High‐Mass Cloud Cores in the η Carinae Giant Molecular Cloud

Abstract

We carried out an unbiased survey for massive dense cores in the giant molecular cloud associated with η Carinae with the NANTEN telescope in 12 CO, 13 CO, and C 18 O J = 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 ⊙ , 1.3×10 22 cm −2 , and 1.2×10 3 cm −3 , respectively. Two of the 15 cores are associated with IRAS point sources whose luminosities are larger than 10 4 L ⊙ , which indicates that massive star formation is occuring within these cores. Five cores including the two with IRAS sources are associated with MSX point sources. We detected H 13 CO + (J = 1-0) emission toward 4 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 = 2-1), which indicates that star formation is also occuring in the core, and the other three of the four H 13 CO + detections show wing-like emission. In total, six C 18 O cores out of 15 (= 40%) are experienced star formation, and at least 2 of 15 (= 13 %) are massive-star forming cores in the η Car GMC. We found that massive star formation occurs preferentially in cores with larger N (H 2 ), M , n(H 2 ), and smaller ratio of M vir /M . We also found that the cores in the η 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 η Car GMC. We found that turbulence injection from stellar winds, molecular outflows, and supernova remnants which originated from stars formed within the GMC, are not enough to explain the existing turbulence. We propose the possibility that the large turbulence was pre-existing 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.

Herschelfar-infrared observations of the Carina Nebula complex

“…The idea that the Gum 31 bubble is part of the giant Carina Nebula cloud complex is supported by the available information about the radial velocities of the molecular clouds. According to the CO maps of Yonekura et al (2005), the clouds surrounding Gum 31 have radial velocities in the range V LSR = −24 · · · − 21 km s −1 , which is very similar to that of the clouds in the central regions of the Carina Nebula, for which a range of V LSR = −26 · · · − 18 km s −1 is found. Another interesting aspect is that the densest and most massive parts of this bubble are found at the south and southeastern regions of the rim, i.e., just along a line connecting the center of the bubble to the center of the Carina Nebula.…”

“…The amount of the molecular gas can be inferred from molecular line observations. Yonekura et al (2005) presented a wide-field 12 CO (J = 1−0) survey of the CNC and determined the total gas masses in different sub-regions. Our 1 degree region we used for our CNC mass estimates includes their regions No 1−3, 7, as well as some parts of their region 4 (see their Table 1 and Fig.…”

“…The CNC contains large amounts of gas and dust clouds, with an estimated total mass in the range 350 000−670 000 M based on CO radio maps (e.g. Grabelsky et al 1988;Yonekura et al 2005;Smith & Brooks 2007). The very strong radiative and wind feedback from the massive stars has already dispersed much of the original cloud mass in the central region, and drives a large expanding superbubble, extending over ∼80 pc (corresponding to ∼2 • ).…”

870μm continuum observations of the bubble-shaped nebula Gum 31

“…A comparison between the 870 μm emission and the 250 μm and 500 μm emissions in the southern part of the nebula (Dec ∼ −58 • 46 00 ) shows that the area mapped with LABOCA almost covers the whole cold dust in the region. Since the emission at 250 μm and 500 μm is extremely faint at the eastern and northeastern regions of Gum 31, where no CO(1−0) emission was detected either (Yonekura et al 2005, CNAV08), we infer that there is little dense molecular gas/dust in the unmapped area of the Hii region (see Sect. 3.3.4).…”

The VISTA Carina Nebula Survey

“…6) show that the Gum 31 region around the stellar cluster NGC 3324 seems to be connected to the central region of the Carina nebula. The CO maps of Yonekura et al (2005) …”