Messier 31的宽视场HI镶嵌图。II .盘的弯曲、旋转和暗物质晕
A wide-field HI mosaic of Messier 31. II.The disk warp, rotation and the dark matter halo
摘要：
我们测试宇宙学模型的结构形成使用最近的旋涡星系，M31，确定使用最近的深，全磁盘21厘米成像调查平滑到466 pc分辨率的旋转曲线。我们拟合了一个倾斜环模型的HI数据从8到37千秒差距。M31的圆盘从25 kpc向外弯曲，并且相对于我们的视线变得更加倾斜。没有暗物质晕的牛顿动力学提供了一个非常差的拟合使用翘曲模型得出的旋转曲线。然而，在修正的牛顿动力学框架下，21厘米旋转曲线很好地拟合由重子物质密度单独跟踪的引力势。包含一个暗物质晕的密度分布预测的结构形成的层次聚类LambdaCDM宇宙学的质量模型，在牛顿动力学兼容的旋转曲线数据。最佳拟合的暗晕浓度为C=12，其总质量为1.2 × 10^{12} Msun。如果考虑具有恒定密度核心的暗晕模型，核心半径必须大于20 kpc，以便模型拟合数据。我们外推最适合的LambdaCDM和恒定密度的核心质量模型非常大的银河中心半径，相当于暗物质晕的大小。在这样大的半径使用其他动力学示踪剂确定的M31质量的预测质量的比较，证实了我们的结果的有效性。特别是LambdaCDM暗晕模型，它最适合21厘米的数据以及再现的M31质量追溯到560千秒差距。我们估计M31的总质量为1.3 × 10^{12} Msun，重子分数为12%，只有6%的重子在中性气体中。
英文摘要：
We test cosmological models of structure formation using the rotation curve of the nearest spiral galaxy, M31, determined using a recent deep, full-disk 21-cm imaging survey smoothed to 466 pc resolution. We fit a tilted ring model to the HI data from 8 to 37 kpc. The disk of M31 warps from 25 kpc outwards and becomes more inclined with respect to our line of sight. Newtonian dynamics without a dark matter halo provide a very poor fit to the rotation curve derived using the warp model. In the framework of modified Newtonian dynamic however the 21-cm rotation curve is well fitted by the gravitational potential traced by the baryonic matter density alone. The inclusion of a dark matter halo with a density profile as predicted by structure formation in a hierarchical clustering LambdaCDM cosmology makes the mass model in newtonian dynamic compatible with the rotation curve data. The dark halo concentration for the best fit is C=12 and its total mass is 1.2 10^{12} Msun. If a dark halo model with a constant density core is considered, the core radius has to be larger than 20 kpc in order for the model to fit to the data. We extrapolate the best-fit LambdaCDM and constant-density core mass models to very large galactocentric radii, comparable to the size of the dark matter halo. A comparison of the predicted mass with the M31 mass determined at such large radii using other dynamical tracers, confirms the validity of our results. In particular the LambdaCDM dark halo model which best fits the 21-cm data well reproduces the M31 mass traced out to 560 kpc. Our estimated total mass of M31 is 1.3 10^{12} Msun, with 12% baryonic fraction and only 6% of the baryons in neutral gas.
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