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  1. 020 学位論文
  2. 物理科学研究科
  3. 09 天文科学専攻

Dense Core Survey Toward Nearby Massive Star and Cluster Forming Giant Molecular Clouds: Origin of the Initial Mass Function

https://ir.soken.ac.jp/records/428
https://ir.soken.ac.jp/records/428
a884cd8c-b2c3-499a-b41d-79d5ae222890
名前 / ファイル ライセンス アクション
甲1032_要旨.pdf 要旨・審査要旨 (330.3 kB)
甲1032_本文.pdf 本文 (31.5 MB)
Item type 学位論文 / Thesis or Dissertation(1)
公開日 2010-02-22
タイトル
タイトル Dense Core Survey Toward Nearby Massive Star and Cluster Forming Giant Molecular Clouds: Origin of the Initial Mass Function
タイトル
タイトル Dense Core Survey Toward Nearby Massive Star and Cluster Forming Giant Molecular Clouds: Origin of the Initial Mass Function
言語 en
言語
言語 eng
資源タイプ
資源タイプ識別子 http://purl.org/coar/resource_type/c_46ec
資源タイプ thesis
著者名 池田, 紀夫

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池田, 紀夫

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フリガナ イケダ, ノリオ

× イケダ, ノリオ

イケダ, ノリオ

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著者 IKEDA, Norio

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en IKEDA, Norio

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学位授与機関
学位授与機関名 総合研究大学院大学
学位名
学位名 博士(理学)
学位記番号
内容記述タイプ Other
内容記述 総研大甲第1032号
研究科
値 物理科学研究科
専攻
値 09 天文科学専攻
学位授与年月日
学位授与年月日 2007-03-23
学位授与年度
値 2006
要旨
内容記述タイプ Other
内容記述 We have carried out H<sup>13</sup>CO<sup>+</sup>(<i>J</i>=1-0) core unbiased surveys in the nearby<br /> massive star-and cluster-forming giant molecular clouds Orion A,Orion B,<br />and Cepheus OB3. Our observations were carried out using the Nobeyama<br />45 m radio telescope with the 25-BEam Array Receiver System (BEARS).<br />Our surveys are very unique in that large areas (1.4 - 1.5 square degrees)<br /> of the clouds were covered with very high spatial resolution of 20 - 27" <br /> enough to resolve dense cores, and with deep integration (1&sigma;~0.1 K in <i>T</i>*<small>A</small>),<br /> resulting in the sensitive mass detection of 1.6 - 3.5 <i>M</i><small>&Theta;</small> for dense cores in<br />the clouds . These observational advantages allow us to derive reliable core<br />mass functions(CMFs)with a good statistics of sample number~30 - 240<br />and a wide - mass range of 2 &le; <i>M / M</i>&Theta; &le;100.<br /> The morphology of the H<sup>13</sup> CO <sup>+</sup>(<i>J</i>=1 - 0)emission in the Orion A and<br />B is very similar to that of the dust continuum emission. In addition,our<br />observations of the Cepheus cloud is the first unbiased one of the dense gas<br />with such a high spatial resolution.We identified 236,98,and 31 dense cores<br />from our data with the clumpfind algorithm in the Orion A,B,and Cepheus <br />OB3, respectively. All the cores seem to be almost in virial equilibrium<br />independently of whether the cores are thermal or turbulent. Furthermore,<br />the majority of the cores in the three clouds has very similar distributions<br />of the physical parameters. This suggests that the most of the cores are the<br />common ones, while there are a few peculiar cores whose velocity widths and<br />radii are larger than 1 km s<sup>-1</sup> and 0.14 pc, respectively. We derived the<br />H<sup>13</sup>CO<sup>+</sup>CMFs of the clouds and found that these are consistent with those<br />by previous studies in the sense of their power-law indices in the high-mass<br />part of-2.1--2.4 and the existence of turnovers near 5 - 10<i>M</i><small>&Theta;</small>.<br /> We showed that the dust GMF can be produced from the H<sup>13</sup>CO<sup>+</sup> CMF<br />assuming that the dust cores correspond to the inner denser(>10<sup>6</sup> cm<sup>-3</sup>)<br />structures of the H<sup>13</sup>CO<sup>+</sup> ones and the core density profi1e which is propor-<br />tional to R<sup>-2</sup> Furthermore we predicted IMFs from the H<sup>13</sup>CO<sup>+</sup> CMFs in <br />the three clouds assuming that all the cores form stars simultaneously and the<br />star formation efficiency is uniform over the cores. We also considered binary<br />formations assuming that the core multiplicity is uniform over the cores. We <br /> found that the high-mass part power-law slope of the predicted IMFs agree<br />well with that of the Orion Nebula Cluster IMF and of the Galactic-field<br />averaged IMF for a star formation efficiency of ~25 - 50%.These findings<br > suggest that the IMF is determined at the time of the H<sup>13</sup>CO<sup>+</sup> core(the<br />density of~10<sup>4-5 </sup>cm-3 or less)formation,rather than tht of the dust cores<br /> of>10<sup>6</sup>cm<sup>F-3</sup>.<br /> On the other hand,the predicted IMF seem to have less number of stars<br />considerably in the low-mass part below <i>2M</i><small>&Theta;</small>,resulted from the turnover of<br />the CMFs. As one of the possible causes of the CMF turnover,we modeled<br />confusion along the line of sight,mainly due to the shadowing of low-mass<br />cores caused by massive cores.The shadowing-corrected predicted IMFs<br />agree well with the IMFs. We found that the shadowing-corrected CMFs do<br />not have turnovers, suggesting that the apparent turnovers in the observed<br /> CMFs may not correspond to those of the IMFs. On the other hand,their<br />powe-law indices of the shadowing - corrected CMFs are very similar to each<br />other although the three clouds have apparent difference in star-forming ac-<br />tivities. This implies a common core formation processes that is insensitive<br />to environmental parameters,leading to the origin of the universality of the<br />IMF. <br /> We discovered four cores with large velocity widths,significantly wider<br />than those of the other cores,only toward the M42 H <small>II</small> region and the Cep-A<br />compact H<small>II</small> region. The finding of the large-velocity width cores suggests<br />that the energy input from the H<small>II</small> regions increases the velocity width. Since<br />the large-velocity width cores can produce the most massive stars owing to<br />their large mass accretion rates,the massive star formamations in the Orion<br />A and Cepheus OB3 clouds are likely to be caused by the environmental<br />stellar activities.This may imply that the IMF have additional turnover<br />at the high-mass end,although the statistical uncertainties of the observed<br />IMF are too large to recognize the turnover. In the Orion B, on the other<br />hand,there is no core with large velocity width significantly One of the<br />explanations is that stellar activities in the Orion B cloud,in which the most<br />earliest star is O8,are less energetic than those of O6 and O7 in the Orion<br />A and Cepheus,respectively This may indicate that stellar energy sources<br />earlier than O7-O6 are required to influence the moat massive stars of the<br />next generation.<br /> We conclude that the IMF originates from the CMF. It implies that in-<br />vestigating the CMF formation processes is equivalent to revealing the origin<br />of the IMF. We tested the proposed core formation prosesses such as grav-<br />itational fragmentation,collision and coalescence,accretion,and turbulent<br />fragmentation based on our core catalog. We conclude that the turbulent<br />fragmentation is the most plausible one of them.
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