The contribution of discrete sources to the sky temperature at 144 MHz
  In recent years, the level of the extragalactic radio background has become a
point of considerable interest, with some lines of argument pointing to an
entirely new cosmological synchrotron background. The contribution of the known
discrete source population to the sky temperature is key to this discussion.
Because of the steep spectral index of the excess over the cosmic microwave
background, it is best studied at low frequencies where the signal is
strongest. The Low-Frequency Array (LOFAR) wide and deep sky surveys give us
the best constraints yet on the contribution of discrete extragalactic sources
at 144 MHz, and in particular allow us to include contributions from diffuse,
low-surface-brightness emission that could not be fully accounted for in
previous work. We show that, even with these new data, known sources can still
only account for around a quarter of the estimated extragalactic sky
temperature at LOFAR frequencies.
