EROS and MACHO Combined Limits on Planetary-Mass Dark Matter in the Galactic Halo

Abstract

The EROS and MACHO collaborations have each published upper limits on the amount of planetary-mass dark matter in the Galactic halo obtained from gravitational microlensing searches. In this Letter, the two limits are combined to give a much stronger constraint on the abundance of low-mass MACHOs. Specifically, objects with masses 10⁻⁷ M m10⁻³ M make up less than 25% of the halo dark matter for most models considered, and less than 10% of a standard spherical halo is made of MACHOs in the 3.5×10⁻⁷ M<m−5 M mass range.