The G Dwarf Problem Exists in Other Galaxies
The G Dwarf Problem Exists in Other Galaxies
复制标题
其他星系中也存在G矮星问题
DOI：
10.1086/118068
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发表时间：
1996
期刊：
影响因子：
--
通讯作者：
L. Jones
中科院分区：
文献类型：
--
作者：
G. Worthey;B. Dorman;L. Jones
由化学演化的解析简单模型确定的丰度分布的恒星种群模型在三个方面不能与凸起主导星系的核心观测相匹配。首先，中紫外波段2000 < lam < 2400的光谱能量分布超出观测值约0.6等，其中大部分是由于金属贫乏的主序星造成的。其次，这些模型不能再现主要来自红巨星的金属敏感光学吸收特征。第三，对热星敏感的Ca II指数的强度与预测的a型水平分支星的数量不一致。星系中缺乏金属的恒星的数量至少比简单模型预测的少了两倍，这与太阳圆柱中的“G矮星问题”完全相似。在更大半径的局部星系群中进行的观测表明，金属贫乏恒星的缺乏适用于全球，而不仅仅是在核心中。由于富含金属的恒星占主导地位，原始星系在其恒星形成历史的早期将有充足的尘埃供应，因此可能会有微弱的莱曼- α发射，正如明显观察到的那样。我们证实，早期型星系不可能完全由小的全恒星子系统合并形成，这一结果已经通过动力学模拟得到了证实。峰值丰度分布的限制将限制未来的化学演化模型。它还将使早期星系和凸起的恒星群的年龄估计更加可靠。
Stellar population models with abundance distributions determined from the analytic Simple model of chemical evolution fail to match observations of the nuclei of bulge-dominated galaxies in three respects. First, the spectral energy distribution in the mid-ultraviolet range 2000 < lam < 2400 exceeds observation by ~ 0.6 mag. Most of that excess is due to metal-poor main sequence stars. Second, the models do not reproduce metal-sensitive optical absorption features that arise mainly from red giant stars. Third, the strength of a Ca II index sensitive to hot stars does not jibe with the predicted number of A-type horizontal branch stars. The number of metal poor stars in galaxies is at least a factor of two less than predicted by the Simple model, exactly similar to the ``G Dwarf problem'' in the solar cylinder. Observations at larger radii in local group galaxies indicate that the paucity of metal poor stars applies globally, rather than only in the nuclei. Because of the dominance of metal rich stars, primordial galaxies will have a plentiful dust supply early in their star formation history, and thus will probably have weak Lyman-alpha emission, as is apparently observed. We confirm that early-type galaxies cannot have been formed exclusively from mergers of small all-stellar subsystems, a result already established by dynamical simulations. The constraint of peaked abundance distributions will limit future chemical evolution models. It will also make age estimates for the stellar populations in early type galaxies and bulges more secure.