Critical take on "Mass models of disk galaxies from the DiskMass Survey in MOND"
Critical take on "Mass models of disk galaxies from the DiskMass Survey in MOND"
复制标题
对“MOND 盘质量巡天中的盘星系质量模型”的批判性看法
DOI：
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发表时间：
2015
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影响因子：
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通讯作者：
M. Milgrom
中科院分区：
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作者：
M. Milgrom
安格斯等人。 （2015）最近对 MOND 提出了如下错误：通过研究 DiskMass 巡天中的 30 个盘状星系，他们得出了 MOND 预测的垂直于盘的速度色散剖面 $sigma_M(r)$，并将其与作为 DiskMass 项目一部分测量的 $sigma(r)$ 进行比较。这是MOND的一个新检验，与旋转曲线分析不同。 MOND 的一项非凡成就——Angus 等人没有讨论过。 -- $sigma_M$ 和 $sigma$ 的形状非常一致，即 $eta(r)equivsigma_M(r)/sigma(r)$ 与 $r$ 无关非常一致（而 $sigma$ 和 $sigma_M$ 强烈依赖于 $r$）。 MOND 发现的错误是 $eta$ 系统地高于 1（平均约为 1.3）。我已向安格斯等人建议。问题可能出在 DiskMass 色散上，对于当前的目的来说，它可能太低了：基于人口综合线剖面，它们可能会被较年轻的人口所过度重视，已知这些人口的色散和尺度高度比较老的人口小得多，而较老的人口对光分布的权重更大。我讨论了支持这一观点的独立证据，并表明，如果 DiskMas 离散度平均仅被低估 25%，MOND 预测在形状和幅度上与数据完全一致。现在，阿尼扬等人。 (2015) 在同样的基础上对 DiskMass $sigma$ 提出了质疑。他们针对银河系中的太阳柱表明：“将年轻+年老盘群的（单一）测量速度色散与老年盘群估计的尺度高度相结合，会低估盘面密度 $sim 2.$” 如果在银河系中发现的这种不匹配是典型的，对其进行校正将使测量的 DiskMass $sigma(r)$ 与预测的 MOND $sigma_M(r)$ 非常一致。
Angus et al. (2015) have recently faulted MOND as follows: Studying thirty disc galaxies from the DiskMass survey, they derive the profiles of velocity dispersion perpendicular to the discs as predicted by MOND, $sigma_M(r)$, and compare them with $sigma(r)$, measured as part of the DiskMass project. This is a new test of MOND, different from rotation-curve analysis. A nontrivial accomplishment of MOND -- not discussed by Angus et al. -- is that the shapes of $sigma_M$ and $sigma$ agree very well, i.e, $eta(r)equivsigma_M(r)/sigma(r)$ is well consistent with being $r$-independent (while $sigma$ and $sigma_M$ are strongly $r$ dependent). The fault found with MOND was that $eta$ is systematically above 1 (with an average of about 1.3). I have suggested to Angus et al. that the fault may lie with the DiskMass dispersions, which may well be too low for the purpose at hand: Being based on population-integrated line profiles, they may be overweighed by younger populations, known to have much smaller dispersions, and scale heights, than the older populations, which weigh more heavily on the light distributions. I discuss independent evidence that supports this view, and show, besides, that if the DiskMas dispersions are underestimates by only 25 %, on average, the MOND predictions are in full agreement with the data, in shape and magnitude. Now, Aniyan et al. (2015) have questioned the DiskMass $sigma$ on the same basis. They show for the solar column in the Milky Way that: " Combining the (single) measured velocity dispersion of the total young + old disc population... with the scale height estimated for the older population would underestimate the disc surface density by a factor of $sim 2.$" If this mismatch found for the Milky Way is typical, correcting for it would bring the measured DiskMass $sigma(r)$ to a remarkable agreement with the predicted MOND $sigma_M(r)$.