[Paper Review] The ATLAS-SPT Radio Survey of Cluster Galaxies

Andrew O’Brien, N. F. H. Tothill+2 more|arXiv (Cornell University)|Feb 5, 2016

Galaxies: Formation, Evolution, Phenomena2 references4 citations

TL;DR

This paper presents the ATLAS-SPT radio survey, a 100 deg² mosaic of the SPT deep field at 2.1 GHz using the ATCA, achieving 8" resolution and 80 μJy rms sensitivity. It identifies 75 bent-tail radio galaxy candidates as tracers of galaxy clusters and finds no significant spatial correlation with SPT-SZ-selected clusters, suggesting these radio-selected clusters trace a distinct population, potentially revealing high-redshift clusters missed by SZ surveys.

ABSTRACT

Using a high-performance computing cluster to mosaic 4,787 pointings, we have imaged the 100 sq. deg. South Pole Telescope (SPT) deep-field at 2.1 GHz using the Australian Telescope Compact Array to an rms of 80 $μ$Jy and a resolution of 8". Our goal is to generate an independent sample of radio-selected galaxy clusters to study how the radio properties compare with cluster properties at other wavelengths, over a wide range of redshifts in order to construct a timeline of their evolution out to $z \sim 1.3$. A preliminary analysis of the source catalogue suggests there is no spatial correlation between the clusters identified in the SPT-SZ catalogue and our wide-angle tail galaxies.

Motivation & Objective

• To conduct a wide-area, high-sensitivity radio survey of the SPT deep field to identify galaxy clusters via bent-tail radio galaxies.
• To compare radio-selected cluster candidates with those detected via the Sunyaev-Zel’dovich (SZ) effect to assess selection biases.
• To investigate the evolution of radio properties in galaxy clusters out to redshift z ~ 1.3.
• To explore the potential of bent-tail radio galaxies as a complementary method for detecting high-redshift clusters.
• To fill the centimetre-wavelength radio coverage gap in the multi-wavelength SSDF field.

Proposed method

• Mosaicked 4,787 pointings across 100 deg² using the ATCA in 6A and 6C configurations to achieve 8" resolution and 80 μJy rms sensitivity.
• Used Nyquist sampling with hexagonal grid spacing based on the 3.1 GHz primary beam FWHM to ensure complete coverage and avoid undersampling.
• Applied standard calibration using PKS 1934-638 (flux) and PKS 2333-528 (phase) calibrators, with automated RFI flagging via pgflag.
• Performed wideband imaging and source detection using the MIRIAD software package, focusing on Stokes I total intensity.
• Identified bent-tail radio galaxy candidates manually due to complex morphology and low sky density.
• Cross-matched bent-tail candidates with the SPT-SZ cluster catalogue to assess spatial correlation at cluster redshifts.

Experimental results

Research questions

• RQ1 Do bent-tail radio galaxies detected in the ATLAS-SPT survey trace the same population of galaxy clusters as those detected via the SZ effect?
• RQ2 What is the spatial correlation between radio-selected bent-tail galaxies and SZ-selected clusters in the SPT deep field?
• RQ3 To what extent do SZ surveys miss high-redshift clusters that are detectable via bent-tail radio galaxies?
• RQ4 How effective is the bent-tail radio galaxy method for identifying massive, high-redshift galaxy clusters?
• RQ5 What are the selection biases in SZ cluster surveys related to the presence of bright radio AGN?

Key findings

• The ATLAS-SPT survey achieved a 2.1 GHz image of 100 deg² with 8" resolution and 80 μJy rms sensitivity, covering the full SSDF field.
• A total of 75 bent-tail radio galaxy candidates were detected, with two shown in Figure 3 as representative examples.
• Only one bent-tail candidate lies within 2 Mpc of its nearest SPT-SZ cluster, and four are within 4 Mpc, indicating minimal spatial correlation.
• The lack of significant spatial correlation suggests that bent-tail radio galaxies trace a different population of galaxy clusters than those detected by the SPT-SZ survey.
• The survey extends radio source detection to z ~ 1.3 with a 5σ flux limit of 0.4 mJy, enabling the study of high-redshift cluster evolution.
• The method of using bent-tail galaxies may reveal high-redshift clusters that are missed by SZ surveys due to AGN contamination or low mass.