Issue |
A&A
Volume 469, Number 2, July II 2007
|
|
---|---|---|
Page(s) | 387 - 404 | |
Section | Cosmology (including clusters of galaxies) | |
DOI | https://doi.org/10.1051/0004-6361:20066017 | |
Published online | 24 April 2007 |
Limits on the Macho content of the Galactic Halo from the EROS-2 Survey of the Magellanic Clouds *,**
1
CEA, DSM, DAPNIA, Centre d'Études de Saclay, 91191 Gif-sur-Yvette Cedex, France
2
Laboratoire de l'Accélérateur Linéaire, IN2P3 CNRS, Université de Paris-Sud, 91405 Orsay Cedex, France
3
The Niels Bohr Institute, Copenhagen University, Juliane Maries Vej 30, 2100 Copenhagen, Denmark
4
Institut d'Astrophysique de Paris, UMR 7095 CNRS, Université Pierre & Marie Curie, 98 bis boulevard Arago, 75014 Paris, France
5
Observatoire Midi-Pyrénées, Laboratoire d'Astrophysique (UMR 5572), 14 av. E. Belin, 31400 Toulouse, France
6
European Southern Observatory (ESO), Casilla 19001, Santiago 19, Chile
7
Department of Astronomy, Ohio State University, Columbus, OH 43210, USA
8
Observatoire de Marseille, 2 place Le Verrier, 13248 Marseille Cedex 04, France
Received:
11
July
2006
Accepted:
10
April
2007
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
stars in the Magellanic clouds for microlensing
events caused by such objects.
Methods.
In this work, we use only a subsample of bright stars
spread over
of the LMC and
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 .
Combined with the results of EROS-1,
this implies that the optical depth toward the
Large Magellanic Cloud (LMC)
due to such lenses is
(95% CL), corresponding
to a fraction of the halo mass of less than 8%.
This optical depth is considerably less than that
measured by the MACHO collaboration in the central region
of the LMC.
More generally, machos in the
mass range
are ruled out
as the primary occupants of the Milky Way Halo.
Key words: Galaxy: halo / cosmology: dark matter / gravitational lensing
© ESO, 2007
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