SECULAR EVOLUTION IN DISK GALAXIES: THE GROWTH OF PSEUDOBULGES AND PROBLEMS FOR COLD DARK MATTER GALAXY FORMATION
SECULAR EVOLUTION IN DISK GALAXIES: THE GROWTH OF PSEUDOBULGES AND PROBLEMS FOR COLD DARK MATTER GALAXY FORMATION
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发表时间：
2005-07
影响因子：
1
通讯作者：
J. Kormendy;D. Fisher
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作者：
J. Kormendy;D. Fisher
我们回顾了星系盘的内部长期演化{孤立盘演化的基本过程。我们专注于密集的中心特征的形成，这些特征看起来像经典的合并形成的凸起，但它们是由盘状气体缓慢形成的。我们称之为假凸起。作为存在性证明，我们回顾了棒是如何将圆盘气体重新排列成外环、内环和倾倒到中心的气体的。在模拟中，这种气体达到了很高的密度，在观测中，许多SB星系和椭圆形星系显示出中心气体的浓度。相关的恒星形成速率意味着假凸起的生长时间可能长达几十亿年。如果长期过程形成了伪装成凸起的密集中心，我们能将它们与合并形成的凸起区分开吗？观察表明，假凸起保留了对其磁盘起源的记忆。它们具有盘的一个或多个特征：(1)比经典的凸起形状更复杂，(2)有序速度与随机速度的比值更大，(3)速度色散更小，(4)核棒或螺旋结构，(5)从侧面看时呈方形结构，(6)接近指数级的亮度变化，以及(7)星暴。这些特征优先出现在棒状和椭圆形星系中，在这些星系中，长期演化应该是迅速的。所以最干净的假凸起的例子是可以辨认的。因此，观测和理论为星系演化的新图景做出了贡献，补充了分层聚类和合并。然而，冷暗物质星系形成的一个重要问题变得更加尖锐。在没有合并形成的凸起的证据的情况下，分层聚类是如何产生这么多纯盘状星系的？
We review internal secular evolution in galaxy disks { the fundamental process by which isolated disks evolve. We concentrate on the buildup of dense central features that look like classical, merger-built bulges but that were made slowly out of disk gas. We call these pseudobulges. As an existence proof, we review how bars rearrange disk gas into outer rings, inner rings, and gas dumped into the center. In simulations, this gas reaches high densities, and in the observations, many SB and oval galaxies show central concentrations of gas. Associated star formation rates imply plausible pseudobulge growth times of a few billion years. If secular processes built dense centers that masquerade as bulges, can we distinguish them from merger-built bulges? Observations show that pseudobulges retain a memory of their disky origin. They have one or more characteristics of disks: (1) atter shapes than those of classical bulges, (2) larger ratios of ordered to random velocities, (3) smaller velocity dispersions, (4) nuclear bars or spiral structure, (5) boxy structure when seen edge-on, (6) nearly exponential brightness proles, and (7) starbursts. These features occur preferentially in barred and oval galaxies in which secular evolution should be rapid. So the cleanest examples of pseudobulges are recognizable. Thus observations and theory contribute to a new picture of galaxy evolution that complements hierarchical clustering and merging. However, an important problem with cold dark matter galaxy formation gets more acute. How can hierarchical clustering produce so many pure disk galaxies with no evidence for merger-built bulges?