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arXiv 1003.2631astro-ph.CO
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MACS \,J0025中一个主要的星系团合并对星系演化的影响。4 -1225

The impact of a major cluster merger on galaxy evolution in MACS\,J0025.4-1225

C. -J. Ma, H. Ebeling, P. Marshall, T. Schrabback

摘要:

我们提出了一个广泛的形态学,光谱学和光度学的研究结果的星系人口的MACS J0025.4 $-$ 1225(z=0.586),一个主要的集群合并与明确的分离的黑暗和明亮的物质,检查合并对星系演化的影响。根据Keck DEIMOS获得的436个星系光谱,在距星系团中心4 Mpc的范围内共识别出212个星系团成员,并将它们分为三种光谱类型:111条吸收线,90条发射线(包括23条e(a)和11条e(b)),6个E+A星系。吸收(发射)线星系的比例是一个单调增加(减少)函数的投影星系密度和径向距离的集群中心。更重要的是,观测到的6个E+A星系团成员都位于星系团的暗物质峰之间,X射线通量峰的半径约为0.3Mpc,而不像其他中红移星系团中的E+A星系通常会避开核心区域。此外,我们使用哈伯太空望远镜的影像,根据星系团成员的形态类型进行分类。我们发现MACS J 0025中螺旋星系和透镜状星系的全球比例是迄今为止在z>0.5的星系团中观测到的最高比例之一。所观察到的E+A星系被发现是透镜型的Sersic指数为~2,提高了暗物质峰之间的本地分数的S 0到70%。结合我们对星系群空间分布、形态和光谱特征的分析结果,我们认为这些E+A型星系的星爆阶段都是在0.5- 1Gyr前的第一次核心穿越中开始和结束的,并且它们的形态已经由于星系团核心附近的冲压压力和/或潮汐力而转变为S 0。相比之下,正在进行的恒星爆发主要是在下落星系中观察到的,因此似乎与星系团合并无关。

英文摘要:

We present results of an extensive morphological, spectroscopic, and photometric study of the galaxy population of MACS J0025.4$-$1225 (z=0.586), a major cluster merger with clear segregation of dark and luminous matter, to examine the impact of mergers on galaxy evolution. Based on 436 galaxy spectra obtained with Keck DEIMOS, we identified 212 cluster members within 4 Mpc of the cluster centre, and classified them using three spectroscopic types; we find 111 absorption-line, 90 emission-line (including 23 e(a) and 11 e(b)), and 6 E+A galaxies. The fraction of absorption(emission)-line galaxies is a monotonically increasing(decreasing) function of both projected galaxy density and radial distance to the cluster center. More importantly, the 6 observed E+A cluster members are all located between the dark-matter peaks of the cluster and within ~0.3Mpc radius of the X-ray flux peak, unlike the E+A galaxies in other intermediate-redshift clusters which are usually found to avoid the core region. In addition, we use Hubble Space Telescope imaging to classify cluster members according to morphological type. We find the global fraction of spiral and lenticular galaxies in MACS J0025 to be among the highest observed to date in clusters at z>0.5. The observed E+A galaxies are found to be of lenticular type with Sersic indices of ~2, boosting the local fraction of S0 to 70 per cent between the dark-matter peaks. Combing the results of our analysis of the spatial distribution, morphology, and spectroscopic features of the galaxy population, we propose that the starburst phase of these E+A galaxies was both initiated and terminated during the first core-passage about 0.5--1Gyr ago, and that their morphology has already been transformed into S0 due to ram pressure and/or tidal forces near the cluster core. By contrast, ongoing starbursts are observed predominantly in infalling galaxies, and thus appears to be unrelated to the cluster merger.

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