Oral Presentation
Statistical properties of substructures around MW-size halos and their implications for the formation of stellar streams
Presenter: Yu Morinaga (Chiba University)
Stellar streams originating in disrupted dwarf galaxies and star clusters are observed around the Milky Way and nearby galaxies. Such substructures are the important tracers that record how the host halos accreted progenitor galaxies. To investigate the relationship between structural properties of substructures and orbits of their progenitors, we combine semi-analytic models with a high-resolution cosmological N body simulation and analyze the statistical properties of a large sample of substructures around Milky Way size halos. Using `Particle Tagging' method, we embed stellar components in progenitor halos and trace the phase space distribution of the substructures down to z=0. Additionally, we use a semi-analytic model to assign stellar masses to the progenitors and successfully reproduce the stellar mass function of observed dwarf galaxies around the Milky Way and the Andromeda galaxy. We characterize structural properties of the substructures such as length and thinness at z=0 and explore the relationship between them and the orbits of progenitors. We find that the distributions of length and thinness of substructures vary smoothly as pericenter and apocenter of the progenitors. The progenitors with small pericenter are strongly perturbed by the tidal force from their host halos and get thicker by z=0. We also find that the length and thinness of substructures vary smoothly as the redshift when the host halos accrete their progenitors. For substructures observed like streams at z=0, a large part of the progenitors is accreted by their host halos at redshift 0.52 are entirely disrupted by z=0 and cannot be observed as streams.
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