Final results for mapping the Milky Way's stellar halo with blue horizontal-branch stars selected from the Subaru Hyper Supreme-Cam Survey

Tetsuya Fukushima; Masashi Chiba; Mikito Tanaka; Kohei Hayashi; Daisuke Homma; Sakurako Okamoto; Yutaka Komiyama; Masayuki Tanaka; Nobuo Arimoto; Tadafumi Matsuno

arXiv · 2406.11923

Final results for mapping the Milky Way's stellar halo with blue horizontal-branch stars selected from the Subaru Hyper Supreme-Cam Survey

Tetsuya Fukushima·Masashi Chiba·Mikito Tanaka·Kohei Hayashi·Daisuke Homma·Sakurako Okamoto·Yutaka Komiyama·Masayuki Tanaka·Nobuo Arimoto·Tadafumi Matsuno

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Abstract

We select blue-horizontal branch stars (BHBs) from the internal data release of the Hyper Suprime-Cam Subaru Strategic Program to reveal the global structure of the Milky Way (MW) stellar halo. The data are distributed over $\sim 1,100$~deg$^2$ area in the range of $18.5 r_{\rm b}$; the statistical difference between these fitting profiles is small. Both profiles are found to show prolate shapes having axial ratios of $q=1.47^{+0.30}_{-0.33}$ and $1.56^{+0.34}_{-0.23}$, respectively. We also find a signature of the so-called "splashback radius" for the candidate BHBs, which can reach as large as $r \sim 575$~kpc, although it is still inconclusive owing to rather large distance errors in this faintest end of the sample. Our results suggest that the MW stellar halo consists of the two overlapping components: the {\it in situ} inner halo showing a relatively steep radial density profile and the {\it ex situ} outer halo with a shallower profile, being characteristic of a component formed from accretion of small stellar systems.

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Tetsuya Fukushima, Masashi Chiba, Mikito Tanaka, Kohei Hayashi, Daisuke Homma, Sakurako Okamoto, Yutaka Komiyama, Masayuki Tanaka, Nobuo Arimoto, Tadafumi Matsuno. 2024-06-17. Final results for mapping the Milky Way's stellar halo with blue horizontal-branch stars selected from the Subaru Hyper Supreme-Cam Survey. https://arxiv.org/abs/2406.11923

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