How does deep Subaru imaging map the three-dimensional North-Western Stream?

Wide-field HSC imaging traces red-clump and red-giant stars in the north-western M31 halo.

Stellar Stream and Halo Structure in the Andromeda Galaxy from a Subaru/Hyper Suprime-Cam Survey

Stellar Stream and Halo Structure in the Andromeda Galaxy from a Subaru/Hyper Suprime-Cam Survey. Komiyama, Yutaka; Chiba, Masashi; Tanaka, Mikito; Tanaka, Masayuki; Kirihara, Takanobu; Miki, Yohei; Mori, Masao, et al., Astrophysical Journal, 853, 29 (2018).

arXiv:1712.03654 Publication · DOI

Approach

Photometry over 9.2 square degrees in g, i and NB515 is used to map substructure and estimate distances with stellar-population indicators.

Main result

Red-clump distances place the North-Western Stream behind M31 and a diffuse southern feature in front. The stream has internal distance and density variations, including a gap.

Scientific implications

These measurements constrain accretion geometry and provide spatial information for dynamical reconstructions of the stream.

Scope and limitations

Red-clump and red-giant-tip distance estimates do not fully agree. Population assumptions and foreground selection remain relevant systematics.