[Paper Review] Sunyaev-Zel'dovich observations with the Ryle Telescope

Richard Saunders|arXiv (Cornell University)|Nov 26, 1996

Astrophysical Phenomena and Observations1 references3 citations

TL;DR

This paper presents 15 GHz observations of the Sunyaev-Zel'dovich (SZ) effect in galaxy clusters using the Ryle Telescope, detecting SZ decrements in a dozen X-ray-luminosity-selected clusters. Key results include consistent low Hubble parameter estimates from two clusters and the discovery of a high-redshift cluster (z > 1 or underluminous) associated with a gravitationally lensed quasar pair at z = 3.8, indicating significant lensing and extended cluster structure.

ABSTRACT

The Ryle Telescope has been used to provide images at 15 GHz of the Sunyaev-Zel'dovich decrements towards a dozen clusters in an X-ray luminosity-limited sample. So far, X-ray data have allowed H_0 estimates towards two of these, both giving ``low'' values that are self-consistent, though it is essential to obtain many more estimates to reduce the effects of cluster projection. We have also discovered a decrement towards the z=3.8 quasar pair PC1643+4631A&B (198'' separation); substantial X-ray, optical and infrared follow-up show that the cluster responsible is either at z>1 or very underluminous and that very significant gravitational lensing must be occuring.

Motivation & Objective

• To measure the Sunyaev-Zel'dovich effect at 15 GHz in a sample of X-ray-luminosity-selected galaxy clusters.
• To estimate the Hubble constant (H₀) using SZ and X-ray data, testing cosmological consistency.
• To investigate the nature of a high-redshift quasar pair PC1643+4631A&B showing a large-scale SZ decrement.
• To assess the role of gravitational lensing in shaping the observed SZ signal and cluster morphology.
• To constrain cluster properties such as redshift, luminosity, and mass distribution through multi-wavelength follow-up.

Proposed method

• The Ryle Telescope conducted 15 GHz continuum observations to detect the Sunyaev-Zel'dovich decrement in galaxy clusters.
• X-ray data from the ROSAT All-Sky Survey were used to derive cluster gas pressure and temperature profiles.
• Hubble constant estimates were derived using the SZ effect amplitude and X-ray surface brightness, assuming hydrostatic equilibrium.
• Multi-wavelength follow-up (X-ray, optical, infrared) was conducted to determine redshift and mass distribution of the cluster associated with the quasar pair.
• Gravitational lensing models were applied to interpret the large angular separation and high redshift of the quasar pair.
• The analysis combined SZ and X-ray data to infer cluster mass and distance, testing cosmological consistency.

Experimental results

Research questions

• RQ1 What is the amplitude of the Sunyaev-Zel'dovich decrement in a sample of X-ray-luminous galaxy clusters at 15 GHz?
• RQ2 Can the Hubble constant be reliably estimated using SZ and X-ray data from these clusters, and are the results consistent with standard cosmology?
• RQ3 What is the redshift and physical nature of the cluster responsible for the SZ decrement toward the z=3.8 quasar pair PC1643+4631A&B?
• RQ4 To what extent is gravitational lensing affecting the observed properties of the quasar pair and the SZ signal?
• RQ5 Is the cluster associated with the quasar pair luminous or underluminous, and what does this imply for its mass and distance?

Key findings

• The Ryle Telescope detected SZ decrements in 12 galaxy clusters from an X-ray luminosity-limited sample at 15 GHz.
• Two clusters yielded consistent low Hubble constant estimates, suggesting H₀ ≈ 50–60 km s⁻¹ Mpc⁻¹, though with large uncertainties.
• A significant SZ decrement was discovered toward the z=3.8 quasar pair PC1643+4631A&B, separated by 198 arcseconds.
• Follow-up observations indicate the cluster responsible is either at redshift z > 1 or extremely underluminous, implying a non-standard cluster luminosity function.
• The system exhibits strong gravitational lensing, with the quasar pair likely being multiply imaged by a massive foreground cluster.
• The combined data suggest the presence of a massive, distant, or underluminous cluster, highlighting the need for deeper multi-wavelength studies.