Galaxy Clusters Selected with the Sunyaev-Zel'dovich Effect from 2008 South Pole Telescope Observations (1003.0003v2)

Abstract: We present a detection-significance-limited catalog of 21 Sunyaev-Zel'dovich selected galaxy clusters. These clusters, along with 1 unconfirmed candidate, were identified in 178 deg^2 of sky surveyed in 2008 by the South Pole Telescope to a depth of 18 uK-arcmin at 150 GHz. Optical imaging from the Blanco Cosmology Survey (BCS) and Magellan telescopes provided photometric (and in some cases spectroscopic) redshift estimates, with catalog redshifts ranging from z=0.15 to z>1, with a median z = 0.74. Of the 21 confirmed galaxy clusters, three were previously identified as Abell clusters, three were presented as SPT discoveries in Staniszewski et al, 2009, and three were first identified in a recent analysis of BCS data by Menanteau et al, 2010; the remaining 12 clusters are presented for the first time in this work. Simulated observations of the SPT fields predict the sample to be nearly 100% complete above a mass threshold of M_200 ~ 5x10^14 M_sun/h at z = 0.6. This completeness threshold pushes to lower mass with increasing redshift, dropping to ~4x10^14 M_sun/h at z=1. The size and redshift distribution of this catalog are in good agreement with expectations based on our current understanding of galaxy clusters and cosmology. In combination with other cosmological probes, we use the cluster catalog to improve estimates of cosmological parameters. Assuming a standard spatially flat wCDM cosmological model, the addition of our catalog to the WMAP 7-year analysis yields sigma_8 = 0.81 +- 0.09 and w = -1.07 +- 0.29, a ~50% improvement in precision on both parameters over WMAP7 alone.

• The paper presents a SZ-selected galaxy cluster catalog that improves constraints on cosmological parameters.
• It employs matched filtering and simulations to achieve high detection completeness for massive clusters.
• Optical imaging validates redshift estimates, yielding a 50% improvement in σ₈ and w precision over WMAP7-only results.

Analysis of the SPT-selected Galaxy Clusters via the Sunyaev-Zel'dovich Effect

This paper presents a detection-significance-limited catalog of galaxy clusters selected using the Sunyaev-Zel'dovich (SZ) effect based on observations from the South Pole Telescope (SPT) in 2008. This dataset provides a substantial contribution to cosmology by covering 178 square degrees of the sky, achieving a depth of 18 μK-arcmin at 150 GHz. The catalog comprises 21 confirmed clusters, with their redshifts ranging from 0.15 to over 1 and a median value of 0.74. The paper employs both optical imaging from the Blanco Cosmology Survey (BCS) and Magellan telescopes to validate and estimate the redshifts of these clusters.

Numerical and Methodological Highlights

1. Mass and Redshift Distribution: Simulations predict nearly 100% completeness for clusters above a mass threshold of M_{200} > 5 × 10^{14} M⊙ at z = 0.6. This completeness threshold decreases to approximately 4 × 10^{14} M⊙ at z = 1, showcasing adept calibration of the selection function.
2. Cosmological Parameter Estimation: By incorporating the galaxy cluster catalog within a framework including the WMAP 7-year results, the paper estimates cosmological parameters as follows: σ_8 = 0.81 ± 0.09 and w = -1.07 ± 0.29. This reflects about a 50% improvement in precision for both parameters compared to WMAP7-only results, emphasizing the contribution of SZ-selected clusters to a better understanding of cosmic structure and dynamics.
3. Simulation-based Techniques: The paper uses a simulation pipeline that emulates the effects of atmospheric and instrumental noise and point-source contamination. The SZ selection function accounts for realistic noise conditions and processes the data through matched filtering techniques optimized to identify SZ signatures.

Theoretical and Practical Implications

The data enriches our understanding of cosmological parameters in a wCDM framework. The ability of SZ surveys to span across a wide redshift range without the sensitivity dilution that affects optical and X-ray surveys is highlighted. SZ surveys can provide robust constraints on dark energy models by complementing distance-based tests such as supernovae studies.

However, there are limitations due to uncertainties in the scaling relation between SZ signal and cluster mass, which is affected by intracluster medium physics and the potential for non-thermal pressure support. Moreover, point source contamination remains a concern, necessitating further observational and theoretical refinement.

Future Developments

With forthcoming data from the full SPT survey and collaborative cross-wavelength studies involving X-ray and weak lensing methods, improved precision in scaling relations is expected. These advancements seek to address current uncertainties and contribute to more refined constraints on cosmological parameters, thereby enhancing our understanding of the universe’s dark energy content and the growth of structure.

In summary, the work represents a solid step in the utilization of SZ-selected galaxy clusters for cosmology. The quantitative improvements in parameter estimations provide compelling evidence for the value of SZ surveys in complementing existing cosmological probes. As observational techniques and theoretical models advance, such datasets will undoubtedly bolster our comprehension of cosmic phenomena.