Abstract
Stellar streams are stars which are trapped in the same potensial caused by dynamical resonance or tidal force. We aim to analyze kinematic sub- structures (streams) in the Galactic halo by V vs √ U2+ 2V 2 planes of Arifyanto & Fuchs. We crossmatched data from Gaia DR2, GALAH DR2, RAVE DR5 and LAMOST DR4 based on positions. We have 3D kinematics and metallicity data of halo stars selected from kinematics criteria from ratio of probability of thick disk (TD) over halo (H) less than 0.01. Substructures are detected by using wavelet transformation and corrected using 15 Monte Carlo simulations. We obtained four kinematic structures on V vs √U2 + 2V 2 plane which two of them are associated to BB17-1 and BB17-2 streams. All the streams had a high probability from the extragalactic origin.
Highlights
There are two scenarios of galactic formation
A galaxy is formed from the same protogalaxy cloud which collapsed and every part of galaxy, such as bulge, disk, and halo, is formed at the same time
Hierarchical scenario is supported by a proof that Sagittarius dwarf spheroidal (Sgr dSph) deformed because of tidal force from Galactic center [3]
Summary
There are two scenarios of galactic formation. First is monolithic collapse by Eggen, LyndenBell, and Sandage [1]. This scenario can explain that stars in bulge, disk, and halo have different typical age. In 1978, Eggen introduced "retrograde group," stars that expected came from ω Centauri cluster [6].
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