Galaxy Clusters Discovered via the Sunyaev-Zel'dovich Effect in the 2500-square-degree SPT-SZ survey (1409.0850v2)

Abstract: We present a catalog of galaxy clusters selected via their Sunyaev-Zel'dovich (SZ) effect signature from 2500 deg$^2$ of South Pole Telescope (SPT) data. This work represents the complete sample of clusters detected at high significance in the 2500-square-degree SPT-SZ survey, which was completed in 2011. A total of 677 (409) cluster candidates are identified above a signal-to-noise threshold of $\xi$ =4.5 (5.0). Ground- and space-based optical and near-infrared (NIR) imaging confirms overdensities of similarly colored galaxies in the direction of 516 (or 76%) of the $\xi$>4.5 candidates and 387 (or 95%) of the $\xi$>5 candidates; the measured purity is consistent with expectations from simulations. Of these confirmed clusters, 415 were first identified in SPT data, including 251 new discoveries reported in this work. We estimate photometric redshifts for all candidates with identified optical and/or NIR counterparts; we additionally report redshifts derived from spectroscopic observations for 141 of these systems. The mass threshold of the catalog is roughly independent of redshift above $z$~0.25 leading to a sample of massive clusters that extends to high redshift. The median mass of the sample is $M_{\scriptsize 500c}(\rho_\mathrm{crit})$ ~ 3.5 x 10$^{14} M_\odot h^{-1}$, the median redshift is $z_{med}$ =0.55, and the highest-redshift systems are at $z$>1.4. The combination of large redshift extent, clean selection, and high typical mass makes this cluster sample of particular interest for cosmological analyses and studies of cluster formation and evolution.

• The paper introduces a catalog of 677 galaxy clusters detected via the SZ effect, with 516 optically confirmed and 251 identified for the first time.
• The study employs a multi-wavelength method combining SZ, optical, and NIR data to determine photometric and spectroscopic redshifts with a median of 0.55.
• The analysis reveals significant cluster masses, including SPT-CL J2106-5844 at 8.35×10^14 M☉, underscoring the survey's value for cosmological research.

An Overview of the Galaxy Cluster Catalog from the SPT-SZ Survey

The research paper under consideration presents an extensive galaxy cluster catalog derived from the Sunyaev-Zel’dovich (SZ) effect signatures captured in the South Pole Telescope SZ (SPT-SZ) survey, which covers an expansive 2500 square degrees of the southern sky. The catalog is the outcome of a multi-faceted observational campaign aimed at leveraging the unique properties of the SZ effect for cluster detection, offering a nearly redshift-independent method for identifying clusters, which presents advantages over traditional X-ray or optical detection techniques.

Key Findings and Methodology

The SPT-SZ survey's catalog comprises 677 cluster candidates identified with a signal-to-noise threshold of 4.5σ, with 516 of these candidates confirmed via optical and near-infrared (NIR) imaging. This robustness in detection is confirmed by simulations predicting a high level of sample purity, further corroborated by optical/NIR follow-up confirmations. Of particular note, 251 cluster discoveries are reported for the first time, highlighting the utility of the SZ effect in detecting previously unknown clusters.

The paper reports the photometric redshifts for the confirmed clusters and spectroscopic redshifts for 141 systems. The photometric redshift determination relies on red-sequence methods and NIR data, offering valuable redshift estimates even in challenging observational scenarios. The median redshift of the clusters is 0.55, with a mass threshold approximately constant above a redshift of 0.25.

The Characteristics and Implications of the Cluster Sample

The catalog represents a substantial assembly of massive galaxy clusters extending to high redshifts, with clusters discovered up to redshifts greater than 1.4. The sample's median mass is reported at M500c≈3.5×10^14 h⁻¹_70 M☉, establishing it as a significant dataset for studies of cosmological structures and the growth of the universe. This mass and redshift distribution appear nearly constant with regard to redshift, a testament to the effectiveness of the SZ selection technique that mitigates biases tied to traditional methods influenced by redshift-related dimming and dilution effects.

Strong Numerical Results and Notable Observations

Among the substantive numerical highlights is the detection of SPT-CL J2106-5844, the most massive known cluster above redshift 1, with M500c=8.35×10^14 h⁻¹_70 M☉. Additionally, the paper identifies several clusters as strong gravitational lenses, offering significant opportunities for further astrophysical exploration. The strongest detection in the sample, SPT-CL J2248-4431 (Abell S1063), underscores the catalog's importance for both observational astronomers and cosmologists seeking to refine our understanding of dark matter and energy.

Implications for Future Research

This work presents robust implications for cosmological studies. The homogeneity of the detected cluster sample across redshifts makes it an exemplary dataset for examining the dynamics of large structures and the properties of the early universe. Moreover, the mass-redshift relation reported here sets foundational data for future studies that aim to incorporate additional observational data from radio, X-ray, and other wavelengths.

Future developments may include expanded observations and refined analysis techniques, potentially improving the precision of mass estimates and further reducing uncertainties related to SZ-mass relations. The SPT-3G and similar surveys poised to utilize next-generation detectors could vastly increase the scope and resolution of such surveys, solidifying the role of SZ-based cluster detection in frontline astrophysics.

Conclusion

The SPT-SZ survey catalog establishes a significant benchmark in the paper of galaxy clusters. By leveraging the SZ effect, this research not only expands our current catalog of clusters but also enhances our tools for probing the cosmos at unprecedented scales. The implications of this paper extend into varied domains of astrophysics, promising a foundation upon which future theoretical and observational work will build.