A Two Micron All Sky Survey View of the Sagittarius Dwarf Galaxy. I. Morphology of the Sagittarius Core and Tidal Arms
A Two Micron All Sky Survey View of the Sagittarius Dwarf Galaxy. I. Morphology of the Sagittarius Core and Tidal Arms
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DOI：
10.1086/379504
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发表时间：
2003-04
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影响因子：
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通讯作者：
S. Majewski;M. Skrutskie;M. Weinberg;J. A. I. U. O. Virginia;U. Massachusetts
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作者：
S. Majewski;M. Skrutskie;M. Weinberg;J. A. I. U. O. Virginia;U. Massachusetts
我们展示了人马座（Sgr）矮星系的第一个全天视图，该视图是由完整的两微米全天巡天（2MASS）中探测到的m巨星示踪剂绘制的。对人马座突出的m巨星群进行近红外测光，可以前所未有地清晰地看到人马座的中心。主体具有限制长轴半径30°的King剖面-比先前发现或假设的要大得多-在此之上是Sgr潮尾中恒星密度剖面的显著断裂；因此，人马座的径向轮廓类似于星系矮蛛形（dSph）卫星。采用传统的dSph光谱分析方法，我们确定Sgr主体的亮度为MV = -13.27（已知的银河系dSph星系中最亮的），Sgr的总质量光比为25太阳单位。然而，我们对后一种结果持怀疑态度，并认为在King-fit核心半径（224'）之外观察到的大部分结构可能超出了实际的Sgr潮汐半径，因为前矮螺旋/不规则卫星在其最后轨道上经历了灾难性的破坏。人马座的m -巨星分布在与球状星团M54的老恒星相同的位置有一个中心密度尖峰，但不是由于这个位置。我们发现一条引人注目的潮汐尾从人马座中心延伸出来，并以大约恒定的密度和平均距离从~20到40kpc不等的弧线横跨银河系南半球。一个突出的前导碎片臂从人马座中心向北的银面延伸到距离太阳约45千公里的离星系带，然后转向北银冠（NGC），从那里它下降回银面，变得缩短，并且在更亮的时候覆盖了NGC。前尾和后尾的人马座彗尾位于银河系中心周围一个明确的轨道平面上。太阳位于距离这个平面1千秒的范围内，靠近人马座的主要碎片的路径；因此，有可能以前的人马座恒星在太阳附近或在太阳附近。我们讨论了这一关于人马座星系及其内脏的新观点对人马座星系轨道、质量、质量损失率以及恒星对银河系晕的贡献的影响。Sgr潮汐碎片沿其倾斜轨道显示的最小进动支持了接近球形银河系潜力的概念。Sgr尾部的M巨星数量至少是Sgr主体的King极限半径范围内的15%。M巨星，据推测是在过去的几十亿年里在Sgr核心形成的，然而在Sgr潮臂上分布如此广泛，这一事实不仅限制了这些潮臂的动力学年龄，而且还提出了一个时间问题，这个问题与Sgr核心最近的结合能有关，而最近灾难性的质量损失最自然地解释了这一点。尽管麦哲伦星云中有大量的M巨星，但Sgr似乎贡献了高纬度光环M巨星的75%以上。没有证据表明麦哲伦星云中有扩展的m巨星潮汐碎片。一般来说，在人马座系统的m巨星全天图和之前公布的所有潜在的人马座碎片之间发现了良好的对应关系，除了人马座碳星，与其他银河系卫星的对应物相比，它必须是亚光的，以解决差异。
We present the first all-sky view of the Sagittarius (Sgr) dwarf galaxy mapped by M-giant star tracers detected in the complete Two Micron All Sky Survey (2MASS). Near-infrared photometry of Sgr's prominent M-giant population permits an unprecedentedly clear view of the center of Sgr. The main body is fitted with a King profile of limiting major-axis radius 30°—substantially larger than previously found or assumed—beyond which is a prominent break in the density profile from stars in the Sgr tidal tails; thus the Sgr radial profile resembles that of Galactic dwarf speroidal (dSph) satellites. Adopting traditional methods for analyzing dSph light profiles, we determine the brightness of the main body of Sgr to be MV = -13.27 (the brightest of the known Galactic dSph galaxies) and the total Sgr mass-to-light ratio to be 25 in solar units. However, we regard the latter result with suspicion and argue that much of the observed structure beyond the King-fit core radius (224') may be outside the actual Sgr tidal radius as the former dwarf spiral/irregular satellite undergoes catastrophic disruption during its last orbits. The M-giant distribution of Sgr exhibits a central density cusp at the same location as, but not due to, the old stars constituting the globular cluster M54. A striking trailing tidal tail is found to extend from the Sgr center and arc across the south Galactic hemisphere with approximately constant density and mean distance varying from ~20 to 40 kpc. A prominent leading debris arm extends from the Sgr center northward of the Galactic plane to an apogalacticon ~45 kpc from the Sun and then turns toward the north Galactic cap (NGC), from where it descends back toward the Galactic plane, becomes foreshortened, and, at brighter magnitudes, covers the NGC. The leading and trailing Sgr tails lie along a well-defined orbital plane about the Galactic center. The Sun lies within a kiloparsec of that plane and near the path of leading Sgr debris; thus, it is possible that former Sgr stars are near or in the solar neighborhood. We discuss the implications of this new view of the Sgr galaxy and its entrails for the character of the Sgr orbit, mass, mass-loss rate, and contribution of stars to the Milky Way halo. The minimal precession displayed by the Sgr tidal debris along its inclined orbit supports the notion of a nearly spherical Galactic potential. The number of M giants in the Sgr tails is at least 15% that contained within the King limiting radius of the main Sgr body. The fact that M giants, presumably formed within the past few gigayears in the Sgr nucleus, are nevertheless so widespread along the Sgr tidal arms not only places limits on the dynamical age of these arms but also poses a timing problem that bears on the recent binding energy of the Sgr core and that is most naturally explained by recent and catastrophic mass loss. Sgr appears to contribute more than 75% of the high-latitude, halo M giants, despite substantial reservoirs of M giants in the Magellanic Clouds. No evidence of extended M-giant tidal debris from the Magellanic Clouds is found. Generally good correspondence is found between the M-giant, all-sky map of the Sgr system and all previously published detections of potential Sgr debris, with the exception of Sgr carbon stars, which must be subluminous compared with counterparts in other Galactic satellites in order to resolve the discrepancy.