PANORAMIC MID-INFRARED VIEWS OF DISTANT CLUSTERS OF GALAXIES WITH AKARI

Abstract

We present the results of our mid-infrared (MIR) observations of distant clusters of galaxies with AKARI. The wide-field of view of IRC/AKARI (<TEX>$10^{\prime}{\times}10^{\prime}$</TEX>) is ideally suited for studying dust-obscured star-formation (SF) activity of galaxies along the cosmic web in the distant universe. We performed a deep and wide-field <TEX>$15{\mu}m$</TEX> (rest-frame <TEX>${\approx}8{\mu}m$</TEX>) imaging observation of the RXJ1716+6708 cluster (z = 0.81) with IRC. We find that <TEX>$15{\mu}m$</TEX>-detected cluster member galaxies (with total infrared luminosities of <TEX>$L_{IR}{\geq}10^{11}L_{\odot}$</TEX>) are most preferentially located in the cluster outskirt regions, whilst such IR-luminous galaxies avoid the cluster centre. Our <TEX>$H{\alpha}$</TEX> follow-up study of this field confirmed that a significant fraction of <TEX>$15{\mu}m$</TEX>-detected cluster galaxies are heavily obscured by dust (with <TEX>$AH{\alpha}$</TEX>>3 mag in extreme cases). The environment of such dusty star-burst galaxies coincides with the place where we see a sharp "break" of the colour-density relation, suggesting an important link between dust-obscured SF activity and environmental quenching. We also report the discovery of a new cluster candidate around a radio galaxy at z = 1.52 (4C 65.22), where we obtained one of the deepest IRC imaging datasets with all the nine filters at <TEX>$2-24{\mu}m$</TEX>. This field will provide us with the final, excellent laboratory for studying the dust-enshrouded SF activity in galaxies along the cosmic web at the critical epoch of cluster galaxy evolution with AKARI.