2 research outputs found
Two Stellar Components in the Halo of the Milky Way
The halo of the Milky Way provides unique elemental abundance and kinematic
information on the first objects to form in the Universe, which can be used to
tightly constrain models of galaxy formation and evolution. Although the halo
was once considered a single component, evidence for its dichotomy has slowly
emerged in recent years from inspection of small samples of halo objects. Here
we show that the halo is indeed clearly divisible into two broadly overlapping
structural components -- an inner and an outer halo -- that exhibit different
spatial density profiles, stellar orbits and stellar metallicities (abundances
of elements heavier than helium). The inner halo has a modest net prograde
rotation, whereas the outer halo exhibits a net retrograde rotation and a peak
metallicity one-third that of the inner halo. These properties indicate that
the individual halo components probably formed in fundamentally different ways,
through successive dissipational (inner) and dissipationless (outer) mergers
and tidal disruption of proto-Galactic clumps.Comment: Two stand-alone files in manuscript, concatenated together. The first
is for the main paper, the second for supplementary information. The version
is consistent with the version published in Natur
Analysis of Star Formation in Galaxy-like Objects
Using cosmological hydrodynamical simulations, we investigate the effects of
hierarchical aggregation on the triggering of star formation in galactic-like
objects. We include a simple star formation model to transform the cold gas in
dense regions into stars. Simulations with different parameters have been
performed in order to quantify the dependence of the results on the parameters.
We then resort to stellar population synthesis models to trace the color
evolution of each object with red-shift and in relation to their merger
histories. We find that, in a hierarchical clustering scenario, the process of
assembling of the structure is one natural mechanism that may trigger star
formation.
The resulting star formation rate history for each individual galactic object
is composed of a continuous one () and a series of
star bursts.
We find that even the accretion of a small satellite can be correlated with a
stellar burst. Massive mergers are found to be more efficient at transforming
gas into starsComment: 11 postscript figures. 2000, ApJ, accepte