The hidden giant: discovery of an enormous Galactic dwarf satellite in Gaia DR2
The hidden giant: discovery of an enormous Galactic dwarf satellite in Gaia DR2
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DOI：
10.1093/mnras/stz1624
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发表时间：
2018-11
影响因子：
4.8
通讯作者：
G. Torrealba;V. Belokurov;Sergey E. Koposov;T. Li;M. Walker;J. Sanders;A. Geringer-Sameth;D. Zucker
中科院分区：
文献类型：
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作者：
G. Torrealba;V. Belokurov;Sergey E. Koposov;T. Li;M. Walker;J. Sanders;A. Geringer-Sameth;D. Zucker
我们报道在安特利亚星座发现了一颗银河系卫星。Antlia 2矮星系位于银盘后面，纬度为b∼11°，跨度为1.2 6°，相当于距离为130kpc的∼2.9kpc。虽然在空间范围上与大麦哲伦星云相似，但安特利亚2号在mv=−9mag时要暗几个数量级，使其成为迄今已知的最低表面亮度系统(∼31.9argsec−2)，∼扩散程度是所谓的超扩散星系的100倍。这颗卫星是通过综合天文测量、光度测量和GAIA数据发布2中的变异性数据确定的，其性质也得到了深度档案DECAM成像的确认，该成像显示了一个明显的BHB信号。我们还利用AAOmega获得了对AAT的跟踪光谱，识别了159颗成员星，并用它们测量了矮星的系统速度，S−1，速度色散，S−，和平均金属丰度，[Fe/H]=−1.4。根据这些性质，我们得出结论，安特利亚2号是迄今探测到的密度最低的暗物质(DM)光晕之一。动力学模型和潮汐扰乱模拟表明，岩心DM剖面和强潮汐剥离的组合可以解释这颗卫星的观测特性。这个核心的起源可能与激进的反馈一致，甚至可能需要替代冷暗物质(如超轻玻色子)。
We report the discovery of a Milky Way satellite in the constellation of Antlia. The Antlia 2 dwarf galaxy is located behind the Galactic disc at a latitude of b ∼ 11° and spans 1.26°, which corresponds to ∼2.9 kpc at its distance of 130 kpc. While similar in spatial extent to the Large Magellanic Cloud, Antlia 2 is orders of magnitude fainter at MV = −9 mag, making it by far the lowest surface brightness system known (at ∼31.9 mag arcsec−2), ∼100 times more diffuse than the so-called ultra diffuse galaxies. The satellite was identified using a combination of astrometry, photometry, and variability data from Gaia Data Release 2, and its nature confirmed with deep archival DECam imaging, which revealed a conspicuous BHB signal. We have also obtained follow-up spectroscopy using AAOmega on the AAT, identifying 159 member stars, and we used them to measure the dwarf’s systemic velocity, 290.9 ± 0.5 km s−1, its velocity dispersion, 5.7 ± 1.1 km s−1, and mean metallicity, [Fe/H] = −1.4. From these properties we conclude that Antlia 2 inhabits one of the least dense dark matter (DM) haloes probed to date. Dynamical modelling and tidal-disruption simulations suggest that a combination of a cored DM profile and strong tidal stripping may explain the observed properties of this satellite. The origin of this core may be consistent with aggressive feedback, or may even require alternatives to cold dark matter (such as ultra-light bosons).