| 研究概要 |
The main research achievements include (1) a first discovery of cosmological infall of member galaxies relative to the hot plasma in galaxy clusters. This means a discovery of one of the largest energy flow ~ 10e37 - 10e38 W per cluster in the Universe. (2) a first discovery of a strong galaxy-hot plasma interaction, i.e., ram pressure stripping, at clusters with redshift of 0.4. Details of the two achievements are as follows.
(1) In collaboration with optical and X-ray astronomers in- and out-side Japan, we studied a galaxy infall phenomenon (proposed in Makishima et al. 2001) using a sample of 34 galaxy clusters with redshift range of 0.1-0.9. In this work I played a central role in analyzing both optical and X-ray data. We have detected, for the first time, a significant evolution spanning a time interval of 6 Gyr: galaxies have been centrally concentrated with time relative to dark matter, while the ICM has been expanding even they keep radiating (Gu et al. 2013a). We introduced our discovery and science view in a press release of Astronomical Society of Japan.
(2) I am leading another research to understand the actual process of the galaxy infall. We discovered, for the first time, a phenomenon of "ram pressure stripping" in nine galaxies belonging to a cluster with redshift of 0.4. Also we detected out-of-galaxy star formation in the nearby Virgo Cluster (Gu et al. 2013b; Yagi et al. 2013).
References: Makishima, K. et al. 2001, PASJ, 53,401; Gu, L. et al. 2013a, ApJ, 767,157; Gu, L. et al. 2013b, ApJ, 777L, 36; Yagi, M. Gu, L. et al. 2013, ApJ, 778, 91
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
1: 当初の計画以上に進展している
理由
As written in the "Research plan and methods" of the Kakenhi proposal, we set three main research topic: (1) continue and enhance the galaxy-infall study; (2) understand how galaxies interact with the hot plasma; and (3) prospect for future studies with the ASTRO-H. The time schedule was designed as follows: in FY 2013 we will mainly focus on topic (1) and start topic (2), while in FY 2014 topic (2) become the main study and topic (1) will be continued and finished. Topic (3) will play a minor role in both year. As I described in summary of research achievements,
we have finished main part of topic (1) and about half of topic (2). This means that we are on schedule.
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| 今後の研究の推進方策 |
Our discovery means the first step towards a systematic understanding of a totally new cosmological baryonic matter evolution on large scales. For the first time, we are tracking, over the cosmological timescale, how the galaxies gradually lose dynamical energy to the surrounding matters in galaxy clusters. We believe one main driving mechanism is a long-range interaction between galaxies and hot plasmas. Since nobody else is yet aware of this simple but attractive scenario, I would like to devote for its further development on following issues.
(1) Much strengthen the galaxy infall scenario by further quantifying the cosmic evolution of three cluster mass components (i.e., galaxy, ICM and dark matter). To derive conclusively the evolution between galaxy and hot plasmas as well as between galaxy and dark matter, we are now analyzing high-quality optical and X-ray data for 340 galaxy clusters. When this "second step" is finished (within FY 2014), our view will be more widely-recognized and become a new research paradigm in cluster astrophysics.
(2) Quantify the amount of galaxy dynamical energy converted to the hot plasma thermal energy. By the 340 cluster sample, we will study the entropy distribution of the hot plasmas and measure, for the first time, the input from galaxies. This work will be finished within FY 2014.
(3) By analyzing joint Subaru and X-ray data, we will study in more clusters the ram pressure strippings. By collaborating with theoreticians and MHD researchers, we will establish the framework on ICM detection which contributes a main science for ASTRO-H.
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