The M101 Satellite Luminosity Function and the Halo–Halo Scatter among Local Volume Hosts
The M101 Satellite Luminosity Function and the Halo–Halo Scatter among Local Volume Hosts
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DOI：
10.3847/1538-4357/ab46ab
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发表时间：
2019-06
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通讯作者：
P. Bennet;D. Sand;D. Crnojević;D. Crnojević;K. Spekkens;K. Spekkens;A. Karunakaran;D. Zaritsky;B. Mutlu-Pakdil
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作者：
P. Bennet;D. Sand;D. Crnojević;D. Crnojević;K. Spekkens;K. Spekkens;A. Karunakaran;D. Zaritsky;B. Mutlu-Pakdil
我们已经获得了深度哈勃太空望远镜(HST)对M101附近19个候选矮星系的成像。其中两个天体的高级巡天相机HST光度测量显示，已分解的恒星群和红巨星分支尖端的派生距离(D∼7MPC)与M101群成员资格一致。剩下的17个被发现没有分解的恒星群，这意味着它们要么是背景NGC5485星系的一部分，要么是遥远的低表面亮度(LSB)星系。值得注意的是，许多以前被认为是基于投影的M101群成员的LSB天体已经被证明是背景对象，这表明未来的漫射矮星调查在没有可靠的距离估计的情况下，在得出关于群成员的结论时需要非常谨慎。在这项工作中，我们根据这些新天体的存在更新了M101的卫星光度函数，直到MV=−8.2.M101是一个人烟稀少的系统，在MV≈−8之前只有9颗卫星，相比之下，M31有26颗卫星，本地卷中的主机为24.5士7.7.这使M101成为迄今为止探测到这个深度的最稀疏的组，尽管M94甚至比它被检查的深度更稀疏(MV=−9.1)。与所研究的其他局部体积星系相比，M101和M94有几个共同的特性，这使它们具有不同寻常的特点：它们的卫星数量非常少，但在这些卫星中也有很高的恒星形成比例；这些特性也在银河类似物周围卫星调查的星系中发现。我们认为，这些特性似乎与更广泛的银河系环境有关，越孤立的星系显示的卫星群越稀少，越有可能最近形成恒星，而那些处于密集环境中的星系有更多的卫星，往往没有正在进行的恒星形成。总体而言，我们的结果显示了类似质量的星系之间的晕到晕的散射水平，比在兰姆达冷暗物质模型中预测的要大。
We have obtained deep Hubble Space Telescope (HST) imaging of 19 dwarf galaxy candidates in the vicinity of M101. Advanced Camera for Surveys HST photometry for two of these objects showed resolved stellar populations and tip of the red giant branch derived distances (D ∼ 7 Mpc) consistent with M101 group membership. The remaining 17 were found to have no resolved stellar populations, meaning they are either part of the background NGC 5485 group or are distant low surface brightness (LSB) galaxies. It is noteworthy that many LSB objects that had previously been assumed to be M101 group members based on projection have been shown to be background objects, indicating the need for future diffuse dwarf surveys to be very careful in drawing conclusions about group membership without robust distance estimates. In this work we update the satellite luminosity function of M101 based on the presence of these new objects down to MV = −8.2. M101 is a sparsely populated system with only nine satellites down to MV ≈ −8, as compared with 26 for M31 and 24.5 ± 7.7 for the median host in the Local Volume. This makes M101 by far the sparsest group probed to this depth, although M94 is even sparser to the depth at which it has been examined (MV = −9.1). M101 and M94 share several properties that mark them as unusual compared with the other Local Volume galaxies examined: they have a very sparse satellite population but also have high star-forming fractions among these satellites; such properties are also found in the galaxies examined as part of the Satellites around Galactic Analogs survey. We suggest that these properties appear to be tied to the wider galactic environment, with more isolated galaxies showing sparse satellite populations that are more likely to have had recent star formation, while those in dense environments have more satellites that tend to have no ongoing star formation. Overall, our results show a level of halo-to-halo scatter between galaxies of similar mass that is larger than is predicted in the lambda cold dark matter model.