Abstract
We have observed regions of three galaxy clusters at z∼[0.06÷0.09] (Abell85, Abell1205, Abell2440) with the Nançay radiotelescope (NRT) to search for 21 cm emission and to fully characterize the FPGA based BAORadio digital backend. We have tested the new BAORadio data acquisition system by observing sources in parallel with the NRT standard correlator (ACRT) back-end over several months. BAORadio enables wide band instantaneous observation of the [1250,1500] MHz frequency range, as well as the use of powerful RFI mitigation methods thanks to its fine time sampling. A number of questions related to instrument stability, data processing and calibration are discussed. We have obtained the radiometer curves over the integration time range [0.01,10 000] seconds and we show that sensitivities of few mJy over most of the wide frequency band can be reached with the NRT. It is clearly shown that in blind line search, which is the context of H I intensity mapping for Baryon Acoustic Oscillations, the new acquisition system and processing pipeline outperforms the standard one. We report a positive detection of 21 cm emission at 3σ-level from galaxies in the outer region of Abell85 at ≃1352 MHz (14400 km/s) corresponding to a line strength of ≃0.8 Jy km/s. We also observe an excess power around ≃1318 MHz (21600 km/s), although at lower statistical significance, compatible with emission from Abell1205 galaxies. Detected radio line emissions have been cross matched with optical catalogs and we have derived hydrogen mass estimates.
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Institut de recherche sur les lois fondamentales de l’Univers.
Laboratoire de l’Accélérateur Linéaire.
The Nançay Radioastronomy Station is part of the Observatoire de Paris and is operated by the Ministère de l’Éducation Nationale and Institut des Sciences de l’Univers of the Centre National de la Recherche Scientifique.
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Acknowledgments
The observations at Nançay would not have been possible with-out the help and support of the operators and of the technical staff of the radio telescope. The Nançay Radio Observatory is the Unité scientifique de Nançay of the Observatoire de Paris, associated as Unité de Service et de Recherche (USR) No. B704 to the French Centre National de la Recherche Scientifique (CNRS). The Nançay Observatory also gratefully acknowledges the financial support of the Conseil régional of the Région Centre in France. We acknowledge financial support from ”Programme National de Cosmologie and Galaxies” (PNCG) of CNRS/INSU, France.
We have made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. Photometric and spectroscopic data from SDSS has also been used. Funding for SDSS-III has been provided by the Alfred P. Sloan Foundation.
We thank Eric Gerard for useful discussions and suggestions. We thank also J. Pezzani and C. Viou, D. Charlet, C. Pailler and M. Taurigna for their help and assistance during observations and understanding the BAORadio system.
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Ansari, R., Campagne, J.E., Colom, P. et al. On sky characterization of the BAORadio wide band digital backend. Exp Astron 41, 117–144 (2016). https://doi.org/10.1007/s10686-015-9477-7
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DOI: https://doi.org/10.1007/s10686-015-9477-7