Spitzer观测的边缘螺旋星系中弯曲的开始
The onset of warps in Spitzer observations of edge-on spiral galaxies
摘要：
我们分析了在{ \em Spitzer/IRAC} 4.5微米波段观测到的附近边缘螺旋星系的翘曲。在我们的24个星系样本中，我们发现了14个星系存在翘曲的证据。我们估计观测到的开始半径的翘曲在一个子样本的10个星系。利用从观测到的光分布和观测到的自转曲线导出的质量分布，计算了这些星系中的暗物质分布。然后，通过应用自洽的线性响应理论，在文献中获得的6个星系的旋转曲线的质量模型的理论预测的翘曲的起始半径。通过比较观测到的起始半径的理论，我们发现，具有恒定厚度的光盘不能解释的意见，适度张开盘是必要的。所需的扩口与观察结果一致。我们的分析表明，在我们的星系样本中，翘曲的开始是不对称的。我们定义了一个新的数量称为发作不对称指数，并研究其对星系属性的依赖。在具有较小盘尺度长度的星系中，翘曲的起始不对称性往往较大。我们还定义和量化的恒星光分布的全球不对称性，我们称之为边对星系的边对不对称性。它表明，在大多数情况下，在翘曲的发病不对称性，实际上是反相关的测量边缘上的不对称性，在我们的样本的边缘上的星系，这可能是合理的，表明周围的暗物质分布是不对称的。
英文摘要：
We analyze warps in the nearby edge-on spiral galaxies observed in the {\em Spitzer/IRAC} 4.5 micron band. In our sample of 24 galaxies we find evidence of warp in 14 galaxies. We estimate the observed onset radii for the warps in a subsample of 10 galaxies. The dark matter distribution in each of these galaxies are calculated using the mass distribution derived from the observed light distribution and the observed rotation curves. The theoretical predictions of the onset radii for the warps are then derived by applying a self-consistent linear response theory to the obtained mass models for 6 galaxies with rotation curves in the literature. By comparing the observed onset radii to the theoretical ones, we find that discs with constant thickness can not explain the observations; moderately flaring discs are needed. The required flaring is consistent with the observations. Our analysis shows that the onset of warp is not symmetric in our sample of galaxies. We define a new quantity called the onset-asymmetry index and study its dependence on galaxy properties. The onset asymmetries in warps tend to be larger in galaxies with smaller disc scale lengths. We also define and quantify the global asymmetry in the stellar light distribution, that we call the edge-on asymmetry in edge-on galaxies. It is shown that in most cases the onset asymmetry in warp is actually anti-correlated with the measured edge-on asymmetry in our sample of edge-on galaxies and this could plausibly indicate that the surrounding dark matter distribution is asymmetric.
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