Bo\'otes IV: A New Milky Way Satellite Discovered in the Subaru Hyper Suprime-Cam Survey and Implications for the Missing Satellite Problem
| Autor: | Hitoshi Murayama, Mikito Tanaka, Masashi Chiba, Nobuo Arimoto, Kohei Hayashi, Robert H. Lupton, Scott G. Carlsten, Daisuke Homma, Satoshi Miyazaki, Shiang-Yu Wang, Sakurako Okamoto, Yutaka Komiyama, Masayuki Tanaka, G. Torrealba, Michael A. Strauss, Miho N. Ishigaki |
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| Jazyk: | angličtina |
| Rok vydání: | 2019 |
| Předmět: |
Absolute magnitude
Physics Cosmology and Nongalactic Astrophysics (astro-ph.CO) Stellar population 010308 nuclear & particles physics Milky Way Dwarf galaxy problem FOS: Physical sciences Astronomy and Astrophysics BOOTES Astrophysics 01 natural sciences Astrophysics - Astrophysics of Galaxies Stars Space and Planetary Science Astrophysics of Galaxies (astro-ph.GA) Globular cluster 0103 physical sciences Satellite galaxy 010303 astronomy & astrophysics Astrophysics - Cosmology and Nongalactic Astrophysics |
| Popis: | We report on the discovery of a new Milky Way (MW) satellite in Bo\"otes based on data from the on-going Hyper Suprime-Cam (HSC) Subaru Strategic Program (SSP). This satellite, named Bo\"otes IV, is the third ultra-faint dwarf that we have discovered in the HSC-SSP. We have identified a statistically significant (32.3$\sigma$) overdensity of stars having characteristics of a metal-poor, old stellar population. The distance to this stellar system is $D_{\odot}=209^{+20}_{-18}$ kpc with a $V$-band absolute magnitude of $M_V=-4.53^{+0.23}_{-0.21}$ mag. Bo\"otes IV has a half-light radius of $r_h=462^{+98}_{-84}$ 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 $r_h=5.9^{+1.5}_{-1.3}$ pc located at $D_{\odot}=46^{+4}_{-4}$ kpc. Adopting the recent prediction for the total population of satellites in a MW-sized halo by Newton et al. (2018), which combined the characteristics of the observed satellites by SDSS and DES with the subhalos obtained in $\Lambda$CDM models, we estimate that there should be about two MW satellites at $M_V\le0$ in the $\sim676$ deg$^2$ covered by HSC-SSP, whereas that area includes six satellites. 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 $\Lambda$CDM theory overpredicts the number of satellites in a MW-sized halo. This may imply that the models need more refinements for the assignment of subhalos to satellites such as considering those found by the current deeper survey. [abridged] Comment: 13 pages, 11 figures, 2 tables, accepted for publication in PASJ |
| Databáze: | OpenAIRE |
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