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The ARCADE2 and LWA1 experiments have claimed an excess over the CosmicMicrowave Background (CMB) at low radio frequencies. If the cosmologicalhigh-redshift contribution to this radio background is between 0.1% and 22% ofthe CMB at 1.42 GHz, it could explain the tentative EDGES Low-Band detection ofthe anomalously deep absorption in the 21-cm signal of neutral hydrogen. We usethe upper limit on the 21-cm signal from the Epoch of Reionization ($z=9.1$)based on 141 hours of observations with LOFAR to evaluate the contribution ofthe high redshift Universe to the detected radio background. Marginalizing overastrophysical properties of star-forming halos, we find (at 95% C.L.) that thecosmological radio background can be at most 9.6% of the CMB at 1.42 GHz. Thislimit rules out strong contribution of the high-redshift Universe to theARCADE2 and LWA1 measurements. Even though LOFAR places limit on the extraradio background, excess of $0.1-9.6$% over the CMB (at 1.42 GHz) is stillallowed and could explain the EDGES Low-Band detection. We also constrain thethermal and ionization state of the gas at $z = 9.1$ and put limits on theproperties of the first star-forming objects. We find that, in agreement withthe limits from EDGES High-Band data, LOFAR data constrain scenarios withinefficient X-ray sources and cases where the Universe was ionized by stars inmassive halos only.

Tight Constraints on the Excess Radio Background at $z = 9.1$ from LOFAR