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

Creators: Komiyama, Yutaka; Chiba, Masashi; Tanaka, Mikito; Tanaka, Masayuki; Kirihara, Takanobu; Miki, Yohei; Mori, Masao; Lupton, Robert H.; Guhathakurta, Puragra; Kalirai, Jason S.; Gilbert, Karoline; Kirby, Evan; Lee, Myun Gyoon; Jang, In Sung; Sharma, Sanjib; Hayashi, Kohei

Abstract

We present wide and deep photometry of the northwestern part of the halo of the Andromeda galaxy (M31) using Hyper Suprime-Cam on the Subaru Telescope. The survey covers a 9.2 deg^2 field in the g, i, and NB515 bands and shows a clear red giant branch (RGB) of M31's halo stars and a pronounced red clump (RC) feature. The spatial distribution of RC stars shows a prominent stream feature, the Northwestern (NW) Stream, and a diffuse substructure in the southern part of our survey field. We estimate the distances based on the RC method and obtain (m-M) = 24.63 ± 0.191 (random) ± 0.057 (systematic) and 24.29 ± 0.211 (random) ± 0.057 (systematic) mag for the NW Stream and diffuse substructure, respectively, implying that the NW Stream is located behind M31, whereas the diffuse substructure is located in front of it. We also estimate line-of-sight distances along the NW Stream and find that the southern part of the stream is ~20 kpc closer to us relative to the northern part. The distance to the NW Stream inferred from the isochrone fitting to the color–magnitude diagram favors the RC-based distance, but the tip of the RGB (TRGB)-based distance estimated for NB515-selected RGB stars does not agree with it. The surface number density distribution of RC stars across the NW Stream is found to be approximately Gaussian with an FWHM of ~25 arcmin (5.7 kpc), with a slight skew to the southwest side. That along the NW Stream shows a complicated structure, including variations in number density and a significant gap in the stream.

Additional Information

© 2018 The American Astronomical Society. Received 2017 June 27; revised 2017 November 9; accepted 2017 December 8; published 2018 January 19. This work is supported in part by the JSPS Grant-in-Aid for Scientific Research (No. JP25287062, JP15K05037, JP25800098, JP25400222, and JP17H01101), MEXT Grant-in-Aid for Scientific Research on Innovative Areas (No. JP15H05892, JP16H01090 for K.H., JP16H01086 for M.C.), and Grant-in-Aid for JSPS Fellows (TK 26.348). P.G. was supported by NSF grant AST-1412648. M.G.L. and I.S.J. were supported by the National Research Foundation (NRF) grant funded by the Korea Government (NRF-2017R1A2B4004632). We would like to thank all the staff of Subaru Telescope, in particular Drs. Fumiaki Nakata, Tsuyoshi Terai, Shintaro Koshida, Francois Finet, and Akito Tajitsu for their excellent support during the observation, and all the staff of the HSC software developing group, in particular Dr. Hisanori Furusawa and Dr. Naoki Yasuda, for their advice during the processing of our M31 data. We would like to express our appreciation to Dr. Satoshi Kawanomoto for his effort in developing the NB515 filter. We are grateful to Dr. Paul Price for his kind support in calibrating our data to the PS1 system. We appreciate the many valuable comments and suggestions from the referee, which have improved this paper significantly. The numerical computations were carried out on the HA-PACS System in the Center for Computational Sciences, University of Tsukuba, Japan. The HSC collaboration includes the astronomical communities of Japan and Taiwan, and Princeton University. The HSC instrumentation and software were developed by the National Astronomical Observatory of Japan (NAOJ), the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU), the University of Tokyo, the High Energy Accelerator Research Organization (KEK), the Academia Sinica Institute for Astronomy and Astrophysics in Taiwan (ASIAA), and Princeton University. Funding was contributed by the FIRST program from the Japanese Cabinet Office, the Ministry of Education, Culture, Sports, Science and Technology (MEXT), the Japan Society for the Promotion of Science (JSPS), Japan Science and Technology Agency (JST), the Toray Science Foundation, NAOJ, Kavli IPMU, KEK, ASIAA, and Princeton University. This paper makes use of software developed for the Large Synoptic Survey Telescope. We thank the LSST Project for making their code freely available. The Pan-STARRS1 (PS1) Surveys have been made possible through contributions of the Institute for Astronomy, the University of Hawaii, the Pan-STARRS Project Office, the Max-Planck Society and its participating institutes, the Max Planck Institute for Astronomy and the Max Planck Institute for Extraterrestrial Physics, The Johns Hopkins University, Durham University, the University of Edinburgh, Queen's University Belfast, the Harvard-Smithsonian Center for Astrophysics, the Las Cumbres Observatory Global Telescope Network Incorporated, the National Central University of Taiwan, the Space Telescope Science Institute, the National Aeronautics and Space Administration under grant No. NNX08AR22G issued through the Planetary Science Division of the NASA Science Mission Directorate, the National Science Foundation under grant No. AST-1238877, the University of Maryland, and Eotvos Lorand University (ELTE).

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