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早型星系基面的结构

Structures in the fundamental plane of early-type galaxies

Didier Fraix-Burnet, Magali Dugué, Tanuka Chattopadhyay, Asis Kumar Chattopadhyay, Emmanuel Davoust

备注：
Accepted for publication in MNRAS; Monthly Notices of the Royal Astronomical Society (2010)
发表信息：
Monthly Notices of the Royal Astronomical Society 407, 4 (2010) 2207?2222
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摘要：

早型星系的基本面是一个相当紧密的三参数相关发现于20多年前。它已经抵制了全球和精确的物理解释，尽管随之而来的一些工作，观测，理论或使用数值模拟。看来它的精确性质取决于研究中的星系数量。而不是选择先验的这些人口，我们建议客观地构建同源的人口多变量分析。我们已经进行了多变量集群和支序分析的样本56个低红移星系团包含699个早型星系，使用四个参数：有效半径，速度色散，表面亮度平均有效半径，和Mg 2指数。我们所有的分析都与七个群体相一致，这些群体在全球基本面上定义了不同的区域，而不是在其厚度上。事实上，每一个群体都有自己的基本面，对于不太多样化的群体来说，基本面的定义更为宽松。我们的结论是，全球基本平面是不是一个弯曲的表面，但由几个组的集合特征的几个基本平面在参数空间中具有不同的厚度和方向。我们的多样化设想可能表明，多样化的程度与转变事件的数量和性质有关，基本面是几个转变事件的结果。我们还表明，我们的分类，而不是基本平面，是普遍的，在我们的红移范围内（0.007 - 0.053）。我们发现，这三组最薄的基本面大概形成通过耗散（湿）合并。在其中一个星系中，这种合并一定是相当古老的，因为它的星系金属含量相对较低，其中两个星系团随后经历了干合并，以增加它们的质量。在k-空间中，第三个明显占据了（透镜星系或螺旋星系的）凸起所在的区域，也可能是通过微小的合并和吸积形成的。最不多样化的两个组可能不是由主要合并形成的，并且一定受到相互作用的强烈影响，其中一个组的物体中的一些气体可能被清除了。基于我们这七个星系群的星系的特定集合历史的解释表明，它们确实是同源的。它们是直接从几个观测值中获得的，因此独立于任何先验分类。与这些群体相关的多样化情景并不依赖于模型或数值模拟，而是客观地由分支分析提供。因此，我们的分类更容易与模型和数值模拟相比，我们的工作可以很容易地重复额外的观测。

英文摘要：

The fundamental plane of early-type galaxies is a rather tight three-parameter correlation discovered more than twenty years ago. It has resisted a both global and precise physical interpretation despite a consequent number of works, observational, theoretical or using numerical simulations. It appears that its precise properties depend on the population of galaxies in study. Instead of selecting a priori these populations, we propose to objectively construct homologous populations from multivariate analyses. We have undertaken multivariate cluster and cladistic analyses of a sample of 56 low-redshift galaxy clusters containing 699 early-type galaxies, using four parameters: effective radius, velocity dispersion, surface brightness averaged over effective radius, and Mg2 index. All our analyses are consistent with seven groups that define separate regions on the global fundamental plane, not across its thickness. In fact, each group shows its own fundamental plane, which is more loosely defined for less diversified groups. We conclude that the global fundamental plane is not a bent surface, but made of a collection of several groups characterizing several fundamental planes with different thicknesses and orientations in the parameter space. Our diversification scenario probably indicates that the level of diversity is linked to the number and the nature of transforming events and that the fundamental plane is the result of several transforming events. We also show that our classification, not the fundamental planes, is universal within our redshift range (0.007 - 0.053). We find that the three groups with the thinnest fundamental planes presumably formed through dissipative (wet) mergers. In one of them, this(ese) merger(s) must have been quite ancient because of the relatively low metallicity of its galaxies, Two of these groups have subsequently undergone dry mergers to increase their masses. In the k-space, the third one clearly occupies the region where bulges (of lenticular or spiral galaxies) lie and might also have formed through minor mergers and accretions. The two least diversified groups probably did not form by major mergers and must have been strongly affected by interactions, some of the gas in the objects of one of these groups having possibly been swept out. The interpretation, based on specific assembly histories of galaxies of our seven groups, shows that they are truly homologous. They were obtained directly from several observables, thus independently of any a priori classification. The diversification scenario relating these groups does not depend on models or numerical simulations, but is objectively provided by the cladistic analysis. Consequently, our classification is more easily compared to models and numerical simulations, and our work can be readily repeated with additional observables.

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