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・宇宙物理学研究系 教授東京大学 大学院理学系研究科 物理学専攻 教授
- 学位
- 博士(理学)(東京大学)修士(理学)(東京大学)
- J-GLOBAL ID
- 200901060914122911
- researchmap会員ID
- 1000363024
- 外部リンク
研究キーワード
5研究分野
1委員歴
3-
2014年4月 - 現在
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2011年9月 - 現在
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2006年 - 2009年
受賞
2論文
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The Astrophysical Journal 974(2) 180-180 2024年10月1日Abstract We investigate the physical origins of the Balmer decrement anomalies in GS-NDG-9422 and RXCJ2248-ID galaxies at z ∼ 6 whose Hα/Hβ values are significantly smaller than 2.7, the latter of which also shows anomalous Hγ/Hβ and Hδ/Hβ values beyond the errors. Because the anomalous Balmer decrements are not reproduced under the Case B recombination, we explore the nebulae with optical depths smaller and larger than the Case B recombination by physical modeling. We find two cases quantitatively explaining the anomalies: (1) density-bounded nebulae that are opaque only up to around Lyγ–Ly8 transitions and (2) ionization-bounded nebulae partly/fully surrounded by optically thick excited H i clouds. The case of (1) produces more Hβ photons via Lyγ absorption in the nebulae, requiring fine tuning in optical depth values, while this case helps ionizing photon escape for cosmic reionization. The case of (2) needs the optically thick excited Hi clouds with N 2 ≃ 1012−1013 cm−2, where N 2 is the column density of the hydrogen atom with the principal quantum number of n = 2. Interestingly, the high N 2 values qualitatively agree with the recent claims for GS-NDG-9422 with the strong nebular continuum requiring a number of 2s-state electrons and for RXCJ2248-ID with the dense ionized regions likely coexisting with the optically thick clouds. While the physical origin of the optically thick excited H i clouds is unclear, these results may suggest gas clouds with excessive collisional excitation caused by an amount of accretion and supernovae in the high-z galaxies.
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Space Telescopes and Instrumentation 2024: Optical, Infrared, and Millimeter Wave 117-117 2024年8月23日
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Space Telescopes and Instrumentation 2024: Optical, Infrared, and Millimeter Wave 116-116 2024年8月23日
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Space Telescopes and Instrumentation 2024: Optical, Infrared, and Millimeter Wave 115-115 2024年8月23日
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Space Telescopes and Instrumentation 2024: Optical, Infrared, and Millimeter Wave 33-33 2024年8月23日
MISC
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宇宙科学技術連合講演会講演集(CD-ROM) 58th 2014年第58回宇宙科学技術連合講演会（2014年11月12日-15日. 長崎ブリックホール), 長崎市, 長崎県資料番号: AC1500019000レポート番号: JSASS-2014-4142
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電子情報通信学会誌 97(11) 958-963 2014年宇宙の歴史の解明,それは現代の天文学の抱える大きな課題の一つである.そのためには,テラヘルツ帯における天体観測が重要な働きをする.宇宙のエネルギー放射の大きな割合が,テラヘルツ帯において,星間塵の熱放射として放射されるからである.ただし,その観測のためには,地球の大気の影響を避け,人工衛星による観測が必要である.日本が主導する「あかり」(2006年打上げ)と,SPICA(2020年代打上げ予定)を中心にテラヘルツ帯での天体観測を行う衛星の実例を紹介する.
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電子情報通信学会技術研究報告 114(48(SANE2014 10-20)) 51-56 2014年次世代赤外線天文衛星SPICAには,絶対温度4.5Kまで冷却する遠赤外線観測装置が搭載される.このため,地球を指向する高利得アンテナによって送信されるX帯RF信号から,これらの観測機器へのエネルギー漏洩を厳しく抑制する必要がある.衛星構造体(CFRP(carbon fiber reinforced plastics), MLI(multi layer insulation)および鏡筒の金属板接合モデル)について,電磁波シールド特性を実験的に測定したので報告する.実測の結果,CFRPとMLIはアルミ合金と同等のシールド特性を持つことがわかった.接合モデルは,締結材の接合間隔を広げるほどシールド効果は低下する.しかしながら,クロメート処理をアルミ表面に施すことにより,アルミ酸化皮膜が形成された状態よりも表面導電率が向上し,シールド特性は改善することがわかった.
