标题： z~1早型星系中多重恒星种群的光谱检测 显示英文标题

标题： Spectral detection of multiple stellar populations in z~1 early-type galaxies

摘要： 我们基于在4000A静止框架区域的两个主要与年龄相关的光度指数H+K(CaII)和Delta4000的测量，对一个15个早型星系(ETGs)的样本进行了光谱分析，这些星系位于0.7 < z_{规范} < 1.1范围内，并在GOODS-South区域中通过形态选择得到。通过将这两个不同的指数与恒星形成合成模型进行比较得出的年龄，至少对于九个星系（占样本的60%）彼此不一致，而对于其余六个星系，从整体光谱能量分布（SED）拟合得出的年龄与从两个指数得出的年龄也不一致。因此，我们假设许多星系的恒星组成包含两个年龄不同的恒星成分。考虑到指数值和观测到的SED进行的双成分分析，完全解释了观测数据，并在15个物体中的9个中改善了标准单成分SED拟合的结果，即那些两个指数指向不同年龄的物体。在所有这些物体中，大部分质量属于较为演化的恒星，而一小部分质量则年轻许多吉年。在某些情况下，由于H+K(CaII)指数的敏感性，我们发现较次要的年轻成分显示出近期恒星形成的迹象。年轻恒星成分的年龄分布似乎在时间上是均匀的，这表明在高红移ETGs的演化过程中，少量的恒星形成可能是常见的。我们认为这些新的恒星形成事件可能经常由内部原因触发，这是由于存在少量气体储备。 显示英文摘要

摘要： We present a spectroscopic analysis based on measurements of two mainly age-dependent spectrophotometric indices in the 4000A rest frame region, i.e. H+K(CaII) and Delta4000, for a sample of 15 early-type galaxies (ETGs) at 0.7 < z_{spec} < 1.1, morphologically selected in the GOODS-South field. Ages derived from the two different indices by means of the comparison with stellar population synthesis models, are not consistent with each other for at least nine galaxies (60 per cent of the sample), while for the remaining six galaxies, the ages derived from their global spectral energy distribution (SED) fitting are not consistent with those derived from the two indices. We then hypothesized that the stellar content of many galaxies is made of two stellar components with different ages. The double-component analysis, performed by taking into account both the index values and the observed SED, fully explains the observational data and improves the results of the standard one-component SED fitting in 9 out of the 15 objects, i.e. those for which the two indices point towards two different ages. In all of them, the bulk of the mass belongs to rather evolved stars, while a small mass fraction is many Gyr younger. In some cases, thanks to the sensitivity of the H+K(CaII) index, we find that the minor younger component reveals signs of recent star formation. The distribution of the ages of the younger stellar components appears uniformly in time and this suggests that small amounts of star formation could be common during the evolution of high-z ETGs. We argue the possibility that these new star formation episodes could be frequently triggered by internal causes due to the presence of small gas reservoir.