An early phase of environmental effects on galaxy properties unveiled by near-infrared spectroscopy of protocluster galaxies at z > 2
An early phase of environmental effects on galaxy properties unveiled by near-infrared spectroscopy of protocluster galaxies at z > 2
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DOI：
10.1093/mnras/stv051
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发表时间：
2014-06
影响因子：
4.8
通讯作者：
R. Shimakawa;T. Kodama;K. Tadaki;M. Hayashi;Y. Koyama;I. Tanaka
中科院分区：
文献类型：
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作者：
R. Shimakawa;T. Kodama;K. Tadaki;M. Hayashi;Y. Koyama;I. Tanaka
利用Subaru望远镜上的多目标红外照相摄谱仪（MOIRCS）对两个富氢原星系团（PKS 1138-262，z=2.2; USS 1558-003，z = 2.5）中的窄带选择性Hα发射体（HAE）进行了近红外光谱研究。这些原星系团是当今所见最大质量星系团的祖先。z > 2处识别出的HAE显示出非常高的激发能级，其特征是比低z星系的[Oiii]/Hβ线比高得多。这样高的激发水平是由它们的高比星星形成率（sSFR）和较低的气体金属丰度定性驱动的。此外，我们调查的气体金属丰度的环境依赖性，通过比较的HAE在原星团与那些在一般领域在类似的红移。我们发现，在M范围内，在给定的恒星质量下，原星系团星系的气态金属丰度比场星系的气态金属丰度更富集。10 11 M⊙。这可以归因于许多过程，如内在（或自然）效应，外部（或培育）效应，和一些系统性的影响（抽样偏差）。内在（自然）效应包括星系演化的“缩小”高级阶段。另一方面，外部（滋养）效应包括由于星系际介质的压力较高而导致的化学富集气体的再循环或原星系团中储层中外部气体的剥离。虽然，没有一个解释是完美的，外部效应，如气体循环或剥离似乎是有利的。
This work presents the results from our near-infrared spectroscopy of narrow-band selected Hα emitters (HAEs) in two rich protoclusters (PKS 1138–262 at z=2.2 and USS 1558–003 at z = 2.5) with the Multi-Object Infrared Camera and Spectrograph (MOIRCS) on the Subaru telescope. These protoclusters are the ancestors of the most massive class of galaxy clusters seen today. The identified HAEs at z > 2 show very high excitation levels as characterized by much higher [Oiii]/Hβ line ratios than those of low-z galaxies. Such a high excitation level is qualitatively driven by their high specific star formation rates (sSFRs) and lower gaseous metallicities. Furthermore, we investigate the environmental dependence of gaseous metallicities by comparing the HAEs in the protoclustrers with those in the general field at similar redshifts. We find that the gaseous metallicities of protocluster galaxies are more chemically enriched than those of field galaxies at a given stellar mass in the range of M⋆ . 10 11 M⊙. This can be attributed to many processes, such as intrinsic (or nature) effects, external (or nurture) effects, and some systematic effects (sampling bias). The intrinsic (nature) effects include the advanced stage of “downsizing” galaxy evolution. On the other hands, the external (nurture) effects include the recycling of chemically enriched gas due to the higher pressure of inter galactic medium or stripping of outer gas in the reservoir in protoclusters. Although, none of the interpretation is perfect, the external effects such as gas recycling or stripping seem to be favored.