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Published December 10, 2012 | Published
Journal Article Open

A Multi-wavelength Study of the Sunyaev-Zel'dovich Effect in the Triple-merger Cluster MACS J0717.5+3745 with MUSTANG and Bolocam


We present 90, 140, and 268 GHz subarcminute resolution imaging of the Sunyaev-Zel'dovich effect (SZE) in the disturbed, intermediate-redshift (z = 0.5458) galaxy cluster MACS J0717.5+3745, a triple-merger system comprising four distinct, optically detected subclusters. Our 90 GHz SZE data result in a sensitive, 34 μJy beam^(–1) map of the SZE at 13" effective resolution using the MUSTANG bolometer array on the Green Bank Telescope (GBT). Our 140 and 268 GHz SZE imaging, with resolutions of 58" and 31" and sensitivities of 1.8 and 3.3 mJy beam^(–1), respectively, was obtained through observations from the Caltech Submillimeter Observatory using Bolocam. We compare these maps to a two-dimensional pressure map derived from Chandra X-ray observations. Our MUSTANG SZE data confirm previous indications from Chandra of a pressure enhancement due to shock-heated, ≳ 20 keV gas immediately adjacent to extended radio emission seen in low-frequency radio maps of this cluster. MUSTANG also detects pressure substructure that is not well constrained by the Chandra X-ray data in the remnant core of a merging subcluster. We find that the small-scale pressure enhancements in the MUSTANG data amount to ~2% of the total pressure measured in the 140 GHz Bolocam observations. The X-ray inferred pseudo-pressure template also fails on larger scales to accurately describe the Bolocam data, particularly at the location of the subcluster with a remnant core known to have a high line-of-sight optical velocity of ~3200 km s^(–1). Our Bolocam data are adequately described when we add an additional component—not described by a thermal SZE spectrum—to the X-ray template coincident with this subcluster. Using flux densities extracted from our model fits, and marginalizing over the X-ray spectroscopic temperature constraints for the region, we fit a thermal + kinetic SZE spectrum to our Bolocam data and find that the subcluster has a best-fit line-of-sight proper velocity vz = 3600^(+3440)_(–2160) km s^(–1), in agreement with the optical velocity estimates for the subcluster. The probability v_z ≤ 0 given our measurements is 2.1%. Repeating this analysis using flux densities measured directly from our maps results in a 3.4% probability v_z ≤ 0. We note that this tantalizing result for the kinetic SZE is on resolved, subcluster scales.

Additional Information

© 2012 American Astronomical Society. Received 2012 April 27; accepted 2012 October 23; published 2012 November 20. We thank Maxim Markevitch, Simona Giacintucci, Cheng-Jiun Ma, and Dan Coe for useful discussions and input. We also thank Reinout van Weeren, Adi Zitrin, Annalisa Bonafede, and Marceau Limousin for providing radio and lensing maps and for their input, which aided tremendously in the interpretation of the cluster astrophysics. We thank Marie Rex, Eiichi Egami, and Tim Rawle for their support in obtaining the 268 GHz Bolocam observations. The late-night assistance of the GBT operators was much appreciated during the observations, as was the overall support from all those at the GBT. We also thank Ashley Reichardt for her help in performing the MUSTANG observations. We are grateful for CSO administrative support from Kathy Deniston, Barbara Wertz, and Diana Bisel, and for Bolocam instrument maintenance and support from the CSO day crew. We also thank the many folks who helped in obtaining the CARMA/SZA observations presented here, particularly Tom Culverhouse, Nikolaus Volgenau, John Carpenter, and the many students and postdocs who regularly help run the array. We are especially grateful to Stephen Muchovej and Erik Leitch for their work on the pipeline that allows data from the CARMA/SZA subarray to be easily calibrated against Mars. Much of the work presented here was supported by National Science Foundation (NSF) grant AST-1007905. Support for T.M. was provided by NASA through the Einstein Fellowship Program, grant PF0-110077. Support for A.Y. was provided by the National Radio Astronomy Observatory (NRAO) graduate student support program. Support for P.K. was provided by the NASA Postdoctoral Program (NPP). J.S. was supported by NSF/AST-0838261 and NASA/NNX11AB07G. N.C. was partially supported by a NASA Graduate Student Research Fellowship. K.U. acknowledges support from the Academia Sinica Career Development Award and the National Science Council of Taiwan under grant NSC100-2112-M-001-008-MY3. The NRAO is a facility of the NSF operated under cooperative agreement by Associated Universities, Inc. The MUSTANG observations presented here were obtained with time on the GBT allocated under NRAO proposal IDs AGBT10A056 and AGBT11B001. The Bolocam data were acquired through observations at the CSO, which is operated by the California Institute of Technology under cooperative agreement with the NSF (AST-0838261). A portion of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. We also thank Nina the dog for always standing by patiently and never questioning the value of this work.

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