  Optical/near-IR broadband photometry of the halos of blue compact galaxies
(BCGs) have revealed a very red spectral energy distribution, which cannot
easily be reconciled with any normal, metal-poor stellar population. Here,
three possible explanations for the red excess are explored: nebular emission,
metal-rich stars and a stellar population with a very bottom-heavy initial mass
function (IMF). We find, that nebular emission in BCG halos would produce very
blue near-IR colours, and hence fails to explain the observed red excess.
Although metal-rich stars may in principle explain the colours observed, the
required stellar metallicity is very high (solar or higher), which would be a
curious halo property given the low gas metallicity (~10% solar) of the central
starburst in these objects. A stellar population with a low to intermediate
metallicity and a very bottom-heavy IMF does however adequately reproduce the
observed BCG halo colours. A bottom-heavy IMF also proves successful in
explaining a similar red excess observed in the halos of stacked edge-on disk
galaxies from the Sloan Digital Sky Survey. This may indicate that halos
dominated by low-mass stars is a phenomenon common to galaxies of very
different Hubble types.
