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The Local Group dwarf spheroidal galaxies:
A key to the building blocks in the Universe
H. Hirashita et al.
Kyoto University, Japan
Recent studies have been revealing the dark matter content in
dwarf spheroidal galaxies (dSphs). Their low mass ( 10 7 {
10 8
M ) indicates that the dSphs may provide a clue to physical
properties of the building blocks in the hierarchical structure for-
mation. In this scenario, the collapse of such low-mass objects
is considered to form the rst luminous objects and their forma-
tion epoch depends on the cosmological parameters. As a key to
structure formation, thus, we consider what determines the phys-
ical properties of dSphs.
We select the Local Group dSphs as a sample. To obtain the in-
formation on the star formation history of dSphs, we investigate
the relation between their metallicity and virial mass. According
to our scenario, the star formation eфciency of the dSphs is low,
which is also supported by their high mass-to-light ratios. Envi-
ronmental eects on the dSphs is also investigated. A dSph near
to a giant galaxy suers ram pressure stripping, if galactic wind
blows from the giant galaxy. However, we nd no observational
evidence that the tidal forces by giant galaxies aect the density
proles of the dSphs, which indicates that the stellar systems of
the dSphs lie in their deep dark matter potentials.
Co-authors: N. Tamura & T. T. Takeuchi.
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