Low-resolution spectroscopy of the Sunyaev-Zel’dovich effect and estimates of cluster parameters

Abstract

Context. The Sunyaev-Zel'dovich (SZ) effect is a powerful tool for studying clusters of galaxies and cosmology. Large mm-wave telescopes are now routinely detecting and mapping the SZ effect in a number of clusters, measure their comptonisation parameter and use them as probes of the large-scale structure and evolution of the universe. Aims. We show that estimates of the physical parameters of clusters (optical depth, plasma temperature, peculiar velocity, non-thermal components etc.) obtained from ground-based multi-band SZ photometry can be significantly biased, owing to the reduced frequency coverage, to the degeneracy between the parameters and to the presence of a number of independent components larger than the number of frequencies measured. We demonstrate that low-resolution spectroscopic measurements of the SZ effect that also cover frequencies >270 GHz are effective in removing the degeneracy. Methods. We used accurate simulations of observations with lines-of-sight through clusters of galaxies with different experimental configurations (4-band photometers, 6-band photometer, multi-range differential spectrometer, full coverage spectrometers) and different intracluster plasma stratifications. Results. We find that measurements carried out with ground-based few-band photometers are biased towards high electron temperatures and low optical depths, and require coverage of high frequency and/or independent complementary observations to produce unbiased information; a differential spectrometer that covers 4 bands with a resolution of ∼6 GHz eliminates most if not all bias; full-range differential spectrometers are the ultimate resource that allows a full recovery of all parameters.

On the emissivity of wire-grid polarizers for astronomical observations at mm-wavelengths

“…8 we plot a simulation of a 3-hours observation of the Sunyaev-Zeldovich (SZ) effect in a typical cluster of galaxies, obtained using a room-temperature differ- ential MPI on a stratospheric balloon (like the OLIMPO experiment [15]), with photon-noise limited TES detectors working in bands optimized as described above. See [16] for details. The potential of this method is evident, despite of the bandwidth limitation due to the emissivity of the WGs discussed here.…”

Galaxy clusters as probes for cosmology and dark matter

“…requires detailed spectral informations in the whole mm range. de Bernardis et al 26 have shown that a differential spectrometer covering four bands with a resolution of ∼ 6 GHz eliminates most of the bias resolution in a full recovery of the input cluster parameters. This possibility is clearly hampered in ground-based few-band photometers while spectrometers suitable for balloon borne observations or for dedicated space missions would make the necessary step forward.…”

“…OLIMPO will be launched on June 2017 from Svalbard Islands and will represent the first possibility to explore the use of a FTS coupled with a four-band photometer in the millimetric and sub-millimetric range. Simulations 26 show that even a warm spectrometer, mounted on a balloon borne experiment like OLIMPO, 72 allows an unbiased recovery of the galaxy cluster thermal optical depth, electron temperature, dust contamination, non-thermal optical depth, despite being still limited at high frequencies by radiative background. A low earth-orbit satellite like SAGACE 27 improves the capability to detect non-thermal effects and the disentangling from foregrounds.…”

Precision CMB measurements with long-duration stratospheric balloons: activities in the Arctic

“…The DFTS is intrinsically rejecting the large common mode signal from the telescope, the residual atmosphere and the CMB monopole. The effectiveness of this instrument in removing degeneracies between cluster (and foreground) parameters has been discussed in de Bernardis et al 2012. OLIMPO will carry-out an ambitious observation program, including spectroscopic observations of the SZ in 40 known clusters, plus a 10 • × 10 • blind deep-sky survey.…”