Dark matter content and internal dynamics of NGC 4697 : NMAGIC particle models from slit data and planetary nebula velocities
Dark matter content and internal dynamics of NGC 4697 : NMAGIC particle models from slit data and planetary nebula velocities
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DOI：
10.1111/j.1365-2966.2008.12905.x
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发表时间：
2008-02
影响因子：
4.8
通讯作者：
F. Lorenzi;O. Gerhard;R. Saglia;N. Sambhus;V. Debattista;M. Pannella;R. G. M. Garching;Astron. Inst.;U. Basel;Centre for Astroph.;U. C. Lancashire;Ifa;U. Hawaii
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作者：
F. Lorenzi;O. Gerhard;R. Saglia;N. Sambhus;V. Debattista;M. Pannella;R. G. M. Garching;Astron. Inst.;U. Basel;Centre for Astroph.;U. C. Lancashire;Ifa;U. Hawaii
我们提出了 NGC 4697 的动力学研究，NGC 4697 是一个几乎边缘的、中等光度的 E4 椭圆星系，结合了新的表面亮度光度测量、新的和已发表的长缝吸收线运动学数据以及已发表的行星状星云 (PN) 速度数据。组合的运动学数据集延伸至 5 弧分 (4.5Re)，使我们能够探测星系的外晕。我们第一次使用新的、灵活的 χ 2 定制粒子代码 NMAGIC 对这样的数据集进行建模。我们扩展了 NMAGIC 以包括视见效应，引入了一种有效的方案来估计质光比，并结合了最大似然技术来解释离散速度测量。为了对 PN 运动学进行建模，我们使用在两个不同空间网格上计算的视线速度和速度离散度，并且我们还使用似然法的各个速度测量值，以确保我们的结果不会因我们处理 PN 测量值的方式而产生偏差。我们生成轴对称自洽模型以及包含各种暗物质晕的模型。这些模型拟合了所有平均速度和速度色散数据，χ 2 /N < 1，无论是在只有发光物质的情况下还是在可能包括相当大的光晕的情况下。似然分析与速度直方图表明，具有低密度晕的模型（5Re 处的圆周速度 vc � 200 km s -1）与数据不一致。 5Re 时 vc � 250 km s −1 的一系列大质量晕最适合 PN 数据。为了获得更强的结果，需要更大半径的 PN 速度。最佳拟合模型具有轻微的径向各向异性；各向异性参数在中心处为 β � 0.3，在半径 � 2Re 处增加到 β � 0.5。
We present a dynamical study of NGC 4697, an almost edge-on, intermediate-luminosity, E4 elliptical galaxy, combining new surface brightness photometry, new as well as published long-slit absorption-line kinematic data, and published planetary nebula (PN) velocity data. The combined kinematic data set extends out to � 5 arcmin (� 4.5Re) and allows us to probe the galaxy’s outer halo. For the first time, we model such a data set with the new and flexible χ 2 -made-to-measure particle code NMAGIC. We extend NMAGIC to include seeing effects, introduce an efficient scheme to estimate the mass-to-light ratio, and incorporate a maximum-likelihood technique to account for discrete velocity measurements. For modelling the PN kinematics, we use line-of-sight velocities and velocity dispersions computed on two different spatial grids, and we also use the individual velocity measurements with the likelihood method, in order to make sure that our results are not biased by the way we treat the PN measurements. We generate axisymmetric self-consistent models as well models including various dark matter haloes. These models fit all the mean velocity and velocity dispersion data with χ 2 /N < 1, both in the case with only luminous matter and in potentials including quite massive haloes. The likelihood analysis together with the velocity histograms suggest that models with low-density haloes such that the circular velocity vc � 200 km s −1 at 5Re are not consistent with the data. A range of massive haloes with vc � 250 km s −1 at 5Re fit the PN data best. To derive stronger results would require PN velocities at even larger radii. The best-fitting models are slightly radially anisotropic; the anisotropy parameter β � 0.3 at the centre, increasing to β � 0.5 at radii � 2Re.