Searching for Kardashev Type III civilisations from High $q$-Value
  Sources in the LoTSS-DR1 Value-added Catalogue
  Kardashev Type III civilisations have by definition energy requirements that
are likely to generate strong excess emission in the mid-infrared (MIR) that is
associated with the waste heat they generate. For those civilisations that
capture starlight via Dyson sphere like constructions, the Optical to MIR flux
ratio of the host galaxies is also expected to be unusually low. Since a wide
range of galaxy types adhere to the infrared-radio correlation (IRC), galaxies
hosting Type III civilisations should also strongly deviate from this relation.
Radio data can therefore play a crucial role in breaking the degeneracy between
the effects of dust obscuration in a galaxy and the signature of an
energy-intensive civilisation. We have used the newly released LoTSS-DR1
value-added catalogue to create a sample of 16,367 $z < 0.2$ sources with radio
and MIR flux densities, optical photometry and (photometric) redshifts. We
calculated the IRC parameter $q^{{\rm22~\mu m}}_{{\rm 150~MHz}}$ =
log($S_{150~{\rm MHz}}$/$S_{22~{\rm \mu m}}$) and identified 21 sources with
exceptionally high values of $q^{{\rm22~\mu m}}_{{\rm 150~MHz}}$, an indication
of MIR emission enhanced by a factor of $\sim$ 10. Out of the 21 high $q$-value
sources, 4 sources have very red MIR colors, and appear to have relatively low
optical/MIR ratios. Two of the 4 sources are not well known in the literature,
they are considered as potential hosts of Type III civilisations. These sources
deserve further study and investigation. Finally, we note that extending our
analysis to the full LoTSS survey area can place very strong constraints on the
incidence of Type III civilisations in the universe.
