Cosmicflows-2: The Data

TL;DR

Cosmicflows-2 compiles over 8000 galaxy distances and velocities, integrating various measurement methods to create a comprehensive, accurate dataset for studying cosmic velocity fields and estimating the Hubble Constant.

Contribution

This paper presents a large, unified dataset of galaxy distances and velocities, emphasizing the integration and calibration of multiple measurement techniques for improved accuracy.

Findings

Distances are consistent with H_0 = 74.4 km/s/Mpc.

The dataset covers local to moderate redshift galaxies with high density.

The compilation enhances velocity field studies and cosmological analyses.

Abstract

Cosmicflows-2 is a compilation of distances and peculiar velocities for over 8000 galaxies. Numerically the largest contributions come from the luminosity-linewidth correlation for spirals, the TFR, and the related Fundamental Plane relation for E/S0 systems, but over 1000 distances are contributed by methods that provide more accurate individual distances: Cepheid, Tip of the Red Giant Branch, Surface Brightness Fluctuation, SNIa, and several miscellaneous but accurate procedures. Our collaboration is making important contributions to two of these inputs: Tip of the Red Giant Branch and TFR. A large body of new distance material is presented. In addition, an effort is made to assure that all the contributions, our own and those from the literature, are on the same scale. Overall, the distances are found to be compatible with a Hubble Constant H_0 = 74.4 +-3.0 km/s/Mpc. The great interest going forward with this data set will be with velocity field studies. Cosmicflows-2 is characterized by a great density and high accuracy of distance measures locally, falling to sparse and coarse sampling extending to z=0.1.