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学位論文 / Thesis or Dissertation(1) |
| 公開日 |
2010-02-22 |
| タイトル |
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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 |
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タイトル |
Dense Core Survey Toward Nearby Massive Star and Cluster Forming Giant Molecular Clouds: Origin of the Initial Mass Function |
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言語 |
en |
| 言語 |
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言語 |
eng |
| 資源タイプ |
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資源タイプ識別子 |
http://purl.org/coar/resource_type/c_46ec |
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資源タイプ |
thesis |
| 著者名 |
池田, 紀夫
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| フリガナ |
イケダ, ノリオ
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| 著者 |
IKEDA, Norio
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| 学位授与機関 |
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学位授与機関名 |
総合研究大学院大学 |
| 学位名 |
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学位名 |
博士（理学） |
| 学位記番号 |
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内容記述タイプ |
Other |
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内容記述 |
総研大甲第1032号 |
| 研究科 |
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値 |
物理科学研究科 |
| 専攻 |
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値 |
09 天文科学専攻 |
| 学位授与年月日 |
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学位授与年月日 |
2007-03-23 |
| 学位授与年度 |
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値 |
2006 |
| 要旨 |
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内容記述タイプ |
Other |
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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 （1σ～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>Θ</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 ≤ <i>M / M</i>Θ ≤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>Θ</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>Θ</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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有 |
要旨・審査要旨 (330.3 kB)
