Red Halos of Galaxies — Reservoirs of Baryonic Dark Matter?

摘要

Deep optical/near-IR surface photometry of galaxies outside the Local Group haverevealed faint and very red halos around objects as diverse as disk galaxies and starburstingdwarf galaxies. The colours of these structures are too extreme to be reconciled with stellarpopulations similar to those seen in the stellar halos of the Milky Way or M31, and alternativeexplanations like dust reddening, high metallicities or nebular emission are also disfavoured. Astellar population obeying an extremely bottom-heavy initial mass function (IMF), is on theother hand consistent with all available data. Because of its high mass-to-light ratio, such apopulation would effectively behave as baryonic dark matter and could account for some of thebaryons still missing in the low-redshift Universe. Here, we give an overview of current red halodetections, alternative explanations for the origin of the red colours and ongoing searches for redhalos around types of galaxies for which this phenomenon has not yet been reported. A numberof potential tests of the bottom-heavy IMF hypothesis are also discussed.