First detection of the Sunyaev Zel'dovich effect increment at lambda < 650 um

TL;DR

This paper reports the first detection of the Sunyaev-Zel'dovich effect increment at wavelengths shorter than 650 micrometers using Herschel SPIRE observations of the Bullet cluster, confirming the spectral distortion at these submillimeter wavelengths.

Contribution

It presents the first measurement of the SZ effect increment at lambda < 650 um, demonstrating SPIRE's capability to detect relativistic SZ effects in galaxy clusters.

Findings

Detected SZ effect at 350 and 500 um wavelengths.

Measured central intensities consistent with previous 2 mm observations.

Indicated the significance of finite temperature SZ correction at 2.1 sigma.

Abstract

The Sunyaev-Zel'dovich (SZ) effect is a spectral distortion of the cosmic microwave background as observed through the hot plasma in galaxy clusters. This distortion is a decrement in the CMB intensity for lambda > 1.3 mm, an increment at shorter wavelengths, and small again by lambda ~250 um. As part of the Herschel Lensing Survey (HLS) we have mapped 1E0657-56 (the Bullet cluster) with SPIRE with bands centered at 250, 350 and 500 um and have detected the SZ effect at the two longest wavelengths. The measured SZ effect increment central intensities are Delta I_{0} = 0.097 +- 0.019 MJy sr^{-1} at 350 um and Delta I_{0} = 0.268 +- 0.031 MJy sr^{-1} at 500 um, consistent with the SZ effect spectrum derived from previous measurements at 2 mm. No other diffuse emission is detected. The presence of the finite temperature SZ effect correction is preferred by the SPIRE data at a significance of 2.1 sigma, opening the possibility that the relativistic SZ effect correction can be constrained by SPIRE in a sample of clusters. The results presented here have important ramifications for both sub-mm measurements of galaxy clusters and blank field surveys with SPIRE.