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etaCarGMC - The Astrophysical Journal 634:476494 2005...

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HIGH-MASS CLOUD CORES IN THE ± CARINAE GIANT MOLECULAR CLOUD Yoshinori Yonekura, 1 Shin’ichiro Asayama, 1,2 Kimihiro Kimura, 1 Hideo Ogawa, 1 Yoko Kanai, 3 Nobuyuki Yamaguchi, 2,3 Peter J. Barnes, 4,5 and Yasuo Fukui 3 Recei v ed 2004 October 26; accepted 2005 Au g ust 2 ABSTRACT We carried out an unbiased survey for massive dense cores in the giant molecular cloud associated with ± Carinae with the NANTEN telescope in the 12 CO, 13 CO, and C 18 O J ¼ 1 0 emission lines. We identified 15 C 18 O cores, whose typical line width ± V comp , radius r , mass M , column density N (H 2 ), and average number density n (H 2 ) were 3.3 km s ± 1 , 2.2 pc, 2 : 6 ; 10 3 M ² , 1 : 3 ; 10 22 cm ± 2 , and 1 : 2 ; 10 3 cm ± 3 , respectively. Two of the 15 cores are as- sociated with IRAS point sources whose luminosities are larger than 10 4 L ² , which indicates that massive star formation is occurring within these cores. Five cores, including the two with IRAS sources, are associated with MSX point sources. We detected H 13 CO + ( J ¼ 1 0) emission toward four C 18 O cores, two of which are associated with IRAS and MSX point sources; another one is associated only with an MSX point source, and the other is associated with neither IRAS nor MSX point sources. The core with neither IRAS nor MSX point sources shows the presence of a bipolar molecular outflow in 12 CO ( J ¼ 2 1), which indicates that star formation is also occurring in the core, and the other three of the four H 13 CO + detections show winglike emission. In total, 6 C 18 O cores out of 15 (=40%) have experienced star formation, and at least 2 of 15 (=13%) are massive star–forming cores in the ± Car GMC. We found that massive star formation occurs preferentially in cores with larger N (H 2 ), M , and n (H 2 ) and a smaller ratio of M vir / M . We also found that the cores in the ± Car GMC are characterized by large ± V and M vir / M on average compared to the cores in other GMCs observed with the same telescope. These properties of the cores may account for the fact that as much as 60%–87% of the cores do not show any signs of massive star formation. We investigated the origin of a large amount of turbulence in the ± Car GMC. We found that turbulence injection from stellar winds, molecular outflows, and supernova remnants that originated from stars formed within the GMC are not enough to explain the existing turbu- lence. We propose the possibility that the large turbulence was preexisting when the GMC was formed and is now dissipating. Mechanisms such as multiple supernova explosions in the Carina flare supershell may have contributed to form a GMC with a large amount of turbulence. Subject headin g g s: ISM: clouds — ISM: individual ( ± Carinae GMC) — ISM: molecules — radio lines: ISM — stars: formation 1. INTRODUCTION It is well established that massive stars form in dense cores within giant molecular clouds (GMCs), while low-mass stars form in both dark clouds and GMCs. The formation process of an isolated low-mass star is fairly well understood: the gravita- tional collapse of a molecular cloud into a protostellar core and
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