Confirmation of Enhanced Dwarf-sensitive Absorption Features in the Spectra of Massive Elliptical Galaxies: Further Evidence for a Non-universal Initial Mass Function
We recently found that massive cluster elliptical galaxies have strong Na I 8183,8195 and FeH 9916 Wing-Ford band absorption, indicating the presence of a very large population of stars with masses <~ 0.3 M_sun. Here we test this result by comparing the elliptical galaxy spectra to those of luminous globular clusters associated with M31. These globular clusters have similar metallicities, abundance ratios and ages as massive elliptical galaxies but their low dynamical mass-to-light ratios rule out steep stellar initial mass functions (IMFs). From high quality Keck spectra we find that the dwarf-sensitive absorption lines in globular clusters are significantly weaker than in elliptical galaxies, and consistent with normal IMFs. The differences in the Na I and Wing-Ford indices are 0.027 +- 0.007 mag and 0.017 +- 0.006 mag respectively. We directly compare the two classes of objects by subtracting the averaged globular cluster spectrum from the averaged elliptical galaxy spectrum. The difference spectrum is well fit by the difference between a stellar population synthesis model with a bottom-heavy IMF and one with a bottom-light IMF. We speculate that the slope of the IMF may vary with velocity dispersion, although it is not yet clear what physical mechanism would be responsible for such a relation.
Metallicity Gradients - Mass Dependency in Dwarf Elliptical Galaxies
星系的形成和演化是由它们的恒星星族径向梯度决定的。最近的两篇文章提出了相互矛盾的结果，关于早期型矮星系的金属丰度梯度的质量依赖性。一方面，Spolaor等人表明总金属丰度、Z/H和质量之间存在紧密的正相关关系。另一方面，在不同的样品中，我们没有发现任何涉及Fe/H的趋势（Koleva等人）。为了调查的差异的起源，我们检查各种因素，可能会影响确定的梯度：即天空减法和信噪比。我们的结论是，我们的梯度检测远高于可能的分析偏差。然后，我们测量了Mg/Fe相对丰度分布，发现了中等梯度。导出的Z/H梯度分散在-0.4dex/re附近。这两个样本包含相同类型的对象，并且仍然不理解不一致的原因。根据ESO望远镜在La Silla Paranal天文台根据ID076.B-0196计划进行的观测。
Kinematic Confirmation of a Remarkable Linear Trail of Galaxies in the NGC 1052 Field, Consistent with Formation in a High-Speed Bullet Dwarf Collision
Yale University（耶鲁大学）；Princeton University（普林斯顿大学）；University of Toronto（多伦多大学）；San Jose State University（圣何塞州立大学）；University of California Santa Cruz（加州大学圣克鲁兹分校）
Keck/LRIS Spectroscopic Confirmation of Coma Cluster Dwarf Galaxy Membership Assignments
Keck/LRIS多目标光谱仪对后发座星系团核心区的140个最低和最高表面亮度的暗（19 < R < 22）矮星系候选者进行了测量。这些光谱被用来测量红移，并建立这些微弱的矮种群的成员资格。低表面亮度样本的主要目标是测试我们使用形态和表面亮度标准区分后发座星系团成员和背景星系的能力，使用高分辨率HST/ACS图像。候选人被评为预期成员，不确定，或预期的背景。从93个光谱中识别出51个矮星系成员和20个背景星系。我们的形态成员估计成功率为100%的对象，预计将成为成员和优于90%的星系预计将在背景中。我们确认，低表面亮度是一个很好的指标集群成员。高表面亮度星系几乎总是背景与混乱所产生的情况下，只有罕见的紧凑的椭圆星系。在中等表面亮度下出现更多问题的情况。这些星系中的许多都被赋予了不确定的成员评级，并且这些星系被发现是成员的时间约为一半。包括颜色信息将改进成员资格确定，但是对于在仅使用表面亮度和形态标准时已经被错误识别的一些相同对象将失败。具有B-V色的紧凑椭圆星系，特别是红色序列红向0.2等，需要光谱跟踪。在47个高表面亮度的样本中，有19个物体的红移使它们位于后发座星系团中。红移测量和使用间接手段建立集群成员进行了讨论。
Stellar Population Properties of Ultracompact Dwarfs in M87: a Mass-metallicity Correlation Connecting Low-metallicity Globular Clusters and Compact Ellipticals
