Dissecting the size evolution of elliptical galaxies since z∼ 1: puffing-up versus minor-merging scenarios
Dissecting the size evolution of elliptical galaxies since z∼ 1: puffing-up versus minor-merging scenarios
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DOI：
10.1111/j.1365-2966.2011.19017.x
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发表时间：
2011-02
影响因子：
4.8
通讯作者：
I. Trujillo;I. Ferreras;I. G. D. L. Rosa
中科院分区：
文献类型：
--
作者：
I. Trujillo;I. Ferreras;I. G. D. L. Rosa
在一个固定的恒星质量，低红移早型星系的大小被发现是一个因素的2比他们的同行在z 1，星系形成模型的重要影响的结果。在本文中，我们探讨了建立的本地质量大小关系的椭圆星系使用两个视觉分类的样本。在低红移，我们从斯隆数字巡天中收集了2656个椭圆星系的子样本，而在更高的红移（高达z = 1），我们从哈勃太空望远镜/高级相机中提取了228个物体的样本。我们研究中的所有星系都有光谱数据，使我们能够确定恒星成分的年龄和质量。与文献中先前的说法相反，使用我们当地样本的恒星种群中包含的化石记录信息，我们没有发现任何证据表明在给定的恒星质量下存在年龄分离，这取决于星系的大小。在一个固定的动力学质量下，我们样本中两个极端年龄的四分位数之间的大小差异只有0.9%。因此，当地的证据并不支持这样一种假设，即现今的质量-大小关系是通过自下而上的序列逐步建立的，其中较老的星系占据了这个关系的较低部分，自形成以来一直保持不变。我们也没有在我们的高z样本中发现任何年龄隔离差异。因此，我们发现了一个大小的趋势，是不敏感的恒星人口的年龄，至少从z 1。这一结果支持了恒星质量-大小关系形成于z = 1的观点，所有星系都分布在一个大约相当于现在大小分布的1/2的区域。我们已经探讨了两种可能的规模增长方案：膨胀或小规模合并。事实上，大小的演变是独立的恒星的年龄，加上没有增加的关系与红移的散射不支持的膨胀机制。然而，观测证据在现阶段不能否定小合并假说。我们已经作出了一个估计的小合并事件的数量，使高Z星系的本地关系与所观察到的大小演变兼容。由于z= 0.8，如果合并的质量比是1：3，那么我们估计有103 ± 1次小合并，如果质量比是1：10，那么我们得到108 ± 2次合并。
At a fixed stellar mass, the size of low-redshift early-type galaxies is found to be a factor of 2 larger than that of their counterparts at z∼ 1, a result with important implications for galaxy formation models. In this paper, we have explored the buildup of the local mass–size relation of elliptical galaxies using two visually classified samples. At low redshift, we compiled a subsample of 2656 elliptical galaxies from the Sloan Digital Sky Survey, whereas at higher redshift (up to z∼ 1), we extracted a sample of 228 objects from the Hubble Space Telescope/Advanced Camera for Surveys images of the Great Observatories Origins Deep Survey. All the galaxies in our study have spectroscopic data, allowing us to determine the age and mass of the stellar component. Contrary to previous claims in the literature, using the fossil record information contained in the stellar populations of our local sample, we do not find any evidence for an age segregation at a given stellar mass, depending on the size of the galaxies. At a fixed dynamical mass, there is only a ≲9 per cent size difference in the two extreme age quartiles of our sample. Consequently, the local evidence does not support a scenario whereby the present-day mass–size relation has been progressively established via a bottom-up sequence, where older galaxies occupy the lower part of this relation, remaining in place since their formation. We do not find any age-segregation difference in our high-z sample either. Therefore, we find a trend in size that is insensitive to the age of the stellar populations, at least since z∼ 1. This result supports the idea that the stellar mass–size relation is formed at z∼ 1, with all galaxies populating a region which roughly corresponds to 1/2 of the present size distribution. We have explored two possible scenarios for size growth: puffing up or minor merging. The fact that the evolution in size is independent of the stellar age, together with the absence of an increase in the scatter of the relationship with redshift does not support the puffing-up mechanism. The observational evidence, however, cannot reject at this stage the minor-merging hypothesis. We have made an estimation of the number of minor-merger events necessary to bring the high-z galaxies into the local relation compatible with the observed size evolution. Since z= 0.8, if the mass ratio of the merger is 1:3, then we estimate ∼3 ± 1 minor mergers and if the ratio is 1:10, then we obtain ∼8 ± 2 events.