completeness in the primary NIR bands.

The data release introduces a gamut of revisions and enhancements to previous interim releases, refining the spectroscopic data quality and accuracy. This includes precise redshift recalibrations, reductions in fibre cross-talk contamination, and corrections for systematic errors like slit vane shifts detected in early operations. Further, the integration of revised 2MASS and SuperCOSMOS photometric data significantly improves the reliability of magnitude-based selection and subsequent analysis.

Findings and Implications on Large-Scale Structure

The survey's data visualization unveils the intricate large-scale structure of the southern low-redshift universe in unprecedented depth. Prominent amongst these features are the Shapley and Hydra-Centaurus superclusters, alongside myriad interconnecting filaments and expansive voids that challenge previous perceptions of cosmic homogeneity. The 6dFGS delineates these structures with remarkable clarity, furnishing critical insights into the spatial distribution of large-scale cosmic matter as well as typical and atypical voids within the surveyed volume.

The survey's extensive dataset reinforces past findings from earlier surveys such as the 2dF Galaxy Redshift Survey and SDSS, yet extends well beyond their reach by virtue of its comprehensive angular coverage. The delineation of such cosmic structures not only bolsters our understanding of large-scale galaxy distribution but also aids in refining cosmological models, especially concerning the $\Lambda$CDM paradigm.

Future Prospects and Utilization

The reach of 6dFGS data transcends mere mapping, positioning itself as a valuable resource for subsequent studies into cosmic flows, galaxy formation, and evolutionary dynamics. It sets a foundational precedent for future surveys like those anticipated with the SKA and ASKAP, which promise to further unravel the interrelations between baryonic and dark matter across larger cosmic volumes.

Ongoing and future analyses will likely focus on leveraging this data to parse finer subtleties within the cosmic web, unravel peculiar velocities, and improve constraints on cosmological parameters. As these studies mature, the legacy of the 6dF Galaxy Survey will resonate prominently as a cornerstone in the field of extragalactic astronomy and cosmology.