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Published February 1, 2016 | Published + Submitted
Journal Article Open

The discovery of lensed radio and X-ray sources behind the Frontier Fields cluster MACS J0717.5+3745 with the JVLA and Chandra


We report on high-resolution JVLA and Chandra observations of the Hubble Space Telescope (HST) Frontier Cluster MACS J0717.5+3745. MACS J0717.5+3745 offers the largest contiguous magnified area of any known cluster, making it a promising target to search for lensed radio and X-ray sources. With the high-resolution 1.0–6.5 GHz JVLA imaging in A and B configuration, we detect a total of 51 compact radio sources within the area covered by the HST imaging. Within this sample, we find seven lensed sources with amplification factors larger than two. None of these sources are identified as multiply lensed. Based on the radio luminosities, the majority of these sources are likely star-forming galaxies with star-formation rates (SFRs) of 10–50 M_☉ yr^(−1) located at 1 ≾ z ≾ 2. Two of the lensed radio sources are also detected in the Chandra image of the cluster. These two sources are likely active galactic nuclei, given their 2–10 keV X-ray luminosities of ~10^(43–44) erg s^(−1). From the derived radio luminosity function, we find evidence for an increase in the number density of radio sources at 0.6 < z < 2.0, compared to a z < 0.3 sample. Our observations indicate that deep radio imaging of lensing clusters can be used to study star-forming galaxies, with SFRs as low as ~10 M_⊙ yr^(−1), at the peak of cosmic star formation history.

Additional Information

© 2016 The American Astronomical Society. Received 2015 August 25; accepted 2015 December 4; published 2016 January 26. We thank the anonymous referee for useful comments. We thank Megan Gralla for a discussion on the lensed radio sources. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. Support for this work was provided by the National Aeronautics and Space Administration through Chandra Award Number GO4-15129X issued by the Chandra X-ray Observatory Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of the National Aeronautics Space Administration under contract NAS8-03060. R.J.W. is supported by NASA through the Einstein Postdoctoral grant number PF2-130104 awarded by the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory for NASA under contract NAS8- 03060. G.A.O. acknowledges support by NASA through a Hubble Fellowship grant HST-HF2-51345.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. M.B. acknowledges support by the research group FOR 1254 funded by the Deutsche Forschungsgemeinschaft: "Magnetization of interstellar and intergalactic media: the prospects of lowfrequency radio observations." W.R.F., C.J., and F.A.-S. acknowledge support from the Smithsonian Institution. F.A.-S. acknowledges support from Chandra grant GO3-14131X. A.Z. is supported by NASA through Hubble Fellowship grant HST-HF2- 51334.001-A awarded by STScI. This research was performed while T.M. held a National Research Council Research Associateship Award at the Naval Research Laboratory (NRL). Basic research in radio astronomy at NRL by T.M. and T.E.C. is supported by 6.1 Base funding. M.D. acknowledges the support of STScI grant 12065.007-A. P.E.J.N. was partially supported by NASA contract NAS8-03060. E.R. acknowledges a Visiting Scientist Fellowship of the Smithsonian Astrophysical Observatory, and the hospitality of the Center for Astrophysics in Cambridge. Part of this work performed under the auspices of the U.S. DOE by LLNL under Contract DE-AC52-07NA27344. Part of the reported results are based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Data Archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555. This work utilizes gravitational lensing models produced by PIs Bradač Ebeling, Merten & Zitrin, Sharon, and Williams funded as part of the HST Frontier Fields program conducted by STScI. The lens models were obtained from the Mikulski Archive for Space Telescopes (MAST). This research has made use of the NASA/IPAC Infrared Science Archive, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration Facilities: VLA, CXO, HST.

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