椭圆星系的年龄和颜色-星等关系
The Age of Ellipticals and the Color-Magnitude Relation
摘要：
利用星系团中早型星系新的窄带色观测，我们重建了色-星等关系（CMR），其精度比以前的工作更高。然后，我们使用光谱确定的年龄和金属丰度从三个样本（Trager等人2008年，托马斯等人2005年，Gallazzi等人2006年），结合多金属丰度SED模型，比较预测的颜色与年轻的年龄（小于8 Gyr）与已知的CMR星系。我们发现，CMR不能复制的光谱测定的年龄和金属丰度的任何样品，尽管高的内部精度的光谱指数。相比之下，仅使用$<$ Fe $>$指数来确定[Fe/H]，并假设星系的恒星星族的平均年龄为12 Gyr，我们得到的颜色不仅与CMR的颜色零点完全匹配，而且与其斜率完全匹配。我们认为年轻的年龄估计，H $β$指数的来源，并检查红色连续色和大的H $β$值在星系光谱之间的冲突。我们的结论是，我们目前的恒星星族的理解是不足以正确解释H $β$值，我们的星系观测的总和支持一个古老的和单一的星系形成的情况。这一结果对所有使用H $β$指数来计算星系年龄的研究都有毁灭性的影响，因为使用H $β$与MgFe图将导致错误地推断年轻的年龄。
英文摘要：
Using new narrowband color observations of early-type galaxies in clusters, we reconstruct the color-magnitude relation (CMR) with a higher degree of accuracy than previous work. We then use the spectroscopically determined ages and metallicities from three samples (Trager et al 2008, Thomas et al 2005, Gallazzi et al 2006), combined with multi-metallicity SED models, to compare predicted colors for galaxies with young ages (less than 8 Gyr) with the known CMR. We find that the CMR cannot by reproduced by the spectroscopically determined ages and metallicities in any of the samples despite the high internal accuracies to the spectroscopic indices. In contrast, using only the $<$Fe$>$ index to determine [Fe/H], and assuming a mean age of 12 Gyr for a galaxy's stellar population, we derive colors that exactly match not only the color zeropoint of the CMR but also its slope. We consider the source of young age estimates, the H$β$ index, and examine the conflict between red continuum colors and large H$β$ values in galaxy spectra. We conclude that our current understanding of stellar populations is insufficient to correctly interpret H$β$ values and that the sum of our galaxy observations supports an old and monolithic scenario of galaxy formation. This result has a devastating impact on every study that has used the H$β$ index to calculate galaxy age, as the use of the H$β$ versus MgFe diagram will result in incorrectly deduced young ages.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
