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

L. E. Bleem, B. Stalder, T. de Haan, K. A. Aird, S. W. Allen, D. E. Applegate, M. L. N. Ashby, M. Bautz, M. Bayliss, B. A. Benson, S. Bocquet, M. Brodwin, J. E. Carlstrom, C. L. Chang, I. Chiu, H. M. Cho, A. Clocchiatti, T. M. Crawford, A. T. Crites, S. Desai, J. P. Dietrich, M. A. Dobbs, R. J. Foley, W. R. Forman, E. M. George, M. D. Gladders, A. H. Gonzalez, N. W. Halverson, C. Hennig, H. Hoekstra, G. P. Holder, W. L. Holzapfel, J. D. Hrubes, C. Jones, R. Keisler, L. Knox, A. T. Lee, E. M. Leitch, J. Liu, M. Lueker, D. Luong-Van, A. Mantz, D. P. Marrone, M. McDonald, J. J. McMahon, S. S. Meyer, L. Mocanu, J. J. Mohr, S. S. Murray, S. Padin, C. Pryke, C. L. Reichardt, A. Rest, J. Ruel, J. E. Ruhl, B. R. Saliwanchik, A. Saro, J. T. Sayre, K. K. Schaffer, T. Schrabback, E. Shirokoff, J. Song, H. G. Spieler, S. A. Stanford, Z. Staniszewski, A. A. Stark, K. T. Story, C. W. Stubbs, K. Vanderlinde, J. D. Vieira, A. Vikhlinin, R. Williamson, O. Zahn, A. Zenteno

TL;DR

This work delivers a complete SZ-selected galaxy cluster catalog from the 2500 deg^2 SPT-SZ survey, comprising 677 candidates with 516 confirmed clusters and 251 new discoveries. Through optical/NIR follow-up and spectroscopy, the authors provide redshifts and mass estimates, revealing a nearly redshift-independent mass threshold and a median redshift of 0.55 for a massive, high-purity sample extending to z>1.4. The catalog, complemented by X-ray, lensing, and multi-wavelength data, offers a powerful dataset for cosmology and studies of cluster formation and evolution, with future work to refine mass calibration and cosmological constraints. The study demonstrates the effectiveness of high-resolution SZ surveys in producing large, clean, and cosmologically valuable cluster samples across a broad redshift range.

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 $ξ$ =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 $ξ$>4.5 candidates and 387 (or 95%) of the $ξ$>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 $M_{\scriptsize 500c}(ρ_\mathrm{crit})$ ~ 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.

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

TL;DR

This work delivers a complete SZ-selected galaxy cluster catalog from the 2500 deg^2 SPT-SZ survey, comprising 677 candidates with 516 confirmed clusters and 251 new discoveries. Through optical/NIR follow-up and spectroscopy, the authors provide redshifts and mass estimates, revealing a nearly redshift-independent mass threshold and a median redshift of 0.55 for a massive, high-purity sample extending to z>1.4. The catalog, complemented by X-ray, lensing, and multi-wavelength data, offers a powerful dataset for cosmology and studies of cluster formation and evolution, with future work to refine mass calibration and cosmological constraints. The study demonstrates the effectiveness of high-resolution SZ surveys in producing large, clean, and cosmologically valuable cluster samples across a broad redshift range.

Abstract

We present a catalog of galaxy clusters selected via their Sunyaev-Zel'dovich (SZ) effect signature from 2500 deg 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 =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 >4.5 candidates and 387 (or 95%) of the >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 ~0.25 leading to a sample of massive clusters that extends to high redshift. The median mass of the sample is ~ 3.5 x 10, the median redshift is =0.55, and the highest-redshift systems are at >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.

Paper Structure

This paper contains 31 sections, 13 equations, 8 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Observations and Data Reduction
  3. Telescope and Observations
  4. Map Making
  5. Cluster Extraction and mm-wave Characterization
  6. Cluster Extraction
  7. Integrated Comptonization
  8. Contamination
  9. Follow-up Observations
  10. Follow-up Strategy
  11. Targeted Observations and Data Reduction
  12. Optical Data
  13. Near-Infrared Data
  14. Spectroscopic Observations
  15. Other Datasets
  16. ...and 16 more sections

Figures (8)

