The Red Halo Phenomenon

Optical and near-IR observations of the halos of disk galaxies and bluecompact galaxies have revealed a very red spectral energy distribution, whichcannot easily be reconciled with a normal, metal-poor stellar population likethat in the stellar halo of the Milky Way. Here, spectral evolutionary modelsare used to explore the consequences of these observations. We demonstrate thata stellar population of low to intermediate metallicity, but with an extremelybottom-heavy initial mass function, can explain the red halos around both typesof objects. Other previously suggested explanations, like nebular emission orvery metal-rich stars, are shown to fail in this respect. This indicates that,if the reported halo colours are correct, halo populations dominated bylow-mass stars may be a phenomenon common to galaxies of very different Hubbletypes. Potential tests of this hypothesis are discussed, along with itsimplications for the baryonic dark matter content of galaxies.Comment: 6 pages, 3 figures, Accepted for publication in Ap