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Publications of the Astronomical Society of Japan 65(1) 2013年2月25日We present high-resolution spectroscopy of gaseous CO absorption in the fundamental ro-vibrational band toward the heavily obscured active galactic nucleus (AGN) IRAS 08572+3915. We have detected absorption lines up to highly excited rotational levels (J ≦ 17). The velocity profiles reveal three distinct components, the strongest and broadest (Δv > 200 km s ) of which is due to blueshifted (-160 km s ) gas at a temperature of ~270K absorbing at velocities as high as -400 km s . A much weaker but even warmer (~700 K) component, which is highly redshifted (+100 km s ), is also detected, in addition to a cold (~20 K) component centered at the systemic velocity of the galaxy. On the assumption of local thermodynamic equilibrium, the column density of CO in the 270K component is N ~ 4.5 × 10 cm , which in fully molecular gas corresponds to an H column density of N ~ 2.5 × 10 cm . The thermal excitation of CO up to the observed high rotational levels requires a density greater than n (H ) > 2 × 10 cm , implying that the thickness of the warm absorbing layer is extremely small (Δd < 4 × 10 pc), even if it is highly clumped. The large column densities and high radial velocities associated with these warm components, as well as their temperatures, indicate that they originate in molecular clouds near the central engine of the AGN. © 2013. Astronomical Society of Japan. -1 -1 -1 -1 18 -2 22 -2 7 -3 -2 CO 2 H2 c 2
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Astronomy and Astrophysics 550 2013年Context. Little is known about the properties of the warm (T ≳ 150 K) debris disk material located close to the central star, which has a more direct link to the formation of terrestrial planets than does the low-temperature debris dust that has been detected to date. Aims. To discover new warm debris disk candidates that show large 18 μm excess and estimate the fraction of stars with excess based on the AKARI/IRC Mid-Infrared All-Sky Survey data. Methods. We searched for point sources detected in the AKARI/IRC All-Sky Survey, which show a positional match with A-M dwarf stars in the Tycho-2 Spectral Type Catalogue and exhibit excess emission at 18 μm compared to what is expected from the K magnitude in the 2MASS catalogue. Results. We find 24 warm debris candidates including 8 new candidates among A-K stars. The apparent debris disk frequency is estimated to be 2.8 ± 0.6%. We also find that A stars and solar-type FGK stars have different characteristics of the inner component of the identified debris disk candidates. While debris disks around A stars are cooler and consistent with steady-state evolutionary model of debris disks, those around FGK stars tend to be warmer and cannot be explained by the steady-state model. © 2013 ESO. dust S
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Proceedings of SPIE - The International Society for Optical Engineering 8443 2012年10月16日The joint JAXA/NASA ASTRO-H mission is the sixth in a series of highly successful X-ray missions initiated by the Institute of Space and Astronautical Science (ISAS). ASTRO-H will investigate the physics of the high-energy universe via a suite of four instruments, covering a very wide energy range, from 0.3 keV to 600 keV. These instruments include a high-resolution, high-throughput spectrometer sensitive over 0.3-2 keV with high spectral resolution of Delta E < 7 eV, enabled by a micro-calorimeter array located in the focal plane of thin-foil X-ray optics; hard X-ray imaging spectrometers covering 5-80 keV, located in the focal plane of multilayer-coated, focusing hard X-ray mirrors; a wide-field imaging spectrometer sensitive over 0.4-12 keV, with an X-ray CCD camera in the focal plane of a soft X-ray telescope; and a non-focusing Compton-camera type soft gamma-ray detector, sensitive in the 40-600 keV band. The simultaneous broad bandpass, coupled with high spectral resolution, will enable the pursuit of a wide variety of important science themes.
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電子情報通信学会技術研究報告. SANE, 宇宙・航行エレクトロニクス 112(229) 239-244 2012年10月3日We present the overview and the current status of SPICA (Space Infrared Telescope for Cosmology and Astrophysics), which is a mission optimized for mid- and far-infrared astronomy with a cryogenically cooled 3.2m telescope. SPICA has high spatial resolution and unprecedented sensitivity in the mid- and far-infrared, which will enable us to address a number of key problems in present-day astronomy, ranging from the star-formation history of the universe to the formation of planets. To reduce the mass of the whole mission, SPICA will be launched at ambient temperature and cooled down on orbit by mechanical coolers on board with an efficient radiative cooling system, a combination of which allows us to have a 3-m class cooled (6K) telescope in space with moderate total weight (3.7t). SPICA is proposed as a Japanese-led mission together with extensive international collaboration. ESA's contribution to SPICA has been studied under the framework of the ESA Cosmic Vision. The consortium led by SRON is in charge of a key focal plane instrument SAFARI (SPICA Far-Infrared Instrument). Korea and Taiwan are also important partners for SPICA. US participation to SPICA is under discussion. The SPICA project is now in the "risk mitigation phase". The target launch year of SPICA is 2022.
