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Published April 20, 2012 | Published
Journal Article Open

High Spectral Resolution Measurement of the Sunyaev–Zel'dovich Effect Null with Z-Spec


The Sunyaev-Zel'dovich (SZ) effect spectrum crosses through a null where ΔT_CMB = 0 near ν_0 = 217 GHz. In a cluster of galaxies, ν0 can be shifted from the canonical thermal SZ effect value by corrections to the SZ effect scattering due to the properties of the inter-cluster medium. We have measured the SZ effect in the hot galaxy cluster RX J 1347.5 – 1145 with Z-Spec, an R ~ 300 grating spectrometer sensitive between 185 and 305 GHz. These data comprise a high spectral resolution measurement around the null of the SZ effect and clearly exhibit the transition from negative to positive ΔT_CMB over the Z-Spec band. The SZ null position is measured to be ν_0 = 225.8 ± 2.5(stat.) ± 1.2(sys.) GHz, which differs from the canonical null frequency by 3.0σ and is evidence for modifications to the canonical thermal SZ effect shape. Assuming the measured shift in ν0 is due only to relativistic corrections to the SZ spectrum, we place the limit kT_e = 17.1 ± 5.3 keV from the zero-point measurement alone. By simulating the response of the instrument to the sky, we are able to generate likelihood functions in {y_0, T_e, v_pec} space. For v_pec = 0 km s^(–1), we measure the best-fitting SZ model to be y_0 = 4.6^(+0.6)_(–0.9) × 10^(–4), T_e, 0 = 15.2^(+12)_(–7.4) keV. When v pec is allowed to vary, a most probable value of v_pec = + 450 ± 810 km s^(–1) is found.

Additional Information

© 2012 American Astronomical Society. Received 2011 September 2; accepted 2012 February 3; published 2012 March 29. Our thanks to M. Hollister for his help acquiring the Bolocam data used in this work, J. Filippini for many useful discussions on statistics, and the anonymous referee for useful suggestions which improved this manuscript. The Z-Spec team acknowledges support from the following grants for building and fielding the instrument: NASA SARA grants NAGS-11911 and NAGS-12788, and the NSF AST grant 0807990. Bolocam was constructed and commissioned using funds from NSF/AST-9618798, NSF/AST-0098737, NSF/AST-9980846, NSF/AST-0229008, and NSF/AST-0206158. The Bolocam observation and data analysis efforts were also supported by the Gordon and Betty Moore Foundation. J.S. was partially supported by a NASA Post-doctoral Program fellowship, NSF/AST-0838261, and NASA/NNX11AB07G; N.C. was partially supported by the NASA Graduate Student Research Fellowship. This research has made use of data obtained from the Chandra Data Archive and software provided by the Chandra X-ray Center (CXC) in the application package CIAO.

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