@misc{oai:ir.soken.ac.jp:00000428, author = {池田, 紀夫 and イケダ, ノリオ and IKEDA, Norio}, month = {2016-02-17, 2016-02-17}, note = {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～10^4-5cm-3 or less）formation，rather than tht of the dust cores
of＞10⁶cm^F-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., 総研大甲第1032号}, title = {Dense Core Survey Toward Nearby Massive Star and Cluster Forming Giant Molecular Clouds: Origin of the Initial Mass Function}, year = {} }