研究者業績
基本情報
- 所属
- 国立研究開発法人宇宙航空研究開発機構 宇宙科学研究所 助教総合研究大学院大学 物理科学研究科 助教
- 学位
- 理学博士(1998年3月)
- J-GLOBAL ID
- 200901028844431929
- researchmap会員ID
- 5000050859
- 外部リンク
銀河、銀河団などの宇宙の大規模構造の形成と進化の研究。主にX線による観測を手段とします。
愛知県一宮高校卒業、
名古屋大学 理学部卒業、
東京大学理学系研究科 理学博士取得、
宇宙科学研究所、SRON(NL)にてポスドク。
現在、JAXA/宇宙科学研究所勤務。
愛知県一宮高校卒業、
名古屋大学 理学部卒業、
東京大学理学系研究科 理学博士取得、
宇宙科学研究所、SRON(NL)にてポスドク。
現在、JAXA/宇宙科学研究所勤務。
研究分野
2経歴
7-
2020年11月 - 現在
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2020年11月 - 現在
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2020年9月 - 現在
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2007年4月 - 現在
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2020年11月 - 2021年3月
受賞
3主要な論文
74-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 71(3) 2018年11月 査読有りWe present results of a search for unidentified line emission and absorption signals in the 2-12keV energy band of spectra extracted from Perseus Cluster core region observations obtained with the 5eV energy resolution Hitomi Soft X-ray Spectrometer. No significant unidentified line emission or absorption is found. Line flux upper limits (1 sigma per resolution element) vary with photon energy and assumed intrinsic width, decreasing from 100 photons cm$^{-2}$ s$^{-1}$ sr $^{-1}$ at 2keV to $<10$ cm$^{-2}$ s$^{-1}$ sr $^{-1}$ over most of the 5-10 keV energy range for a Gaussian line with Doppler broadening of 640 km/s. Limits for narrower and broader lines have a similar energy dependence and are systematically smaller and larger, respectively. These line flux limits are used to constrain the decay rate of hypothetical dark matter candidates. For the sterile neutrino decay rate, new constraints over the the mass range of 4-24 keV with mass resolution better than any previous X-ray analysis are obtained. Additionally, the accuracy of relevant thermal spectral models and atomic data are evaluated. The Perseus cluster spectra may be described by a composite of multi-temperature thermal and AGN power-law continua. Superposed on these, a few line emission signals possibly originating from unmodeled atomic processes (including Si XIV and Fe XXV) are marginally detected and tabulated. Comparisons with previous X-ray upper limits and future prospects for dark matter searches using high-energy resolution spectroscopy are discussed....
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The Astrophysical Journal 837(1) L15-L15 2016年7月25日High-resolution X-ray spectroscopy with Hitomi was expected to resolve the origin of the faint unidentified E=3.5 keV emission line reported in several low-resolution studies of various massive systems, such as galaxies and clusters, including the Perseus cluster. We have analyzed the Hitomi first-light observation of the Perseus cluster. The emission line expected for Perseus based on the XMM-Newton signal from the large cluster sample under the dark matter decay scenario is too faint to be detectable in the Hitomi data. However, the previously reported 3.5 keV flux from Perseus was anomalously high compared to the sample-based prediction. We find no unidentified line at the reported high flux level. Taking into account the XMM measurement uncertainties for this region, the inconsistency with Hitomi is at a 99% significance for a broad dark-matter line and at 99.7% for a narrow line from the gas. We do not find anomalously high fluxes of the nearby faint K line or the Ar satellite line that were proposed as explanations for the earlier 3.5 keV detections. We do find a hint of a broad excess near the energies of high-n transitions of Sxvi (E=3.44 keV rest-frame) -- a possible signature of charge exchange in the molecular nebula and another proposed explanation for the unidentified line. While its energy is consistent with XMM pn detections, it is unlikely to explain the MOS signal. A confirmation of this interesting feature has to wait for a more sensitive observation with a future calorimeter experiment.
