Oral Presentation
Stellar population and motion in the Galactic halo substructure using HSC and Gaia data
Presenter: Yoshihisa Suzuki (Astronomical Institute, Tohoku University)
Within the stellar halo of our Milky Way (MW) galaxy, there are substructures such as stellar streams and overdensities, which are key to understanding the formation history of the MW. This is because the characteristics of the substructures are inscribed with information about past dwarf galaxy mergers and accretion events that had a significant impact on the formation of the MW stellar halo.
Since the release of the Sloan Digital Sky Survey (SDSS) data, the study of the substructure of the MW has received much attention from the observational side. One of the substructures discovered by the extensive systematic photometric observations of SDSS is Virgo OverDensity (VOD). The VOD is thought to be an overdensity within the Sagittarius stream, which was formed by the Sagittarius dwarf galaxy being stretched by tidal forces during its accretion to the MW. However, the characteristics of its stellar population and its motion in the MW stellar halo remain unresolved.
In order to unravel these questions, we used Hyper Suprime-Cam (HSC) data in combination with Gaia satellite data. Isochrone fitting using the theoretical curve of stellar evolution was performed on the color-magnitude diagram drawn using the HSC data, and restrictions on stellar population such as the age and metallicity of VOD were given. As a result, it was confirmed that there is a spatial gradient in the stellar population within the VOD region. In combination with the proper motion data of Gaia, the results suggest that these stellar population are different from the viewpoint of motion.
In this talk, I will compare these results with those of the Sagittarius Tidal Stream model by Law and Majewski (2010), and provide observational constraints on the past orbital motion of the Sagittarius dwarf galaxy progenitor.
asiaa.sinica.edu.tw