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RISS 인기검색어
- 검색키워드
- 저자 : Yusei Koyama (검색결과 3 건)
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PANORAMIC MID-INFRARED VIEWS OF DISTANT CLUSTERS OF GALAXIES WITH AKARI
Yusei Koyama 한국천문학회 2017 天文學論叢 Vol.32 No.1
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 (10' x 10') 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 15 $\mu$m (rest-frame $\approx$ 8 $\mu$m) imaging observation of the RXJ1716+6708 cluster ($z=0.81$) with IRC. We find that 15 $\mu$m-detected cluster member galaxies (with total infrared luminosities of $L_{\rm IR}\gtrsim 10^{11}L_{\odot}$) are most preferentially located in the cluster outskirt regions, whilst such IR-luminous galaxies avoid the cluster centre. Our H$\alpha$ follow-up study of this field confirmed that a significant fraction of 15 $\mu$m-detected cluster galaxies are heavily obscured by dust (with $A_{\rm H\alpha}$$>$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 2--24 $\mu$m. 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.
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PANORAMIC VIEWS OF GALAXY CLUSTER EVOLUTION: GALAXY ECOLOGY
Kodama, Tadayuki,Koyama, Yusei,Hayashi, Masao,Ken-ichi, Tadaki The Korean Astronomical Society 2010 天文學論叢 Vol.25 No.3
Taking the great advantage of Subaru's wide field coverage both in the optical and in the near infrared, we have been providing panoramic views of distant clusters and their surrounding environments over the wide redshift range of 0:4 < z < 3. From our unique data sets, a consistent picture has been emerging that the star forming activity is once enhanced and then truncated in galaxy groups in the outskirts of clusters during the course of cluster assembly at z < 1. Such activity is shifted into cluster cores as we go further back in time to z ~ 1.5. At z = 2 - 2.5, we begin to enter the epoch when massive galaxies are actually forming in the cluster core. And by z ~ 3, we eventually go beyond the major epoch of massive galaxy formation. It is likely that the environmental dependence of star forming activity is at least partly due to the external environmental effects such as galaxy-galaxy interaction in medium density regions at z < 1, while the intrinsic effect of galaxy formation bias overtakes the external effect at higher redshifts, resulting in a large star formation activity in the cluster center.
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A COSMOLOGICAL PAH SURVEY WITH SPICA
Takehiko Wada,Eiichi Egami,Naofumi Fujishiro,Tomotsugu Goto,Masatoshi Imanishi,Hanae Inami,Daisuke Ishihara,Hidehiro Kaneda,Kotaro Kohno,Yusei Koyama,Hideo Matsuhara,Shuji Matsuura,Tohru Nagao,Youichi 한국천문학회 2017 天文學論叢 Vol.32 No.1
We propose a cosmological survey to probe star formation and nuclear activityin galaxies at redshifts of z = 2 - 4 by polycyclic aromatic hydrocarbon(PAH) features usingthe SPICA mid-infrared instrument (SMI)with a spectral resolution of R = 20. We will cover a wavelength range of 20-36 μmthat corresponds to z = 2 - 4 for the PAH features(11.3, 7.7, and 6.2 μm). The sensitivity will be $1\times10^{-19}$ W/m$^2$ (5 $\sigma$)in case of a referencesurvey that covers 4 arcmin$^2$ field in a one-hour observation. It corresponds to L$_{\rm IR}$=$2\times10^{11}$ $L_\odot$ at z=3and will give us more than 10000 galaxies in a 450 hour survey.
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