Sunyaev-Zel’dovich observations of galaxy clusters out to the virial radius with the Arcminute Microkelvin Imager★

Abstract

We present observations using the Small Array of the Arcminute Microkelvin Imager (AMI; 14–18 GHz) of four Abell and three MACS clusters spanning 0.171–0.686 in redshift. We detect Sunyaev–Zel’dovich (SZ) signals in five of these without any attempt at source subtraction, although strong source contamination is present. With radio‐source measurements from high‐resolution observations, and under the assumptions of spherical β‐model, isothermality and hydrostatic equilibrium, a Bayesian analysis of the data in the visibility plane detects extended SZ decrements in all seven clusters over and above receiver noise, radio sources and primary cosmic microwave background imprints. Formal Bayesian evidence ratios range from 1011:1 to 1043:1 for six of the clusters and 3000:1 for one with substantially fewer data than the others. We present posterior probability distributions for, e.g., total mass and gas fraction averaged over radii internal to which the mean overdensity is 1000, 500 and 200, r200 being the virial radius. Reaching r200 involves some extrapolation for the nearer clusters but not for the more distant ones. We find that our estimates of gas fraction are low (compared with most in the literature) and decrease with increasing radius. These results appear to be consistent with the notion that gas temperature in fact falls with distance (away from near the cluster centre) out to the virial radius.

The pre-launchPlanckSky Model: a model of sky emission at submillimetre to centimetre wavelengths

“…At present, only limited SZ observations are available. Those observations aim both at studying previously known clusters (Basu et al 2010;Zwart et al 2011;Hincks et al 2010) and at discovering new objects blindly (Vanderlinde et al 2010;Williamson et al 2011;Planck Collaboration 2011c;Marriage et al 2011a;Reichardt et al 2013). They have not only confirmed the existence of the effect but they have also made possible a variety of studies which allow predictions of the general properties of the SZ sky, such as the shape and normalisation of its angular power spectrum (Shaw et al 2009), and the connection between SZ observables and cluster masses or the X-ray luminosity from direct free-free emission of the hot ionised gas Planck Collaboration 2011d,e).…”

Bayesian inference for radio observations

“…Previous Bayesian visibility analyses (Lancaster et al 2005;Zwart et al 2011;AMI Consortium 2012;Sutter et al 2014a) focused on the sky model and were not generalised to include arbitrary instrumental effects (or were attempting to solve for a much more general sky model resulting in many more parameters, thus needing to fix instrumental parameters). The Radio Interferometry Measurement Equation (RIME) (Hamaker, Bregman & Sault 1996;Smirnov 2011a,b) provides a powerful framework to easily describe exactly what happens to a signal as it travels from source to telescope, where it is converted into voltages.…”

Planck2015 results

“…An increasing number of observational studies are measuring the tSZ effect and CIB fluctuations at infrared and submillimetre wavelengths, including investigations of the CIB with the Spitzer Space Telescope (Lagache et al 2007) and the Herschel Space Observatory (Amblard et al 2011;Viero et al 2012Viero et al , 2015, and observations of the tSZ effect with instruments such as the Atacama Pathfinder Experiment (Halverson et al 2009) and Bolocam (Sayers et al 2011). In addition, a new generation of CMB experiments can measure the tSZ effect and CIB at microwave frequencies (Hincks et al 2010;Hall et al 2010;Dunkley et al 2011;Zwart et al 2011;Reichardt et al 2012;Planck Collaboration XXI 2014;Planck Collaboration XXX 2014).…”