Evidence of Galaxy Cluster Motions with the Kinematic Sunyaev-Zel'dovich Effect (1203.4219v2)

Abstract: Using high-resolution microwave sky maps made by the Atacama Cosmology Telescope, we for the first time present strong evidence for motions of galaxy clusters and groups via microwave background temperature distortions due to the kinematic Sunyaev-Zel'dovich effect. Galaxy clusters are identified by their constituent luminous galaxies observed by the Baryon Oscillation Spectroscopic Survey, part of the Sloan Digital Sky Survey III. We measure the mean pairwise momentum of clusters, with a probability of the signal being due to random errors of 0.002, and the signal is consistent with the growth of cosmic structure in the standard model of cosmology.

Evidence of Galaxy Cluster Motions with the Kinematic Sunyaev-Zel'dovich Effect

The paper "Evidence of Galaxy Cluster Motions with the Kinematic Sunyaev-Zel'dovich Effect" employs data from the Atacama Cosmology Telescope (ACT) to present the first robust statistical evidence of galaxy cluster motions through the kinematic Sunyaev-Zel'dovich (kSZ) effect. This effect, first described by Sunyaev and Zel'dovich in the early 1970s, refers to distortions in the Cosmic Microwave Background (CMB) caused by the Doppler shift of thermal radiation as it scatters off moving electron clouds in galaxy clusters. By distinguishing between this kSZ effect and the more pronounced thermal Sunyaev-Zel'dovich (tSZ) effect, the paper offers an innovative method to probe the dynamics of galaxy clusters and thus, cosmic structure formation.

Methodology

The analysis utilizes high-resolution 148 GHz microwave maps obtained from ACT, which cover a swath of the sky around the celestial equator with impressive angular resolution. The clusters of interest are located using the luminous galaxies catalogued by the Baryon Oscillation Spectroscopic Survey (BOSS) from the Sloan Digital Sky Survey III (SDSS-III). This dataset provides critical redshift information and serves as a proxy for cluster locations. For each galaxy cluster, the observed CMB temperature anisotropies are interpreted as manifestations of kSZ-induced momentum shifts. Multiple independent measurements are combined statistically, leveraging the mean pairwise momentum estimator to detect relative motions between galaxy clusters. A key strength of this approach lies in its insensitivity to the tSZ signal, offering a unique vantage point for examining cluster dynamics.

Results

The paper reports a detection of galaxy cluster motions with a statistical significance that mischances the signal being a random error at only 0.002 probability. This outcome aligns with expectations from the standard cosmological model, adding credibility to the inferred growth of cosmic structures. The results are obtained by evaluating the mean pairwise momentum of galaxy clusters, derived from ACT's microwave temperature data corrected for redshift-dependent effects. Crucially, the evidence for galaxy cluster motions is observed out to a redshift of 0.8, representing a significant extension over typical optical observations, which are largely limited to local universe studies.

Implications

This finding has profound implications for both cosmology and particle physics. Most notably, it offers an independent and direct confirmation of large-scale cosmic flow patterns as predicted by the Lambda Cold Dark Matter ($\Lambda$CDM) model. Moreover, the kSZ detection provides constraints on large-scale velocity fields, contributing to a deeper understanding of the standard cosmological model. It also potentially aids in resolving the missing baryon problem by correlating observed baryon content in clusters with theoretical predictions. Looking forward, enhanced analyses of the kSZ effect could refine methodologies for constraining cosmic growth and testing alternative gravity models.

Future Directions

Future research will likely involve the integration of more extensive survey data, including forthcoming results from the Planck satellite and other CMB observatories. Such data can refine kSZ effect measurements, aiding the development of increasingly precise models of galaxy cluster dynamics and growth. Anticipated improvements in microwave background measurement techniques and the deployment of large optical surveys, like the LSST, promise richer datasets for cosmological parameter constraints. Additionally, further paper of the baryon fraction in galaxy clusters using the kSZ effect could illuminate the distribution of dark matter and insights into the nature of dark energy.

In summary, the paper demonstrates the potential of the kinematic Sunyaev-Zel'dovich effect as a powerful tool for probing the motions and mass distributions of galaxy clusters. It lays the groundwork for a new observational paradigm, offering insights into the dynamics of the universe on its largest scales.