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

池田, 紀夫; イケダ, ノリオ; IKEDA, Norio

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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

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Item type

学位論文 / Thesis or Dissertation(1)

公開日

2010-02-22

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

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

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

フリガナ

イケダ, ノリオ

著者

IKEDA, Norio

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

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

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 H13CO＋(J=1-0) core unbiased surveys in the nearby massive star－and cluster－forming giant molecular clouds Orion A，Orion B， and Cepheus OB3.　Our observations were carried out using the Nobeyama 45 m radio telescope with the 25-BEam Array Receiver System (BEARS). Our surveys are very unique in that large areas (1.4 － 1.5 square degrees) of the clouds were covered with very high spatial resolution of 20 － 27" enough to resolve dense cores, and with deep integration （1σ～0.1 K in T*A）， resulting in the sensitive mass detection of 1.6 － 3.5 MΘ for dense cores in the clouds . These observational advantages allow us to derive reliable core mass functions（CMFs）with a good statistics of sample number～30 － 240 and a wide － mass range of 2 ≤ M / MΘ ≤100． 　The morphology of the H13 CO ＋（J＝1 - 0）emission in the Orion A and B is very similar to that of the dust continuum emission. In addition，our observations of the Cepheus cloud is the first unbiased one of the dense gas with such a high spatial resolution．We identified 236，98，and 31 dense cores from our data with the clumpfind algorithm in the Orion A，B，and Cepheus OB3, respectively. All the cores seem to be almost in virial equilibrium independently of whether the cores are thermal or turbulent. Furthermore, the majority of the cores in the three clouds has very similar distributions of the physical parameters. This suggests that the most of the cores are the common ones, while there are a few peculiar cores whose velocity widths and radii are larger than 1 km s-1 and 0.14 pc, respectively. We derived the H13CO＋CMFs of the clouds and found that these are consistent with those by previous studies in the sense of their power-law indices in the high-mass part of－2.1-－2.4 and the existence of turnovers near 5 － 10MΘ. 　We showed that the dust GMF can be produced from the H13CO＋ CMF assuming that the dust cores correspond to the inner denser（＞106 cm－3） structures of the H13CO＋ ones and the core density profi1e which is propor- tional to R－2　Furthermore we predicted IMFs from the H13CO＋ CMFs in the three clouds assuming that all the cores form stars simultaneously and the star formation efficiency is uniform over the cores. We also considered binary formations assuming that the core multiplicity is uniform over the cores. We found that the high－mass part power-law slope of the predicted IMFs agree well with that of the Orion Nebula Cluster IMF and of the Galactic-field averaged IMF for a star formation efficiency of ～25 - 50％．These findings suggest that the IMF is determined at the time of the H13CO＋ core（the density of～104-5 cm-3 or less）formation，rather than tht of the dust cores of＞106cmF-3． 　On the other hand，the predicted IMF seem to have less number of stars considerably in the low-mass part below 2MΘ，resulted from the turnover of the CMFs. As one of the possible causes of the CMF turnover，we modeled confusion along the line of sight，mainly due to the shadowing of low－mass cores caused by massive cores．The shadowing-corrected predicted IMFs agree well with the IMFs. We found that the shadowing－corrected CMFs do not have turnovers, suggesting that the apparent turnovers in the observed CMFs may not correspond to those of the IMFs. On the other hand，their powe-law indices of the shadowing － corrected CMFs are very similar to each other although the three clouds have apparent difference in star－forming ac- tivities.　This　implies　a　common　core　formation processes that is insensitive to environmental parameters，leading to the origin of the universality of the IMF. 　We discovered four cores with large velocity widths，significantly wider than those of the other cores，only toward the M42 H II region and the Cep-A compact HII region.　The finding of the large-velocity width cores suggests that the energy input from the HII regions increases the velocity width. Since the large-velocity width cores can produce the most massive stars owing to their large mass accretion rates，the massive star formamations in the Orion A and Cepheus OB3 clouds are likely to be caused by the environmental stellar activities．This may imply that the IMF have additional turnover at the high-mass end，although the statistical uncertainties of the observed IMF are too large to recognize the turnover. In the Orion B, on the other hand，there is no core with large velocity width significantly One of the explanations is that stellar activities in the Orion B cloud，in which the most earliest star is O8，are less energetic than those of O6 and O7 in the Orion A and Cepheus，respectively This may indicate that stellar energy sources earlier than O7－O6 are required to influence the moat massive stars of the next generation. 　We conclude that the IMF originates from the CMF. It implies that in- vestigating the CMF formation processes is equivalent to revealing the origin of the IMF. We tested the proposed core formation prosesses such as grav- itational fragmentation，collision and coalescence，accretion，and turbulent fragmentation based on our core catalog.　We conclude that the turbulent fragmentation is the most plausible one of them.

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

× 池田, 紀夫

× イケダ, ノリオ

× IKEDA, Norio

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