标题： 关于银河晕的所谓对偶性 显示英文标题

标题： On the alleged duality of the Galactic halo

摘要： 我们基于Carollo等人(2007, 2010)的SDSS/SEGUE数据研究了银河晕的运动学。我们发现他们关于反向旋转晕的主张是由于距离估计存在显著偏差（约为50%）：所声称的反向旋转成分仅占整个样本的一小部分，容易受到污染，并被识别为距离高估的尾部。强烈的高估也导致垂直速度分量的提升，这解释了这些天体被声称达到的大高度。误差最严重的是低金属丰度恒星，这解释了人工成分的贫金属特性。我们还认为测量误差未被正确考虑，且对本质上非高斯的银河成分使用高斯拟合会导致识别出扭曲甚至人为的成分。我们对数据的评估导致对速度椭球的估计进行了修订，并未提供任何可靠的证据证明存在反向旋转的晕成分。如果存在一个独特的反向旋转晕成分，它必须比Carollo等人所声称的要弱得多。最后我们注意到，他们在Beers等人(2011)中提出的修正分析并未缓解我们的主要担忧。 显示英文摘要

摘要： We examine the kinematics of the Galactic halo based on SDSS/SEGUE data by Carollo et al. (2007, 2010). We find that their claims of a counter-rotating halo are the result of substantial biases in distance estimates (of order 50%): the claimed retrograde component, which makes up only a tiny fraction of the entire sample, prone to contaminations, is identified as the tail of distance overestimates. The strong overestimates also result in a lift in the vertical velocity component, which explains the large altitudes those objects were claimed to reach. Errors are worst for the lowest metallicity stars, which explains the metal-poor nature of the artificial component. We also argue that measurement errors were not properly accounted for and that the use of Gaussian fitting on intrinsically non-Gaussian Galactic components invokes the identification of components that are distorted or even artificial. Our evaluation of the data leads to a revision of the estimated velocity ellipsoids and does not yield any reliable evidence for a counterrotating halo component. If a distinct counterrotating halo component exists it must be far weaker than claimed by Carollo et al. Finally we note that their revised analysis presented in Beers et al. (2011) does not alleviate our main concerns.