Details of a Researcher - Oka, Tomoharu

Formation Process of Supermassive Black Holes in Galactic Nuclei,

2006

-

Present
Observational Study of Interstellar Matter in the Galactic Center Region,

1996

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Present

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Books 【 Display / hide 】

銀河の中心に潜むもの　ブラックホールと重力波の謎にいどむ

OKA Tomoharu, 慶應義塾大学出版会, 2018.01
人物でよむ物理法則の事典

Tomato Yonezawa, Kazuhiko Tsuji, etc., Asakura Publishing Co., Ltd., 2015.11

Scope: R. W. ウィルソン、エディントン、オテルマ、B. P. シュミット、チャンドラセカール、ディッケ、ホイヘンス

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Papers 【 Display / hide 】

Discovery of a molecular cloud possibly associated with the youngest Galactic SNR G1.9+0.3

Enokiya R., Sano H., Filipović M.D., Alsaberi R.Z.E., Inoue T., Oka T.

Publications of the Astronomical Society of Japan （Publications of the Astronomical Society of Japan) 75 （ 5 ） 970 - 985 2023.10

ISSN 00046264

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The youngest known Galactic supernova remnant (SNR) G1.9+0.3 has high-velocity supernova shock beyond 10000 km s−1, and it is considered to be one of the major candidates of a PeVatron. Despite these outstanding properties, the surrounding interstellar matter of this object is poorly understood. We investigated the interstellar gas toward G1.9+0.3 using the 12CO(J = 3−2) data with the angular resolution of 15◦ obtained by the CHIMPS2 survey by the James Clerk Maxwell Telescope, and discovered three individual clouds at −1, 7, and 45 km s−1. From its morphological and velocity structures, the −1 km s−1 cloud, having the largest velocity width >20 km s−1 and located at the distance of the Galactic Center, is possibly associated with the SNR. The associated cloud shows a cavity structure both in space and velocity and coincides well with the SNR. We found that the associated cloud has higher column densities toward three bright, radio synchrotron-emitted rims where the radial expansion velocity of the supernova shock is decelerated, and the cloud is faint in the other parts of the SNR. This is the first direct evidence indicating that the highly anisotropic expansion of G1.9+0.3 observed by previous studies results from the deceleration by the interaction between the supernova shock and surrounding dense interstellar medium.
- Access to Document (DOI)
ALMA View of the High-velocity-dispersion Compact Cloud CO 0.02-0.02 at the Galactic Center

Iwata Y., Oka T., Takekawa S., Tsujimoto S., Enokiya R.

Astrophysical Journal （Astrophysical Journal) 950 （ 1 ） 2023.06

ISSN 0004637X

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We report the results of observations toward the center of the molecular cloud CO 0.02-0.02 made using the Atacama Large Millimeter/Submillimeter Array. The successfully obtained 1″ resolution images of CO J = 3-2, H13CN J = 4-3, H13CO+ J = 4-3, SiO J = 8-7, CH3OH J K a, K c = 71,7-61,6 A+ lines, and 900 μm continuum show several new features, which have not been identified in previous observations. The dense gas probe (H13CN, SiO, CH3OH) images are dominated by a pair of northeast-southwest elongated filaments, which may be the main body of CO 0.02-0.02. Two striped patterns perpendicular to each other (F1 and F2) and a high-velocity feature (HV), which appear in different velocity ranges, were prominent in the CO image. An emission hole that may represent an expanding feature was found in the F1 velocity range. F2 appeared to align along the western edge of a 20 pc × 13 pc ellipse (the Large Shell) identified in the single-dish CO map. The HV contains eight compact clumps at the positive high-velocity end of the CO emissions. Based on these results, we propose a formation scenario for CO 0.02-0.02; internal explosions of supernovae, external perturbations by the Large Shell, and gravitational acceleration by a less-luminous star cluster have formed CO 0.02-0.02 in its current state.
- Access to Document (DOI)
Discovery of the Tadpole Molecular Cloud near the Galactic Nucleus

Kaneko M., Oka T., Yokozuka H., Enokiya R., Takekawa S., Iwata Y., Tsujimoto S.

Astrophysical Journal （Astrophysical Journal) 942 （ 1 ） 2023.01

ISSN 0004637X

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In this paper, we report the discovery of an isolated, peculiar compact cloud with a steep velocity gradient at 2.′6 northwest of Sgr A*. This “Tadpole” molecular cloud is unique owing to its characteristic head-tail structure in the position-velocity space. By tracing the CO J = 3-2 intensity peak in each velocity channel, we noticed that the kinematics of the Tadpole can be well reproduced by a Keplerian motion around a point-like object with a mass of 1 × 105 M ⊙. Changes in line intensity ratios along the orbit are consistent with the Keplerian orbit model. The spatial compactness of the Tadpole and absence of bright counterparts in other wavelengths indicate that the object could be an intermediate-mass black hole.
- Access to Document (DOI)
Catalog of High-velocity Dispersion Compact Clouds in the Central Molecular Zone of Our Galaxy

Oka T., Uruno A., Enokiya R., Nakamura T., Yamasaki Y., Watanabe Y., Tokuyama S., Iwata Y.

