The Milky Way tomography with Subaru Hyper Suprime-Cam. I. Halo substructures
Komiyama, Yutaka; Takada, Masahiro; Tanaka, Masayuki; Carlsten, Scott G.; Hayashi, Kohei; Chiba, Masashi; Suzuki, Yoshihisa; Fukushima, Tetsuya; Tokiwa, Akira; Qiu, Tian
Japan, United States
Abstract
We analyze the photometric data in the Wide layer of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) over ~1200 deg2 to uncover new halo substructures beyond the distance, D⊙ ~ 30 kpc, from the Sun. For this purpose, we develop an isochrone filter for an old, metal-poor stellar system to extract the faint main-sequence stars at a range of distances. With this method, we detect not only the previously discovered substructures such as the Orphan Stream, but also a new overdensity toward Boötes at about D⊙ ~ 60 kpc and a new stream-like feature toward Pisces at around D⊙ ~ 60 kpc. It has been suggested that a small-scale overdensity exists in this direction of Pisces (the so-called Pisces Overdensity), but our results show that the overdensity is widely spread with a tidally elongated feature. Combining our results with the ongoing Hyper Suprime-Cam narrow-band survey and the near-future spectroscopic survey with Prime Focus Spectrograph (PFS) will allow us to place strong constraints on the origin of these halo substructures.