  21-cm cosmology provides an exciting opportunity to probe new physics
dynamics in the early universe. In particular, a tiny sub-component of dark
matter that interacts strongly with the visible sector may cool the gas in the
intergalactic medium and significantly alter the expected absorption signal at
Cosmic Dawn. However, the information about new physics in this observable is
obscured by astrophysical systematic uncertainties. In the absence of a
microscopic framework describing the astrophysical sources, these uncertainties
can be encoded in a bottom up effective theory for the 21-cm observables in
terms of unconstrained astrophysical fluxes. In this paper, we take a first
step towards a careful assessment of the degeneracies between new physics
effects and the uncertainties in these fluxes. We show that the latter can be
constrained by combining measurements of the UV luminosity function, the Planck
measurement of the CMB optical depth to reionization, and an upper bound on the
unresolved X-ray flux. Leveraging those constraints, we demonstrate how new
physics signatures can be disentangled from astrophysical effects. Focusing on
the case of millicharged dark matter, we find sharp predictions, with small
uncertainties within the viable parameter space.
