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arXiv · 0810.0529

Galaxy Clusters at 0.9<z<1.7 in the AKARI NEP deep field

Tomotsugu Goto·Hitoshi Hanami·Myungshin Im·Koji Imai·Hanae Inami·Tsuyoshi Ishigaki·Hyung Mok Lee·Hideo Matsuhara·Takao Nakagawa·Youichi Ohyama·Shinki Oyabu·Chris P. Pearson·Toshinobu Takagi·Takehiko Wada
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Abstract

There is a huge gap between properties of red-sequence selected massive galaxy clusters at z<1 and Lyman-break selected proto-clusters at z>3. It is important to understand when and how the z>3 proto-clusters evolve into passive clusters at z<1. We aim to fill this cluster desert by using the space-based N4(4um) imaging with the AKARI. The z'-N4 color is a powerful separator of cluster galaxies at z>1, taking advantage of the 4000A break and the 1.6um bump. We carefully selected 16 promising cluster candidates at 0.9<z<1.7, which all show obvious over-density of galaxies and a prominent red-sequence. At this redshift range, the mid-infrared S15um/S9um flux ratio is an extinction-free indicator of galaxy star formation activity due to the redshifted PAH emission lines (6.2,7.7 and 8.6um). We show statistically that the cluster galaxies have a lower S15um/S9um flux ratio than field galaxies, i.e., cluster galaxies already have lower star-formation activity at 0.9<z<1.7, pushing the formation epoch of these galaxy clusters to a higher redshift.

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Tomotsugu Goto, Hitoshi Hanami, Myungshin Im, Koji Imai, Hanae Inami, Tsuyoshi Ishigaki, Hyung Mok Lee, Hideo Matsuhara, Takao Nakagawa, Youichi Ohyama, Shinki Oyabu, Chris P. Pearson, Toshinobu Takagi, Takehiko Wada. 2008-10-02. Galaxy Clusters at 0.9<z<1.7 in the AKARI NEP deep field. https://doi.org/10.1093/pasj/60.sp2.s531

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