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Publications of The Korean Astronomical Society 27(4) 111-116 2012年9月19日Far-infrared observations provide crucial data for the investigation and characterisation of the properties of dusty material in the Interstellar Medium (ISM), since most of its energy is emitted between ~100 and 200 um. We present the first all-sky image from a sensitive all-sky survey using the Japanese AKARI satellite, in the wavelength range 50 -- 180 um. Covering >99% of the sky in four photometric bands with four filters centred at 65 um, 90 um, 140 um, and 160 um wavelengths, this achieved spatial resolutions from 1 to 2 arcmin and a detection limit of <10 MJy sr-1, with absolute and relative photometric accuracies of <20%. All-sky images of the Galactic dust continuum emission enable astronomers to map the large-scale distribution of the diffuse ISM cirrus, to study its thermal dust temperature, emissivity and column density, and to measure the interaction of the Galactic radiation field and embedded objects with the surrounding ISM. In addition to the point source population of stars, protostars, star-forming regions, and galaxies, the high Galactic latitude sky is shown to be covered with a diffuse filamentary-web of dusty emission that traces the potential sites of high latitude star formation. We show that the temperature of dust particles in thermal equilibrium with the ambient interstellar radiation field can be estimated by using 90 um, 140 um, and 160 um data. The FIR AKARI full-sky maps provide a rich new data set within which astronomers can investigate the distribution of interstellar matter throughout our Galaxy, and beyond.
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Astrophysical Journal 754(1) 2012年7月20日We investigate the mid- (MIR) to far-infrared (FIR) properties of a nearly complete sample of local active galactic nuclei (AGNs) detected in the Swift/Burst Alert Telescope (BAT) all-sky hard X-ray (14-195keV) survey, based on the cross correlation with the AKARI infrared survey catalogs complemented by those with Infrared Astronomical Satellite and Wide-field Infrared Survey Explorer. Out of 135 non-blazer AGNs in the Swift/BAT nine-month catalog, we obtain the MIR photometric data for 128 sources either in the 9, 12, 18, 22, and/or 25 μm band. We find good correlation between their hard X-ray and MIR luminosities over three orders of magnitude (42 < log λL (9, 18 μm) < 45), which is tighter than that with the FIR luminosities at 90 μm. This suggests that thermal emission from hot dusts irradiated by the AGN emission dominate the MIR fluxes. Both X-ray unabsorbed and absorbed AGNs follow the same correlation, implying isotropic infrared emission, as expected in clumpy dust tori rather than homogeneous ones. We find excess signals around 9 μm in the averaged infrared spectral energy distribution from heavy obscured "new type" AGNs with small scattering fractions in the X-ray spectra. This could be attributed to the polycyclic aromatic hydrocarbon emission feature, suggesting that their host galaxies have strong starburst activities. © 2012. The American Astronomical Society. All rights reserved. λ
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Astrophysical Journal 753(2) 2012年7月10日We combine data from two all-sky surveys in order to study the connection between the infrared and hard X-ray (>10keV) properties for local active galactic nuclei (AGNs). The Swift Burst Alert Telescope all-sky survey provides an unbiased, flux-limited selection of hard X-ray-detected AGNs. Cross-correlating the 22month hard X-ray survey with the AKARI all-sky survey, we studied 158 AGNs detected by the AKARI instruments. We find a strong correlation for most AGNs between the infrared (9, 18, and 90 μm) and hard X-ray (14-195keV) luminosities, and quantify the correlation for various subsamples of AGNs. Partial correlation analysis confirms the intrinsic correlation after removing the redshift contribution. The correlation for radio galaxies has a slope and normalization identical to that for Seyfert 1 galaxies, implying similar hard X-ray/infrared emission processes in both. In contrast, Compton-thick (CT) sources show a large deficit in the hard X-ray band, because high gas column densities diminish even their hard X-ray luminosities. We propose two photometric diagnostics for source classification: one is an X-ray luminosity versus infrared color diagram, in which type 1 radio-loud AGNs are well isolated from the others in the sample. The other uses the X-ray versus infrared color as a useful redshift-independent indicator for identifying CT AGNs. Importantly, CT AGNs and starburst galaxies in composite systems can also be differentiated in this plane based upon their hard X-ray fluxes and dust temperatures. This diagram may be useful as a new indicator to classify objects in new and upcoming surveys such as WISE and NuSTAR. © 2012. The American Astronomical Society. All rights reserved..
共同研究・競争的資金等の研究課題
49-
日本学術振興会 科学研究費助成事業 2023年4月 - 2028年3月
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日本学術振興会 科学研究費助成事業 2023年4月 - 2027年3月
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日本学術振興会 科学研究費助成事業 2024年4月 - 2027年3月
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日本学術振興会 科学研究費助成事業 2023年4月 - 2026年3月
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日本学術振興会 科学研究費助成事業 2023年6月 - 2025年3月
● 専任大学名
1-
専任大学名東京大学（University of Tokyo)
