Milky Way’s Inner Stellar Halo and Thick Disk Formation

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The chemo-dynamical studies of the stellar halo near the Sun have shown the existence of streams, clumps and the interaction between orbital parameters and the stars’ chemical great amount in our Galaxy.

There has been found a new presence of elemental abundance sequences. Two different sequences in the color-magnitude diagram and a prominent, slightly retrograde kinematic structure were spotted near the big star while analyzing the stellar surveys. They can have a major accumulation event that was ever encountered in the Galaxy.

However, their part in the Galactic history is still unknown even with these observations. The kinematics, age, chemistry and spatial distribution of stars reports are connected to the two main Galactic components: the stellar halo and the thick disk.

The inner halo is proved to be governed by remains of an object which originally had a bigger mass than the Small Magellanic Cloud and was named as Gaia–Enceladus.

The stars that were born in Gaia–Enceladus cover up most of the sky, and their movements show the existence of the streams and direction that has the trajectory retrograde and extended.

The consolidation of the Milky Way with Gaia–Enceladus, which has a mass about four to one ratio, is the one that probably drove to the dynamical heating of the Galactic thick disk’s precursor. This merger also had a contribution, ten billion years ago, at the formation of the component. All this observations go in the same direction with the results of galaxy formation in the same time. This means that it expresses an outcome in advance that the inner stellar halo has to be governed by wastes from just a few progenitors that had a big mass.


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