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Register a new userMassive star formation in the Carina nebula complex and Gum 31 -- I. The Carina nebula complex
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Herein, we present results from observations of the 12CO (J=1-0), 13CO (J=1-0), and 12CO (J=2-1) emission lines toward the Carina nebula complex (CNC) obtained with the Mopra and NANTEN2 telescopes. We focused on massive-star-forming regions associated with the CNC including the three star clusters Tr14, Tr15, and Tr16, and the isolated WR-star HD92740. We found that the molecular clouds in the CNC are separated into mainly four clouds at velocities -27, -20, -14, and -8 km/s. Their masses are 0.7x10^4Msun, 5.0x10^4 Msun, 1.6x10^4 Msun, and 0.7x10^4 Msun, respectively. Most are likely associated with the star clusters, because of their high 12CO (J=2-1)/12CO (J=1-0) intensity ratios and their correspondence to the Spitzer 8 micron distributions. In addition, these clouds show the observational signatures of cloud--cloud collisions. In particular, there is a V-shaped structure in the position--velocity diagram and a complementary spatial distribution between the -20 km/s cloud and the -14 km/s cloud. Based on these observational signatures, we propose a scenario wherein the formation of massive stars in the clusters was triggered by a collision between the two clouds. By using the path length of the collision and the assumed velocity separation, we estimate the timescale of the collision to be ~1 Myr. This is comparable to the ages of the clusters estimated in previous studies.
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We present the results of analyses of the 12CO (J=1-0), 13CO (J=1-0), and 12CO (J=2-1) emission data toward Gum 31. Three molecular clouds separated in velocity were detected at -25, -20, and -10 km/s . The velocity structure of the molecular clouds in Gum 31 cannot be interpreted as expanding motion. Two of them, the -25 km/s cloud and the -20 km/s cloud, are likely associated with Gum 31, because their 12CO (J=2-1)/12CO (J=1-0) intensity ratios are high. We found that these two clouds show the observational signatures of cloud-cloud collisions (CCCs): a complementary spatial distribution and a V-shaped structure (bridge features) in the position-velocity diagram. In addition, their morphology and velocity structures are very similar to the numerical simulations conducted by the previous studies. We propose a scenario that the -25 km/s cloud and the -20 km/s cloud were collided and triggered the formation of the massive star system HD 92206 in Gum 31. This scenario can explain the offset of the stars from the center and the morphology of Gum 31 simultaneously. The timescale of the collision was estimated to be ~1 Myr by using the ratio between the path length of the collision and the assumed velocity separation. This is consistent with that of the CCCs in Carina Nebula Complex in our previous study.
We report high resolution observations of the $^{12}$CO$(1rightarrow0)$ and $^{13}$CO$(1rightarrow0)$ molecular lines in the Carina Nebula and the Gum 31 region obtained with the 22-m Mopra telescope as part of the The Mopra Southern Galactic Plane CO Survey. We cover 8 deg$^2$ from $l = 285^{circ}$ to 290$^{circ}$, and from $b = -1.5^{circ}$ to +0.5$^{circ}$. The molecular gas column density distributions from both tracers have a similar range of values. By fitting a grey-body function to the observed infrared spectral energy distribution from Herschel maps, we derive gas column densities and dust temperatures. The gas column density has values in the range from $6.3times 10^{20}$ to $1.4times 10^{23}$ cm$^{-2}$, while the dust temperature has values in the range from 17 to 43 K. The gas column density derived from the dust emission is approximately described by a log-normal function for a limited range of column densities. A high-column density tail is clearly evident for the gas column density distribution, which appears to be a common feature in regions with active star formation. There are regional variations in the fraction of the mass recovered by the CO emission lines with respect to the total mass traced by the dust emission. These variations may be related to changes in the radiation field strength, variation of the atomic to molecular gas fraction across the observed region, differences in the CO molecule abundance with respect to H$_{2}$, and evolutionary stage differences of the molecular clouds that compose the Carina Nebula-Gum 31 complex.