Astrophysical Journal, Supplement Series （Astrophysical Journal, Supplement Series) 261 （ 2 ） 2022.08

ISSN 00670049

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This study developed an automated identification procedure for compact clouds with broad velocity widths in the spectral-line data cubes of highly crowded regions. The procedure was applied to the CO J = 3 - 2 line data, obtained using the James Clerk Maxwell Telescope, to identify 184 high-velocity dispersion compact clouds (HVDCCs), which are a category of peculiar molecular clouds found in the central molecular zone of our Galaxy. A list of HVDCCs in the area -1.°4 ≤ l ≤ +2.°0, -0.°25 ≤ b ≤ +0.°25 was presented with their physical parameters, CO J = 3 - 2/J = 1 - 0 intensity ratios, and morphological classifications. Consequently, the list provides several intriguing sources that may have been driven by encounters with pointlike massive objects, local energetic events, or cloud-to-cloud collisions.
- Access to Document (DOI)
New Look at the Molecular Superbubble Candidate in the Galactic Center

Tsujimoto S., Oka T., Takekawa S., Iwata Y., Uruno A., Yokozuka H., Nakagawara R., Watanabe Y., Kawakami A., Nishiyama S., Kaneko M., Kanno S., Ogawa T.

Astrophysical Journal （Astrophysical Journal) 910 （ 1 ） 2021.03

ISSN 0004637X

　View Summary

The l = +1.3 region in the Galactic center is characterized by multiple shell-like structures and their extremely broad velocity widths. We revisit the molecular superbubble hypothesis for this region, based on high-resolution maps of CO J = 1-0, 13CO J = 1-0, H13CN J = 1-0, H13CO+ J = 1-0, SiO J = 2-1, and CS J = 2-1 lines obtained from the Nobeyama Radio Observatory 45 m telescope, as well as CO J = 3-2 maps obtained from the James Clerk Maxwell telescope. We identified 11 expanding shells with total kinetic energy and typical expansion time E kin ∼ 1051.9 erg and t exp ∼ 104.9 yr, respectively. In addition, the l = +1.3 region exhibited high SiO J = 2-1/H13CN J = 1-0 and SiO J = 2-1/H13CO+ J = 1-0 intensity ratios, indicating that the region has experienced dissociative shocks in the past. These new findings confirm the molecular superbubble hypothesis for the l = +1.3 region. The nature of the embedded star cluster, which may have supplied 20-70 supernova explosions within 105 yr, is discussed. This work also shows the importance of compact broad-velocity-width features in searching for localized energy sources hidden behind severe interstellar extinction and stellar contamination.
- Access to Document (DOI)

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Papers, etc., Registered in KOARA 【 Display / hide 】

Search for isolated black holes in the Milky Way galaxy based on molecular spectral line observations

Oka, Tomoharu

学事振興資金研究成果実績報告書（慶應義塾大学) 2019
Intensive observations of the intermediate-mass black hole candidate CO-0.40-0.22*

Oka, Tomoharu

学事振興資金研究成果実績報告書（慶應義塾大学) 2018
Search for intermediate-mass black holes in the galactic center based on molecular line observations

Oka, Tomoharu

科学研究費補助金研究成果報告書 2017
Search for super star clusters and intermediate-mass black holes in the depths of our galaxy

Oka, Tomoharu

科学研究費補助金研究成果報告書 2014
Observational Study of the Galactic Nuclues Sgr A* : Mass Accretion and Evolution

OKA, TOMOHARU

科学研究費補助金研究成果報告書 2008

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Reviews, Commentaries, etc. 【 Display / hide 】

銀河系中心のもう一つのブラックホール

OKA Tomoharu

パリティ (Maureen Publishing Co., Ltd.) 32 ( 1 ) 58 - 60 2016.12

Article, review, commentary, editorial, etc. (trade magazine, newspaper, online media), Single Work
Atomic Carbon in the Galaxy

OKA Tomoharu

The Astronomical Herald 99 ( 4 ) 190 - 196 2006.03

Article, review, commentary, editorial, etc. (scientific journal), Single Work
超新星残骸と相互作用する星間分子雲

岡朋治、瀬田益道

原子核研究「超高エネルギー天体 (I)」 42 ( 5 ) 141 - 148 1998

Article, review, commentary, editorial, etc. (scientific journal)
Galactic Center Me¥molecular Clouds -- Micro-scale Structure and Physical Conditions --

OKA Tomoharu

天文月報 88 ( 12 ) 506 - 511 1995.11

Article, review, commentary, editorial, etc. (scientific journal)

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Presentations 【 Display / hide 】

ブラックホールとは何か

岡朋治

10MTV オピニオン「大人のための教養講座」,

2019.03
,
Media coverage, イマジニア株式会社
銀河系中心で発見された高速度雲の起源

岡朋治

ブラックホール地平面勉強会＜銀河系中心とJASMINE＞ (慶應義塾大学日吉キャンパス) ,

2018.12
,
Oral presentation (invited, special)
ALMAによる小型高速度コンパクト雲の詳細観測

竹川俊也, 岡朋治, 岩田悠平, 辻本志保, 野村真理子

日本天文学会2018年秋季年会 (千葉大学) ,

2018.09
,
Oral presentation (general)
高速度コンパクト雲CO 0.02-0.02の3 mm帯ラインサーベイ観測

岩田悠平, 岡朋治, Justin A. Roll, 辻本志保, 竹川俊也

日本天文学会2018年秋季年会 (千葉大学) ,

2018.09
,
Oral presentation (general)
高速度コンパクト雲 CO–0.40–0.22 中に発見された点状電波源の観測的研究

岩田悠平, 岡朋治, 杉本知穂, 竹川俊也, 田邊恭介, 三好真

日本天文学会2018年春季年会 (千葉大学) ,

2018.03
,
Oral presentation (general)

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Research Projects of Competitive Funds, etc. 【 Display / hide 】

Search for Missing Black Holes in the Galaxy based on Submillimeter-wave Observations

2020.04

-

2025.03

MEXT,JSPS, Grant-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (A) , Principal investigator
Search for Intermediate-mass Black Holes in the Galactic Center Based on Molecular Line Observations

2015.04

-

2018.03

MEXT,JSPS, Grant-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (B), Principal investigator