Limits on the Macho content of the Galactic Halo from the EROS-2 Survey of the Magellanic Clouds
Aims: The EROS-2 project was designed to test the hypothesis that massive compact halo objects (the so-called “machos”) could be a major component of the dark matter halo of the Milky Way galaxy. To this end, EROS-2 monitored over 6.7 years 33×106 stars in the Magellanic clouds for microlensing events caused by such objects.
Methods: In this work, we use only a subsample of 7×106 bright stars spread over 84 deg2 of the LMC and 9 deg2 of the SMC. The strategy of using only bright stars helps to discriminate against background events due to variable stars and allows a simple determination of the effects of source confusion (blending). The use of a large solid angle makes the survey relatively insensitive to effects that could make the optical depth strongly direction dependent.
Results: Using this sample of bright stars, only one candidate event was found, whereas ~39 events would have been expected if the Halo were entirely populated by objects of mass M∼0.4~M⊙. Combined with the results of EROS-1, this implies that the optical depth toward the Large Magellanic Cloud (
Astronomy and Astrophysics
- Pub Date:
- July 2007
- Galaxy: halo;
- cosmology: dark matter;
- gravitational lensing;
- 22 pages, 20 figures, accepted A&