Cosmicflows-2: The Data (1307.7213v1)

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.

• The paper presents an extensive dataset of over 8000 galaxy distances and peculiar velocities using varied astronomical measurement techniques.
• It employs rigorous cross-calibration methods, including Cepheid and TRGB, to standardize data from TFR, FP, SBF, and SNIa observations.
• It reports a derived Hubble Constant of 74.4 ± 3.0 km/s/Mpc, providing significant insights for precision cosmology and large-scale structure studies.

Overview of "Cosmicflows-2: The Data"

The paper "Cosmicflows-2: The Data", authored by R. Brent Tully et al., presents an extensive database of galaxy distances and peculiar velocities, with compilations from a variety of astronomical measurement techniques. This dataset, known as Cosmicflows-2 (CF2), is an expanded version of its predecessor Cosmicflows-1 (CF1), aiming to provide a comprehensive tool for the paper of large-scale cosmic flows and structure formation in the universe. The authors meticulously combine data from different methodologies, ensuring a standardized scale across all data sources. This document provides a detailed summary of the methodologies, data integration, results, and implications of this expansive work.

Methodologies and Data Collection

CF2 comprises distances derived from over 8000 galaxies employing diverse methodologies including:

1. Tully-Fisher Relation (TFR) - The primary technique used, accounting for a substantial portion of the dataset. The authors present an improved maximum rotation velocity measure using HI linewidths ($W_{m50}$) and photometric data, especially in the $I$ band and Spitzer [3.6] band.
2. Fundamental Plane (FP) Method - Used predominantly for early-type galaxies.
3. Surface Brightness Fluctuation (SBF) Method - Primarily applicable to galaxy groups, providing vital distance measures toward clusters.
4. Cepheid Period-Luminosity Relation (Cepheid PLR) and Tip of the Red Giant Branch (TRGB) - These provide the foundational zero point calibration for the database, especially critical for nearby galaxies.
5. Type Ia Supernovae (SNIa) - Provides highly accurate distance measures, integrated into the CF2 through cross-calibration with the TFR method.
6. Miscellaneous Methods - Includes methodologies like RR Lyrae, Eclipsing Binary, and Maser distance measures.

The authors emphasize the importance of ensuring uniformity across these varied techniques. To maintain consistency, each method was aligned with the established zero-point scale using Cepheid and TRGB calibrations.

Integration and Calibration

The CF2 data compilation aims to construct a coherent framework to support velocity field studies by integrating observational data from multiple telescopes and techniques. The datasets were harmonized to ensure a standard distance scale, emphasizing the importance of a consistent zero-point across methodologies. While TFR constitutes the majority of the data set, the other techniques, particularly SBF and SNIa, are crucial for refining the distance scale and providing checks and balances against the TFR measures. The practical scale was further refined by integrating recent observations with Spitzer and WISE photometry at mid-infrared bands, which offered advantages of consistency and reduced obscuration effects.

Results

The data analysis confirmed the consistency of the methodologies with a derived Hubble Constant of H$_0 = 74.4$ ± 3.0 km s$^{-1}$ Mpc$^{-1}$ based on fits to the velocity data for galaxies at redshifts $0.013 < z < 0.1$. This value has significant implications for the precision cosmology field, providing constraints on dark energy properties and cosmological parameters. While consistent with other direct measurements, this value notably contrasts with results derived from CMB observations by Planck, provoking further discussion and research into model-specific predictions.

Implications and Future Work

CF2 represents a substantial advancement for the paper of cosmic velocity fields, particularly on local scales where peculiar velocities significantly impact the understanding of cosmic structures. The data set supports precision efforts toward mapping the universe's large-scale structures, offering insights into density fields and underlying dark matter distributions.

Looking forward, CF2 data could drive further theoretical modeling and simulations that focus on the dynamics of galaxy movements and the gravitational influence of large-scale structures. Additionally, this compilation serves as a robust platform for future datasets that may incorporate new techniques or refined older methods. Potential applications extend into refining the cosmic distance ladder and creating accurate models of universe expansion.

Overall, Cosmicflows-2 is an instrumental contribution to cosmography, offering a high-resolution view of the local universe and informing a variety of astrophysical and cosmological explorations. Its integration with upcoming observational campaigns and theoretical work will continue to shed light on the fundamental questions of cosmic structure and evolution.