Jens Erler

The impact of the SZ effect on cm-wavelength (1–30 GHz) observations of galaxy cluster radio relics

Radio relics in galaxy clusters are believed to be associated with powerful shock fronts that originate during cluster mergers, and are a testbed for the acceleration of relativistic particles in the intracluster medium. Recently, radio relic observations have pushed into the cm-wavelength domain (1–30 GHz) where a break from the standard synchrotron power law spectrum has been found, most noticeably in the famous “Sausage” relic. Such spectral steepening is seen as an evidence for non-standard relic models, such as ones requiring seed electron population with a break in their energy spectrum. In this paper, however, we point to an important effect that has been ignored or considered insignificant while interpreting these new high-frequency radio data, namely the contamination due to the Sunyaev-Zel’dovich (SZ) effect that changes the observed synchrotron flux. Even though the radio relics reside in the cluster outskirts, the shock-driven pressure boost increases the SZ signal locally by roughly an order of magnitude. The resulting flux contamination for some well-known relics are non-negligible already at 10 GHz, and at 30 GHz the observed synchrotron fluxes can be diminished by a factor of several from their true values. At higher redshift the contamination gets stronger due to the redshift independence of the SZ effect. Interferometric observations are not immune to this contamination, since the change in the SZ signal occurs roughly at the same length scale as the synchrotron emission, although there the flux loss is less severe than single-dish observations. Besides presenting this warning to observers, we suggest that the negative contribution from the SZ effect can be regarded as one of the best evidence for the physical association between radio relics and shock waves. We present a simple analytical approximation for the synchrotron-to-SZ flux ratio, based on a theoretical radio relic model that connects the nonthermal emission to the thermal gas properties, and show that by measuring this ratio one can potentially estimate the relic magnetic fields or the particle acceleration efficiency.

Planck's view on the spectrum of the Sunyaev–Zeldovich effect

We present a detailed analysis of the stacked frequency spectrum of a large sample of galaxy clusters using Planck data, together with auxiliary data from the AKARI and IRAS missions. Our primary goal is to search for the imprint of relativistic corrections to the thermal Sunyaev-Zeldovich effect (tSZ) spectrum, which allow to measure the temperature of the intracluster medium. We remove Galactic and extragalactic foregrounds with a matched filtering technique, which is validated using simulations with realistic mock data sets. The extracted spectra show the tSZ signal at high significance and reveal an additional far-infrared (FIR) excess, which we attribute to thermal emission from the galaxy clusters themselves. This excess FIR emission from clusters is accounted for in our spectral model. We are able to measure the tSZ relativistic corrections at

The optical design of the six-meter CCAT-prime and Simons Observatory telescopes

2.2\sigma

CCAT-prime: a novel telescope for sub-millimeter astronomy

by constraining the mean temperature of our cluster sample to

Prime-Cam: a first-light instrument for the CCAT-prime telescope

4.4^{+2.1}_{-2.0} \, \mathrm{keV}

CCAT-Prime: science with an ultra-widefield submillimeter observatory on Cerro Chajnantor

. We repeat the same analysis on a subsample containing only the 100 hottest clusters, for which we measure the mean temperature to be

Evidence for a pressure discontinuity at the position of the Coma relic from Planck Sunyaev–Zel'dovich effect data

6.0^{+3.8}_{-2.9} \, \mathrm{keV}

Optical and Sunyaev-Zel'dovich observations of a new sample of distant rich galaxy clusters in the ROSAT All Sky

, corresponding to

ALMA-SZ DETECTION OF A GALAXY CLUSTER MERGER SHOCK AT HALF THE AGE OF THE UNIVERSE

2.0\sigma

Galaxy Cluster Outskirts from the Thermal SZ and Non-Thermal Synchrotron Link

. The temperature of the emitting dust grains in our FIR model is constrained to