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 ∼1043–44 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.