Why the Canis Major overdensity is not due to the Warp: analysis of its radial profile and velocities
Why the Canis Major overdensity is not due to the Warp: analysis of its radial profile and velocities
复制标题
为什么大犬座的密度过高不是由于扭曲造成的：对其径向轮廓和速度的分析
DOI：
10.1111/j.1365-2966.2004.08521.x
复制
发表时间：
2004
影响因子：
4.8
通讯作者：
A. McConnachie
中科院分区：
文献类型：
--
作者：
N. Martin;R. Ibata;B. Conn;G. Lewis;M. Bellazzini;M. Irwin;A. McConnachie
为了回应 Momany 等人的批评。 （2004），最近发现的大犬座（CMa）密度过高可以简单地用银河扭曲来解释，我们提出了 CMa 方向上存在恒星群体的证据，而这种恒星群体无法用已知的银河成分来解释。通过分析该方向上 M 巨星计数的径向分布，我们表明 Momany 等人。 (2004) 扭曲模型高估了北半球的恒星数量，因此隐藏了南半球的 CMa 特征。使用更好的扭曲模型对超密度的形态影响很小，并且清楚地显示了在 D = 7.2±0.3kpc 距离处分组的过量恒星。为了进一步支持不属于银盘的星群的存在，我们展示了 CMa 结构中心 M 巨星的径向速度，这些速度是通过 AAT 的 2dF 摄谱仪获得的。额外群体的径向速度为 vr = 109± 4kms 1 ，明显高于 CMa 距离处圆盘的典型速度。该群体的分散度也较低（13±4kms 1 ）。因此，大犬座的密度过高不太可能是由于银河扭曲造成的，这增加了我们正在观察一个正在分裂的矮星系或其残余物的假设。这引发了关于 CMa 的哪一部分之前被确定为亚空间以及如何解开这两个结构的问题。
In response to criticism by Momany et al. (2004), that the recently-identified Canis Major (CMa) overdensity could be simply explained by the Galactic warp, we present proof of the existence of a stellar population in the direction of CMa that cannot be explained by known Galactic components. By analyzing the radial distribution of counts of M-giant stars in this direction, we show that the Momany et al. (2004) warp model overestimates the number of stars in the Northern hemisphere, hence hiding the CMa feature in the South. The use of a better model of the warp has little influence on the morphology of the overdensity and clearly displays an excess of stars grouped at a distance of D = 7.2±0.3kpc. To lend further support to the existence of a population that does not belong to the Galactic disc, we present radial velocities of M-giant stars in the centre of the CMa structure that were obtained with the 2dF spectrograph at the AAT. The extra population shows a radial velocity of vr = 109± 4kms 1 , which is significantly higher than the typical velocity of the disc at the distance of CMa. This population also has a low dispersion (13± 4kms 1 ). The Canis Major overdensity is therefore highly unlikely to be due to the Galactic warp, adding weight to the hypothesis that we are observing a disrupting dwarf galaxy or its remnants. This leads to questions on what part of CMa was previously identified as the Warp and how to possibly disentangle the two structures.