MISC
87-
Astronomy and Astrophysics 433(1) 101-111 2004年12月9日We investigate temperature and entropy profiles of 13 nearby cooling flow clusters observed with the EPIC cameras of XMM-Newton. When normalized and scaled by the virial radius the temperature profiles turn out to be remarkably similar. At large radii the temperature profiles show a clear decline starting from a break radius at ~ 0.1 r_vir. The temperature decreases by ~30 % between 0.1 r_vir and 0.5 r_vir. As expected for systems where non-gravitational processes are of great importance, the scale length characterizing the central temperature drop is not found to be proportional to the virial radius of the system. The entropy of the plasma increases monotonically moving outwards almost proportional to the radius and the central entropy level is tightly correlated with the core radius of the X-ray emission. The dispersion in the entropy profiles is smaller if the empirical relation S \propto T^{0.65} is used instead of the standard self-similar relation S \propto T and, as expected for cooling flow clusters, no entropy cores are observed.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 56(5) L29-L34 2004年10月To detect a warm-hot intergalactic medium (WHIM) associated with the large-scale structure of the universe, we observed a quasar behind the Virgo cluster with XMM-Newton. With 54 ks exposure, we marginally detected an O VIII Kalpha absorption line at 650.9(-1.9)(+0.8) eV in the RGS spectra, with a statistical confidence of 96.4%. The observed line center energy is consistent with the redshift of M 87, and hence the absorber is associated with the Virgo cluster. From the curve of growth, the O VIII column density was estimated to be greater than or equal to 7 x 10(16) cm(-2). In the EPIC spectra, excess emission was found after evaluating the hot ICM in the Virgo cluster and various background components. We inspected the RASS map of the diffuse soft X-ray background, and confirmed that the level of the north and west regions just outside of the Virgo cluster is consistent with the background model that we used, while that of the east side is significantly higher and the enhancement is comparable with the excess emission found in the EPIC data. We consider a significant portion of the excess emission to be associated with the Virgo cluster, although a possible contribution from the North Polar Spur cannot be excluded. Using the column density and the emission measure and assuming an oxygen abundance of 0.1 and an ionization fraction of 0.4, we estimate that the mean electron density and the line-of-sight distance of the warm-hot gas are less than or equal to 6 x 10(-5) cm(-3) and greater than or equal to 9 Mpc. These strongly suggest detection of a WHIM in a filament associated with the Virgo cluster.
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2003年9月30日We present XMM-Newton Reflection Grating Spectrometer observations of X-ray clusters and groups of galaxies. We demonstrate the failure of the standard cooling-flow model to describe the soft X-ray spectrum of clusters of galaxies. We also emphasize several new developments in the study of the soft X-ray spectrum of cooling flows. Although there is some uncertainty in the expected mass deposition rate for any individual cluster, we show that high resolution RGS spectra robustly demonstrate that the expected line emission from the isobaric cooling-flow model is absent below 1/3 of the background temperature rather than below a fixed temperature in all clusters. Furthermore, we demonstrate that the best-resolved cluster spectra are inconsistent with the predicted shape of the differential luminosity distribution and the measured distribution is tilted to higher temperatures. These observations create several fine-tuning challenges for current theoretical explanations for the soft X-ray cooling-flow problem. Comparisons between these observations and other X-ray measurements are discussed.
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MATTER AND ENERGY IN CLUSTERS OF GALAXIES, PROCEEDINGS 301 23-36 2003年In many clusters of galaxies, the cooling time at the core of the intracluster medium is much less than the age of the system, suggesting that the the gas should continually lose energy by radiation. Simple thermodynamic arguments then require that the expected "cooling flow" should exhibit a specific spectroscopic signature, characterized by a differential emission measure distribution that is inversely proportional to the cooling function of the plasma. That prediction can be quantitatively tested for the first time by the Reflection Grating Spectrometer (RGS) experiment on XMM-Newton, which provides high resolution X-ray spectra, even for moderately extended sources like clusters. We present RGS data on 14 separate cooling flow clusters, sampling a very wide range in mass deposition rate. Surprisingly, in all cases we find a systematic deficit of low temperature emission relative to the predictions of the cooling flow models. However, we do see evidence for cooling flow gas at temperatures just below the cluster background temperature, T-0, roughly down to T-0/2. These results are difficult to reconcile with most of the possible explanations for the cooling flow problem that have been proposed to date. We also present RGS data on the massive elliptical galaxy NGC 4636. In this case, we detect evidence for resonance emission line scattering of high oscillator strength Fe L-shell emission lines within the gaseous halo of the galaxy. The detection of that effect leads to very tight constraints on physical conditions within the halo. However, here again, the expected signature of a cooling flow is not detected, perhaps suggesting some, fundamental uncertainty in our understanding of radiative cooling in low density cosmic plasmas.
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Publications of the Astronomical Society of Japan 53(3) 401-420 2001年4月4日Results of ASCA X-ray study of central regions of medium-richness clusters of galaxies are summarized, emphasizing differences between cD and non-cD clusters. The intra-cluster medium (ICM) is likely to consist of two (hot and cool) phases within $\sim 100$ kpc of a cD galaxy, where the ICM metallicity is also enhanced. In contrast, the ICM in non-cD clusters appears to be isothermal with little metallicity gradient right to the center. The gravitational potential exhibits a hierarchical nesting around cD galaxies, while a total mass-density profile with a central cusp is indicated for a non-cD cluster Abell~1060. The iron-mass-to-light ratio of the ICM decreases toward the center in both types of clusters, although it is radially constant in peripheral regions. The silicon-to-iron abundance ratio in the ICM increases with the cluster richness, but remains close to the solar ratio around cD galaxies. These overall results are interpreted without appealing to the popular cooling-flow hypothesis. Instead, an emphasis is put on the halo-in-halo structure formed around cD galaxies.
