Sunyaev-Zel'dovich Effect Observations of the Bullet Cluster (1e 0657–56) With Apex-Sz

Abstract

We present observations of the Sunyaev-Zel'dovich effect (SZE) in the Bullet cluster (1E 0657-56) using the APEX-SZ instrument at 150 GHz with a resolution of 1 . The main results are maps of the SZE in this massive, merging galaxy cluster. The cluster is detected with 23 σ significance within the central 1 radius of the source position. The SZE map has a broadly similar morphology to that in existing X-ray maps of this system, and we find no evidence for significant contamination of the SZE emission by radio or IR sources. In order to make simple quantitative comparisons with cluster gas models derived from X-ray observations, we fit our data to an isothermal elliptical β model, despite the inadequacy of such a model for this complex merging system. With an X-ray derived prior on the power-law index, β = 1.04 +0.16 −0.10 , we find a core radius r c = 142 ± 18 , an axial ratio of 0.889 ± 0.072, and a central temperature decrement of −771 ± 71 µK CMB , including a ±5.5% flux calibration uncertainty. Combining the APEX-SZ map with a map of projected electron surface density from Chandra X-ray observations, we determine the mass-weighted temperature of the cluster gas to be T mg = 10.8 ± 0.9 keV, significantly lower than some previously reported X-ray spectroscopic temperatures. Under the assumption of an isothermal cluster gas distribution in hydrostatic equilibrium, we compute the gas mass fraction for prolate and oblate spheroidal geometries and find it to be consistent with previous results from X-ray and weak lensing observations. This work is the first result from the APEX-SZ experiment, and represents the first reported scientific result from observations with a large array of multiplexed superconducting transition-edge sensor bolometers.

Untangling the atmosphere of the Bullet cluster with Sunyaev-Zel’dovich effect observations

“…At 150 GHz a CMB brightness decrement has been also found by APEX (Halverson et al 2009) and by the SPT experiment (Plagge et al 2010) with a central value of the SZE consistent with the previous findings.…”

“…i) a radial brightness profile produced by a thermal plasma with the parameters derived by Halverson et al (2009), with an arbitrary normalization; The dot-dashed curve corresponds to the form of the brightness profile produced by a thermal plasma adopting the structure parameters given by Halverson et al (2009), with arbitrary normalization. The dashed curve corresponds to the fit to the data obtained using a model as in Eq.…”

First detection of the Sunyaev Zel'dovich effect increment atλ< 650 μm

“…The center and rightmost panels are respectively the 350 and 500 μm source removed and masked maps; their construction is discussed in the text. The cross hairs show the best fitting SZ effect centroid from Halverson et al (2009); the emission visible at 500 μm but not in the other maps is consistent with the position, shape and flux from the SZ effect expected at this wavelength.…”

Planckintermediate results

“…Early single target SZ studies were limited to the clusters' inner regions (i.e., within R 500 ), and were not really competitive with the X-ray measurements in terms of resolution and sensitivity (see e.g., Pointecouteau et al 2001;Halverson et al 2009;Korngut et al 2011). However, the combination of SZ and X-ray tracers has already shown its potential in terms of structural studies of clusters (Pointecouteau et al 2002;Kitayama et al 2004;Jia et al 2008;Basu et al 2010).…”