TY - JOUR
T1 - Boötes. IV. A new Milky Way satellite discovered in the Subaru Hyper Suprime-Cam Survey and implications for the missing satellite problem
AU - Homma, Daisuke
AU - Chiba, Masashi
AU - Komiyama, Yutaka
AU - Tanaka, Masayuki
AU - Okamoto, Sakurako
AU - Tanaka, Mikito
AU - Ishigaki, Miho N.
AU - Hayashi, Kohei
AU - Arimoto, Nobuo
AU - Carlsten, Scott G.
AU - Lupton, Robert H.
AU - Strauss, Michael A.
AU - Miyazaki, Satoshi
AU - Torrealba, Gabriel
AU - Wang, Shiang Yu
AU - Murayama, Hitoshi
N1 - Funding Information:
This work makes use of data collected at the Subaru Telescope and retrieved from the HSC data archive system, which is operated by Subaru Telescope and Astronomy Data Center at National Astronomical Observatory of Japan. MC thanks support from MEXT Grant-in-Aid for Scientific Research on Innovative Areas (Nos. 15H05889, 16H01086, 18H04334). NA is supported by the Brain Pool Program, which is funded by the Ministry of Science and ICT through the National Research Foundation of Korea (2018H1D3A2000902).
Funding Information:
The 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, Heidelberg and the Max Planck Institute for Extraterrestrial Physics, Garching, 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 and the Los Alamos National Laboratory.
Funding Information:
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 Japanese Cabinet Office, the Ministry of Education, Culture, Sports, Science and Technology, the Japan Society for the Promotion of Science, Japan Science and Technology Agency, the Toray Science Foundation, NAOJ, Kavli IPMU, KEK, ASIAA, and Princeton University.
Publisher Copyright:
© 2019 The Author(s). Published by Oxford University Press on behalf of the Astronomical Society of Japan.
PY - 2019/10/1
Y1 - 2019/10/1
N2 - We report on the discovery of a new Milky Way (MW) satellite in Boötes based on data from the ongoing Hyper Suprime-Cam (HSC) Subaru Strategic Program (SSP). This satellite, named Boötes IV, is the third ultra-faint dwarf that we have discovered in the HSC-SSP. We have identified a statistically significant (32.3σ) overdensity of stars with characteristics of a metal-poor, old stellar population. The distance to this stellar system is D⊙ =209+20-18\:kpc with a V-band absolute magnitude of M-V=-4.53+0.23-0.21\:mag. Boötes IV has a half-light radius of rh=462+98-84\:pc and an ellipticity of 0.64+0.05-0.05, which clearly suggests that this is a dwarf satellite galaxy. We also found another overdensity that appears to be a faint globular cluster with M-V=-0.20+0.59-0.83\:mag and rh=5.9+1.5-1.3\:pc located at D⊙ =46+4-4\:kpc. Adopting the recent prediction for the total population of satellites in a MW-sized halo by Newton et al. (2018, MNRAS, 479, 2853), which combined the characteristics of the satellites observed by the Sloan Digital Sky Survey and the Dark Energy Survey with the subhalos obtained in ΛCDM models, we estimate that there should be about two MW satellites at MV ≤ 0 in the ∼676 deg2 covered by HSC-SSP, whereas that area includes six satellites (Sextans, Leo IV, Pegasus III, Cetus III, Virgo I, and Boötes IV). Thus, the observed number of satellites is larger than the theoretical prediction. On the face of it, we have a problem of too many satellites, instead of the well-known missing satellites problem whereby the ΛCDM theory overpredicts the number of satellites in a MW-sized halo. This may imply that the models need more refinement for the assignment of subhalos to satellites, such as considering those found by the current deeper survey. More statistically robust constraints on this issue will be brought by further surveys of HSC-SSP over the planned ∼1400 deg2 area.
AB - We report on the discovery of a new Milky Way (MW) satellite in Boötes based on data from the ongoing Hyper Suprime-Cam (HSC) Subaru Strategic Program (SSP). This satellite, named Boötes IV, is the third ultra-faint dwarf that we have discovered in the HSC-SSP. We have identified a statistically significant (32.3σ) overdensity of stars with characteristics of a metal-poor, old stellar population. The distance to this stellar system is D⊙ =209+20-18\:kpc with a V-band absolute magnitude of M-V=-4.53+0.23-0.21\:mag. Boötes IV has a half-light radius of rh=462+98-84\:pc and an ellipticity of 0.64+0.05-0.05, which clearly suggests that this is a dwarf satellite galaxy. We also found another overdensity that appears to be a faint globular cluster with M-V=-0.20+0.59-0.83\:mag and rh=5.9+1.5-1.3\:pc located at D⊙ =46+4-4\:kpc. Adopting the recent prediction for the total population of satellites in a MW-sized halo by Newton et al. (2018, MNRAS, 479, 2853), which combined the characteristics of the satellites observed by the Sloan Digital Sky Survey and the Dark Energy Survey with the subhalos obtained in ΛCDM models, we estimate that there should be about two MW satellites at MV ≤ 0 in the ∼676 deg2 covered by HSC-SSP, whereas that area includes six satellites (Sextans, Leo IV, Pegasus III, Cetus III, Virgo I, and Boötes IV). Thus, the observed number of satellites is larger than the theoretical prediction. On the face of it, we have a problem of too many satellites, instead of the well-known missing satellites problem whereby the ΛCDM theory overpredicts the number of satellites in a MW-sized halo. This may imply that the models need more refinement for the assignment of subhalos to satellites, such as considering those found by the current deeper survey. More statistically robust constraints on this issue will be brought by further surveys of HSC-SSP over the planned ∼1400 deg2 area.
KW - Local Group
KW - galaxies: dwarf
KW - galaxies: individual (Boötes IV)
KW - globular clusters: individual (HSC 1)
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U2 - 10.1093/pasj/psz076
DO - 10.1093/pasj/psz076
M3 - Article
AN - SCOPUS:85074427036
SN - 0004-6264
VL - 71
JO - Publication of the Astronomical Society of Japan
JF - Publication of the Astronomical Society of Japan
IS - 5
M1 - 94
ER -