Age Determination of Elliptical Galaxies using H γ Profile

这项研究旨在通过测量椭圆星系的光谱年龄来揭示它们的形成时代。我们用Subaru(NAOJ)、WTT(西班牙、英国)和NTT(ESO)望远镜拍摄了27个极高质量的椭圆星系(场内和星系团中的13个，室女星系团中的14个)的光谱，并用我们自己发展的汞剖面方法测量了它们的年龄和化学丰度。汞剖面方法是解开星系光谱中年龄和金属丰度效应的一种非常有效的方法，自从Vazdekis和Arimoto(1999)提出以来，受到了广泛的重视。这项研究是第一次将汞剖面法应用于数量可观的星系样本。在这项研究中，我们已经弄清楚了椭圆星系的年龄和金属度是如何依赖于星系质量、光度和环境的。还研究了银河系内年龄和金属丰度的空间分布。我们的结果…更多的LTS表明：1)星系团环境中的大质量椭圆星系是均匀老的(&lt；10个回旋)，而在野外的大质量椭圆星系则表现出从6个回转到10个回旋年龄的散射。这表明，直到最近，一些带场的椭圆体才经历了长时间的恒星形成。2)矮小椭圆星系在其年龄上表现出广泛的散射，从3个回转到10个回转，与它们所在的位置无关。这表明恒星形成的历史与之前所认为的相反，相当复杂。3)椭圆星系的镁铁比与星系质量有很强的相关性，即质量越大的星系，其镁/铁比越小，说明质量越大的椭圆星系的恒星形成周期越短。4)在一个矮小的椭圆M32星系(M31螺旋星系的伴星系)中，恒星年龄向星系中心方向递减，镁铁比也向星系中心递减。这是一个强有力的证据，表明星系中心可能由于耗散气体的流入而形成了长期的恒星。综上所述，尽管椭圆星系的形成确实表现出广泛的多样性(特别是在矮小椭圆形星系中)，但更多的大质量星系是在致密星系团环境中更早形成的。较少

This research aimed to reveal the formation epoch of elliptical galaxies by measuring their spectroscopic ages. We have taken spectra of 27 elliptical galaxies (13 in the field and group of galaxies and 14 in the Virgo cluster of galaxies) of extremely high quality with Subaru (NAOJ), WTT(Spain, UK) and NTT(ESO) telescopes and have measured their ages and chemical abundances by using the Hg profile method, which we have developed by ourselves. The Hg profile method is a quite efficient approach to disentangle age and metallicity effects in galaxy spectra and has been appreciated a lot since it was proposed by Vazdekis & Arimoto (1999). This study is the first one that applies the Hg profile method to a significantly large number of galaxy samples. In this study, we have made it clear how the ages and metallicities of elliptical galaxies depend on galaxy mass, luminosity, and the environment. The spatial distribution of age and metallicity within a galaxy has also been studied. Our resu … More lts show that 1)massive elliptical galaxies in cluster environment are uniformly old (<10 Gyrs), while those in the field show a scatter in ages spanning from 6 Gyrs to 10 Gyrs old. This indicates that some of filed ellipticals had experienced long lasting star formation until rather recently. 2)Dwarf elliptical galaxies show wide scatter in their ages, from 3 Gyrs to 10 Gyrs old, independent of where they locate. This suggests a rather complicated history of star formation in contrast to what has been thought previously. 3)Mg/Fe ratio of elliptical galaxies shows strong correlation with galaxy mass,; ie., moremassive galaxies tend to have smaller Mg/Fe ratio, suggesting shorter star formation period in more massive elliptical galaxies. 4) In a dwarf elliptical M32 (a companion galaxy of M31 spiral galaxy), the stellar age decreases towards galaxy centre and Mg/Fe ratio too. This is a strong evidence for a long lasting star formation at the galaxy center due to perhaps dissipative gas infall.In summary we could say that although it is true that formation of elliptical galaxies shows wide variety (in particular among dwarf ellipticals) more massive galaxies formed earlier in the dense cluster environment. Less