  • Figure 1: Visual representation of the SPT-SZ data and matched filtering process described in §\ref{['sec:obs']} and §\ref{['sec:extract']}. Panels (a) and (b) show $6^\circ$-by-$6^\circ$ cutouts of 95 and 150 GHz maps from the ra21hdec$-$60 field; the displayed temperature range is $\pm 300 \mu K$. These maps are made from data that have been only minimally filtered (scan-direction high-pass filter at $l$$\sim$50) and show the main features of SPT-SZ survey data: large-scale primary CMB fluctuations, emissive point sources, and SZ decrements from galaxy clusters. Panel (c) shows the azimuthally averaged spatial-spectral filter optimized for detection of $\theta_{c} =0\hbox{$.\mkern-4mu^\prime$}25$ clusters, with the red-dashed (blue-solid) curves showing the Fourier-domain coefficients for the 95 (150) GHz data. Panel (d) shows a zoomed-in view of the $1^\circ$-by-$1^\circ$ area delineated by the dashed box in panel (b) after the spatial-spectral filter has been applied. This map is in units of signal-to-noise, and the displayed range is $-5 < S/N < 5$. Visible in this panel are the $\xi=22.2$, $z=1.132$ cluster SPT-CL J2106$-$5844 and the $\xi=4.6$, optically unconfirmed candidate SPT-CL J2106$-$5820.
  • Figure 2: Simulated false-detection rate for each of the 19 fields in the SPT-SZ survey. Plotted is the cumulative density of false detections above a detection significance, $\xi_\textrm{min}$. We expect 18.5 false detections at $\xi \ge 5$ and 172 at $\xi \ge 4.5$ for the entire survey.
  • Figure 3: Results of red-sequence model calibration. (Top) Photometric redshift, $z_\mathrm{est}$, versus spectroscopic redshift, $z_\mathrm{spec}$, for 129 spectroscopically confirmed SPT clusters. We plot the aggregate model tunings for Swope/SITe3, MPG/ESO WFI, the larger class telescopes (for which the model was calibrated across instruments as all clusters were observed in the griz system), and Spitzer/IRAC. Some clusters are plotted multiple times (at most once per model) as they were observed with multiple telescopes to calibrate the various redshift models. (Bottom) Distribution of redshift residuals $\Delta z / \sigma_{z} = (z_\mathrm{spec} - z_\mathrm{est})/\sigma_{z_\mathrm{est}}$. The typical redshift uncertainty, $\sigma_{z}$, scales as $\sim0.013- 0.018(1+z)$ for redshifts estimated using combinations of griz filters, $\sim0.021(1+z)$ for clusters imaged with the MPG/ESO WFI, $\sim0.025(1+z)$ for Swope/SITe3, and as $\sim0.035 (1+z)$ for redshifts determined using Spitzer /IRAC.
  • Figure 4: (Left) SPT-CL J0459$-$4947, one of three SPT clusters with an estimated redshift of $z > 1.5$ (rgb: Spitzer/IRAC 4.5, 3.6 $\mu m$, Magellan/IMACS z-band; over-plotted are the contours of the SZ detection). (Right) Spitzer color-magnitude diagram (with magnitudes relative to Vega): plotted in gray are all galaxies in the Spitzer field, over-plotted in red are the galaxies identified with the SZ detection. The galaxies of this massive system ($M_{500c}\sim 3 \times 10^{14} M_\odot h_{70}^{-1}$) have significantly redder Spitzer colors than spectroscopically confirmed SPT-CL J2040$-$4451 at $z=1.478$ (blue), supporting that its redshift is greater than $z=1.5$. The color-magnitude relations of the best-fit model redshifts are over-plotted as dashed lines and the locations of model L$^{*}$ galaxies are indicated via "$\ast$". The best-fit redshift is $z=1.7 \pm 0.2$, but the model is poorly calibrated at such high redshifts.
  • Figure 5: (Left) Plot of maximum detection significance, $\xi$, versus redshift for the confirmed SPT-SZ cluster sample; black points correspond to systems with photometrically estimated redshifts while red points represent spectroscopically confirmed clusters. We report lower limits for the redshifts of the three highest-redshift systems (see §\ref{['sec:nirredshift']}). (Right) The redshift distribution of the confirmed cluster sample; the median redshift of the sample is $z=0.55$. The histogram does not have integer values as clusters with photometric redshift uncertainties were distributed amongst the appropriate bins.
  • ...and 3 more figures