We want to characterize the properties of the cold dust clumps in the Carina Nebula Complex (CNC), which shows a very high level of massive star feedback. We derive the Clump Mass Function (ClMF), explore the reliability of different clump extraction algorithms, and investigate the influence of the temperatures within the clouds on the resulting shape of the ClMF. We analyze a 1.25x1.25 deg^2 wide-field sub-mm map obtained with LABOCA (APEX), which provides the first spatially complete survey of the clouds in the CNC. We use the three clump-finding algorithms CLUMPFIND (CF), GAUSSCLUMPS (GC) and SExtractor (SE) to identify individual clumps and determine their total fluxes. In addition to assuming a common `typical temperature for all clouds, we also employ an empirical relation between cloud column densities and temperature to determine an estimate of the individual clump temperatures, and use this to determine individual clump masses. While the ClMF based on the CF extraction is very well described by a power-law, the ClMFs based on GC and SE are better represented by a log-normal distribution. We also find that the use of individual clump temperatures leads to a shallower ClMF slope than the assumption of a common temperature (e.g. 20 K) of all clumps. The power-law of dN/dM propto M^-1.95 we find for the CF sample is in good agreement with ClMF slopes found in previous studies of other regions. The dependence of the ClMF shape (power-law vs. log-normal distribution) on the employed extraction method suggests that observational determinations of the ClMF shape yields only very limited information about the true structure of the cloud. Interpretations of log-normal ClMF shape as a signature of turbulent pre-stellar clouds vs. power-law ClMFs as a signature of star-forming clouds may be taken with caution for a single extraction algorithm without additional information.
We have obtained wide-field thermal infrared (IR) images of the Carina Nebula, using the SPIREX/Abu telescope at the South Pole. Emission from poly-cyclic aromatic hydrocarbons (PAHs) at 3.29um, a tracer of photodissociation regions (PDRs), reveals many interesting well defined clumps and diffuse regions throughout the complex. Near-IR images (1--2um), along with images from the Midcourse Space Experiment (MSX) satellite (8--21um) were incorporated to study the interactions between the young stars and the surrounding molecular cloud in more detail. Two new PAH emission clumps have been identified in the Keyhole Nebula and were mapped in 12CO(2--1) and (1--0) using the SEST. Analysis of their physical properties reveals they are dense molecular clumps, externally heated with PDRs on their surfaces and supported by external pressure in a similar manner to the other clumps in the region. A previously identified externally heated globule containing IRAS 10430-5931 in the southern molecular cloud, shows strong 3.29-, 8- and 21-um emission, the spectral energy distribution (SED) revealing the location of an ultra-compact (UC) HII region. The northern part of the nebula is complicated, with PAH emission inter-mixed with mid-IR dust continuum emission. Several point sources are located here and through a two-component black-body fit to their SEDs, we have identified 3 possible UC HII regions as well as a young star surrounded by a circumstellar disc. This implies that star formation in this region is on-going and not halted by the intense radiation from the surrounding young massive stars.
The Great Nebula in Carina is a superb location in which to study the physics of violent massive star-formation and the resulting feedback effects, including cloud dispersal and triggered star-formation. In order to reveal the cold dusty clouds in the Carina Nebula complex, we used the Large APEX Bolometer Camera LABOCA at the APEX telescope to map a 1.25 deg x 1.25 deg (= 50 x 50 pc^2) region at 870 micrometer. From a comparison to Halpha images we infer that about 6% of the 870 micrometer flux in the observed area is likely free-free emission from the HII region, while about 94% of the flux is very likely thermal dust emission. The total (dust + gas) mass of all clouds for which our map is sensitive is ~ 60 000 Msun, in good agreement with the mass of the compact clouds in this region derived from 13CO line observations. We generally find good agreement in the cloud morphology seen at 870 micrometer and the Spitzer 8 micrometer emission maps, but also identify a prominent infrared dark cloud. Finally, we construct a radiative transfer model for the Carina Nebula complex that reproduces the observed integrated spectral energy distribution reasonably well. Our analysis suggests a total gas + dust mass of about 200000 Msun in the investigated area; most of this material is in the form of molecular clouds, but a widely distributed component of (partly) atomic gas, containing up to ~ 50% of the total mass, may also be present. Currently, only some 10% of the gas is in sufficiently dense clouds to be immediately available for future star formation, but this fraction may increase with time owing to the ongoing compression of the strongly irradiated clouds and the expected shockwaves of the imminent supernova explosions.
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