Dynamics in the satellite system of Triangulum: is And XXII a dwarf satellite of M33?
Dynamics in the satellite system of Triangulum: is And XXII a dwarf satellite of M33?
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三角卫星系统的动力学：And XXII 是 M33 的矮卫星吗？
DOI：
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发表时间：
2012
期刊：
影响因子：
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通讯作者：
N. Tanvir
中科院分区：
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作者：
S. Chapman;Larry Widrow;M. Collins;J. Dubinski;R. Ibata;M. Rich;A. Ferguson;M. Irwin;G. Lewis;Nicolas F. Martin;A. McConnachie;J. Peñarrubia;N. Tanvir
我们目前的结果从光谱调查的矮球状AndXXII和两个扩展集群EC 1和EC2。这三个天体是三角座星系M33的候选卫星，而三角座星系本身很可能是M31的卫星。我们使用的深度成像多目标摄谱仪安装在THEAK-II望远镜，以获得径向速度的候选成员星，这些对象，从而确定最有可能的实际成员的恒星。11个最可能的恒星成员（13个候选者）被发现为AndXXII。我们得到AndXXII的速度色散上限为v < 6.0kms-1，金属丰度上限为（Fe/H）= 1.6，投影密度剖面的Plummer半径上限为255 pc.我们构造了AndXXII的彩色星等图，并确定了红巨星分支和水平分支。后者的位置被用来推导出与AndXXII的日心距离为853 ± 26 kpc。AndXXII的径向速度、距离和角位置的组合表明，它是M33的第一颗已知卫星的有力候选者，也是极少数星系卫星的例子之一。N体模拟表明，即使M31和M33在过去的几个Gyr中有过强烈的相遇，这个结论也不会改变。我们测试的假设，扩展集群突出潮汐剥离星系寻找一个多余的云晕状恒星在他们的附近。我们发现这样的云的情况下，EC 1，而不是EC2。这三个天体意味着M33的动力学质量与先前的估计一致。
We present results from a spectroscopic survey of the dwarf spheroidal AndXXII and the two extended clusters EC1 and EC2. These three objects are candidate satellites of the Triangulum galaxy, M33, which itself is likely a satellite of M31. We use the DEep Imaging Multi-Object Spectrograph mounted on the Keck-II telescope to derive radial velocities for candidate member stars of these objects and thereby identify the stars that are most likely actual members. Eleven most probable stellar members (of 13 candidates) are found for AndXXII. We obtain an upper limit ofv < 6.0kms 1 for the velocity dispersion of AndXXII, (Fe/H)� 1.6 for its metallicity, and 255pc for the Plummer radius of its projected density profile. We construct a colour magnitude diagram for AndXXII and identify both the red giant branch and the horizontal branch. The position of the latter is used to derive a heliocentric distance to AndXXII of 853 ±26kpc. The combination of the radial velocity, distance, and angular position of AndXXII indicates that it is a strong candidate for being the first known satellite of M33 and one of the very few examples of a galactic satellite of a satellite. N- body simulations imply that this conclusion is unchanged even if M31 and M33 had a strong encounter in the past few Gyr. We test the hypothesis that the extended clusters highlight tidally stripped galaxies by searching for an excess cloud of halo-like stars in their vicinity. We find such a cloud for the case of EC1 but not EC2. The three objects imply a dynamical mass for M33 that is consistent with previous estimates.