Botes. IV. A new Milky Way satellite discovered in the Subaru Hyper Suprime-Cam Survey and implications for the missing satellite problem
Botes. IV. A new Milky Way satellite discovered in the Subaru Hyper Suprime-Cam Survey and implications for the missing satellite problem
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博特斯。
DOI：
10.1093/pasj/psz076
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发表时间：
2019
影响因子：
2.3
通讯作者：
Murayama Hitoshi
中科院分区：
文献类型：
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作者：
Homma Daisuke;Chiba Masashi;Komiyama Yutaka;Tanaka Masayuki;Okamoto Sakurako;Tanaka Mikito;Ishigaki Miho N;Hayashi Kohei;Arimoto Nobuo;Carlsten Scott G;Lupton Robert H;Strauss Michael A;Miyazaki Satoshi;Torrealba Gabriel;Wang Shiang-Yu;Murayama Hitoshi
我们根据正在进行的超级超级凸轮（HSC）斯巴鲁战略计划（SSP）的数据报告在牧夫座发现了一颗新的银河系（MW）卫星。这颗名为牧夫座IV的卫星是我们在HSC-SSP中发现的第三颗超暗矮星。我们已经发现了统计上显着的（32.3σ）过密度恒星，具有贫金属、古老恒星群的特征。这个恒星系统的距离为千秒差距，V波段绝对星等为等。牧夫座IV的半光半径为pc，椭圆率为，这清楚地表明它是一个矮卫星星系。我们还发现了另一个高密度的星团，它看起来像是一个昏暗的球状星团，其等长和秒长都在千秒差距。采用牛顿等人最近对兆瓦级光环中卫星总数的预测。（，MNRAS，479，2853），结合斯隆数字巡天和暗能量巡天观测到的卫星特征和ΛCDM模式获得的晕，我们估计在HSC-SSP覆盖的1676 deg 2范围内应该有两颗MV ≤ 0的MW卫星，而该区域包括六颗卫星（六分仪，狮子座IV，飞马座III，鲸鱼座III，处女座I，和Bootes IV）。因此，观测到的卫星数量大于理论预测。从表面上看，我们有一个卫星太多的问题，而不是众所周知的卫星丢失问题，即ΛCDM理论高估了MW大小的光环中的卫星数量。这可能意味着，模型需要进一步完善，以分配subhalos的卫星，如考虑到目前的更深的调查发现。在规划的1400 deg 2区域内对HSC-SSP进行进一步调查，将对这一问题产生更强的统计约束。
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 iskpc with aV-band absolute magnitude ofmag. Boötes IV has a half-light radius ofpc and an ellipticity of, which clearly suggests that this is a dwarf satellite galaxy. We also found another overdensity that appears to be a faint globular cluster withmag andpc located atkpc. Adopting the recent prediction for the total population of satellites in a MW-sized halo by Newton et al. (, 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 atMV≤ 0 in the ∼676 deg2covered 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 deg2area.