The SAURON project - IX. A kinematic classification for early-type galaxies
The SAURON project - IX. A kinematic classification for early-type galaxies
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DOI：
10.1111/j.1365-2966.2007.11752.x
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发表时间：
2007-08-01
影响因子：
4.8
通讯作者：
Sarzi, Marc
中科院分区：
文献类型：
--
作者：
Emsellem, Eric;Cappellari, Michele;Sarzi, Marc
使用 SAURON 积分场摄谱仪获得的 48 个代表性椭圆形 (E) 和透镜状 (S0) 星系的二维恒星运动学表明，早期型星系以两种广泛的形式出现，具体取决于它们是否表现出明显的大尺度旋转。我们定义了一个新参数 lambda(R)，相当于 < R 垂直条 V 垂直条 >/< R 根 V(2)+sigma(2)>，它涉及整个二维运动场上的光度加权平均值作为代理，以量化观测到的每单位质量的投影恒星角动量。我们用它作为新运动学分类的基础：早期型星系被分为慢速和快速旋转体，具体取决于它们的有效半径 R(e) 内的 lambda(R) 值是否分别低于或高于 0.1。慢速和快速旋转体被证明是物理上不同的星系类别，这一结果不能简单地是视角偏差的结果。快速自转星系往往是光度相对较低的星系，M(B) 大于或接近 20.5。慢速旋转星系往往是更亮、质量更大的星系，但其绝对星等分布范围仍然很广。我们样本中的三个慢速旋转体（其中最大的旋转体）与零旋转一致。值得注意的是，所有其他慢速旋转器（除了 NGC 4550 的非典型情况）都包含一个大型 kpc 规模的运动解耦核心 (KDC)。所有快速旋转体（除了一个具有众所周知的不规则壳层的星系）都显示出良好对齐的光度和运动轴以及较小的速度扭曲，而大多数慢速旋转体则表现出显着的未对准和速度扭曲。这些结果得到了索伦观测到的另外 18 个早期型星系的补充的支持。在另一篇配套论文（论文 X）中，我们还表明，快旋转体和慢旋转体在轨道分布方面是不同的类别。我们认为气体是快速自转体形成和演化的关键成分，而最慢自转体是在引力势井深处达到的极端演化终点，其中无耗散合并在演化中起主要作用，并且大部分重子角动量被向外排出。需要在宇宙学背景下进行详细的数值模拟，以了解如何在慢速旋转体中形成大规模 KDC，并且更普遍地解释早期型星系中 lambda(R) 值的分布以及快慢旋转体之间的区别。
Two-dimensional stellar kinematics of 48 representative elliptical (E) and lenticular (S0) galaxies obtained with the SAURON integral-field spectrograph reveal that early-type galaxies appear in two broad flavours, depending on whether they exhibit clear large-scale rotation or not. We define a new parameter lambda(R) equivalent to < R vertical bar V vertical bar >/< R root V(2)+sigma(2)>, which involves luminosity-weighted averages over the full two-dimensional kinematic field as a proxy to quantify the observed projected stellar angular momentum per unit mass. We use it as a basis for a new kinematic classification: early-type galaxies are separated into slow and fast rotators, depending on whether they have lambda(R) values within their effective radius R(e) below or above 0.1, respectively. Slow and fast rotators are shown to be physically distinct classes of galaxies, a result which cannot simply be the consequence of a biased viewing angle. Fast rotators tend to be relatively low-luminosity galaxies with M(B) greater than or similar to-20.5. Slow rotators tend to be brighter and more massive galaxies, but are still spread over a wide range of absolute magnitude. Three slow rotators of our sample, among the most massive ones, are consistent with zero rotation. Remarkably, all other slow rotators (besides the atypical case of NGC 4550) contain a large kpc-scale kinematically decoupled core (KDC). All fast rotators (except one galaxy with well-known irregular shells) show well-aligned photometric and kinemetric axes, and small velocity twists, in contrast with most slow rotators which exhibit significant misalignments and velocity twists. These results are supported by a supplement of 18 additional early-type galaxies observed with SAURON. In a companion paper (Paper X), we also show that fast and slow rotators are distinct classes in terms of their orbital distribution. We suggest that gas is a key ingredient in the formation and evolution of fast rotators, and that the slowest rotators are the extreme evolutionary end point reached deep in gravitational potential wells where dissipationless mergers had a major role in the evolution, and for which most of the baryonic angular momentum was expelled outwards. Detailed numerical simulations in a cosmological context are required to understand how to form large-scale KDCs within slow rotators, and more generally to explain the distribution of lambda(R) values within early-type galaxies and the distinction between fast and slow rotators.