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arXiv 0907.3905astro-ph.CO
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环境在9个中等红移星系团星系形态转变中的作用

The role of environment in the morphological transformation of galaxies in 9 intermediate redshift clusters

M. Huertas-Company, G. Foex, G. Soucail, R. Pello

摘要:

我们分析了MegaCam在4个光度带(g,r,i,z)中观测到的9个0.4<z<0.6的大质量星系团的样本,从核心到半径为5 Mpc(~4000个星系)。星系团候选者是使用HyperZ计算的光度红移选择的。形态估计galSVM在两个广泛的形态类型(早期型和晚期型)。我们检查了红色序列和蓝云的形态组成,并通过质量有限样本(log(M/Msol)>9.5)中的形态-密度关系(T-Sigma)和形态-半径关系(T-R)来研究星系与其环境之间的关系。我们发现红色序列在z~0.5时已经存在,并且主要由质量非常大(log(M/Msol)>11.3)的早型星系组成。这些大质量星系似乎在进入星系团时就已经形成了,很可能是在下降的星系群中,因为这一比例与星系团半径保持不变。它们在集群中心的存在可以用反映早期组装历史的隔离效应来解释。因此,在星系团群体中发生的任何演化都发生在较低的质量(10.3<log(M/Msol)<11.3)。对于这些星系,演化,主要是由星系-星系相互作用的外围所揭示的T-Sigma关系。最后,大多数质量较小的星系(9.5<log(M/Msol)<10.3)在所有位置都是晚型星系,这表明它们还没有开始形态转变,即使这个低质量的仓可能受到不完整性的影响。

英文摘要:

[abridged] We analyze a sample of 9 massive clusters at 0.4<z<0.6 observed with MegaCam in 4 photometric bands (g,r,i,z) from the core to a radius of 5 Mpc (~4000 galaxies). Galaxy cluster candidates are selected using photometric redshifts computed with HyperZ. Morphologies are estimated with galSVM in two broad morphological types (early-type and late-type). We examine the morphological composition of the red-sequence and the blue-cloud and study the relations between galaxies and their environment through the morphology-density relations (T-Sigma) and the morphology-radius relation (T-R) in a mass limited sample (log(M/Msol)>9.5). We find that the red sequence is already in place at z~0.5 and it is mainly composed of very massive (log(M/Msol)>11.3) early-type galaxies. These massive galaxies seem to be already formed when they enter the cluster, probably in infalling groups, since the fraction remains constant with the cluster radius. Their presence in the cluster center could be explained by a segregation effect reflecting an early assembly history. Any evolution that takes place in the galaxy cluster population occurs therefore at lower masses (10.3<log(M/Msol)<11.3). For these galaxies, the evolution, is mainly driven by galaxy-galaxy interactions in the outskirts as revealed by the T-Sigma relation. Finally, the majority of less massive galaxies (9.5<log(M/Msol)<10.3) are late-type galaxies at all locations, suggesting that they have not started the morphological transformation yet even if this low mass bin might be affected by incompleteness.

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