Kaiki Taro INOUE
National Astron. Obs. Japan (NAOJ) (Tokyo, Japon)
in galactic halos may consist of MASsive Compact Objects (MASCOs) with
mass M=10^1-4 solar masses. Possible candidates for such compact objects
include primordial black holes or remnants of primordial (Population
III) stars. We propose a method for directly detecting MASCOs in
extragalactic halos, using the VLBI techniques with extremely high
resolution that will be achieved by the next generation mission of the
VLBI Space Observatory Program such as VSOP-2. If a galactic halo
comprising a large number of MASCOs produces multiple images of a
background radio-loud QSO by gravitational lensing, then a
high-resolution radio map of each macro-lensed image should reveal
microlensing effects by MASCOs. In the case of point-mass perturbers,
many tiny dark spots appear in the macro-lensed images associated
with a decrease in the surface brightness toward the fringe of the
original QSO image, whereas no such spots are seen in the SIS
models. Based on the size, position and magnified or demagnified
patterns of images, we shall be able to determine the mass and density
profile of an individual MASCO as well as its spatial distribution and
abundance in a galactic halo.
, Institut d'Astrophysique de Paris