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Astrophys. J. 535 602-614 2000年1月10日
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Astrophysical Journal 525(1) 58-79 1999年5月15日ASCA and ROSAT data of the Centaurus cluster were analyzed. A central excess in the radial brightness profile is found in the hard energy band up to 10keV. This requires a deeper central potential than a King-type one. A double-beta brightness distribution gives a good account of the data. A deprojected energy spectrum within a spherical region of radius 30 kpc at the cluster center indicates that the ICM cannot be isothermal there. Simultaneous fitting of the three (PSPC, GIS, and SIS) energy spectra extracted from the central 3' region showed that a two-temperature model that has temperatures of 1.4keV and 4.4keV and a common metallicity of 1.0 solar with the Galactic absorption gives the best description to the spectra. A cooling-flow spectral model did not give satisfactory fit. A 3-dimensional cluster model incorporating the two-phase picture, the double-beta brightness distribution, and the central metallicity increase reproduced the overall ASCA and ROSAT data successfully. The derived spatial distribution of the dark matter deviates from a King-type profile exhibiting a central excess, which is consistent with the Navvaro-Frenk-White model. The iron is revealed to be more widely spread than stars, which may have been caused by energetic supernovae and the motion of the cD galaxy. Since the derived characteristics of the cool phase including the temperature, angular extent, gas mass, and metallicity, are on a smooth extension of those of inter-stellar medium (ISM) of elliptical galaxies, the cool phase can be regarded as the ISM associated with the cD galaxy. The cool-phase X-ray emission is presumably sustained by energies dissipated by infalling mass to the cD galaxy in the course of cluster evolution.
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PASJ : publications of the Astronomical Society of Japan 50(6) 537-545 1998年12月1日
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 50(1) 187-193 1998年2月11日We analyzed the ASCA X-ray data of 40 nearby clusters of galaxies, whose intracluster-medium temperature distributes in the range of 0.9--10 keV. We measured the Si and Fe abundances of the intracluster medium, spatially averaging over each cluster, but excluding the central $\sim 0.15 h_{50}^{-1}$ Mpc region in order to avoid any possible abundance gradients and complex temperature structures. The Fe abundances of these clusters are 0.2--0.3 solar, with only weak dependence on the temperature of the intracluster medium, hence on the cluster richness. In contrast, the Si abundance is observed to increase from 0.3 to 0.6--0.7 solar from the poorer to richer clusters. These results suggest that the supernovae of both type-Ia and type-II significantly contribute to the metal enrichment of the intracluster medium, with the relative contribution of type-II supernovae increasing towards richer clusters. We suggest a possibility that a considerable fraction of type-II supernova products escaped from poorer systems.
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Proceedings of SPIE - The International Society for Optical Engineering 2518 85-95 1995年12月1日The ASTRO-E satellite is scheduled for launch in 2000 by the Institute of Space and Astronautical Science (ISAS). In this paper the design and performance of the hard x ray detector (HXD) developed for ASTRO-E are described. The HXD is a combination of YAP/BGO phoswich scintillators and silicon PIN diodes covering a wide energy band of 10 - 700 keV. The detector background is reduced down to several times 10 -6c/s/cm 2/keV, and the sensitivity of the HXD is more than one order of magnitude higher than any other past missions in the range of a few 10 keV to several 100 keV. Thus ASTRO-E HXD is expected to achieve an extreme high performance for detecting cosmic hard x rays and low-energy gamma rays. Astrophysics to be explored with the HXT are expected to be extremely widespread and rich.
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MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 268(3) L55-L59 1994年6月A serendipitous observation of the Seyfert 2 galaxy NGC 6552 by the ASCA Gas Imaging Spectrometer shows this object to have a remarkable X-ray spectrum. It displays a strong Ka line of neutral iron, in addition to low-energy structure. Here we present a model in which reflection from neutral matter dominates the X-ray spectrum. The model includes fluorescence of C, O, Ne, Mg, Si, S, Ar, Ca, Cr, Fe and Ni. A good fit is obtained by assuming that the reflector is of cosmic abundance in these elements; the data require that the iron abundance be within a factor of 2 of the cosmic value. The reflector orientation and the possibility of constraining abundances further are discussed. The implication of such reflection-dominated sources for the X-ray background is also discussed.
書籍等出版物
1講演・口頭発表等
4-
電子情報通信学会 衛星通信研究会（SAT） 2023年5月26日 招待有り
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IAU Symposium 342 – Perseus in Sicily: 2018年5月13日
担当経験のある科目(授業)
2-
2022年5月 - 2022年5月宇宙地球系物理学概論のゲストスピーカー (2022-5-26) (立教大学理学部)
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2020年4月 - 2021年3月基礎物理 (サレジオ工業高等専門学校)
所属学協会
2-
2022年4月 - 現在
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2021年7月 - 現在
共同研究・競争的資金等の研究課題
7-
日本学術振興会 科学研究費助成事業 学術変革領域研究(A) 2020年11月 - 2025年3月
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日本学術振興会 科学研究費助成事業 基盤研究(C) 2014年4月 - 2018年3月
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日本学術振興会 科学研究費助成事業 基盤研究(C) 2012年4月 - 2015年3月
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日本学術振興会 科学研究費助成事業 2007年 - 2009年
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文部科学省 科学研究費補助金(若手研究(B)) 2004年 - 2006年
