The detailed structure of CO in molecular cloud complexes. I - NGC 6334
TL;DR: In this paper, a combination of the optical depth of the H/sub 2/CO absorption and the velocities of the density-sensitive /sup 13/CO lines of the individual components is used to develop a model of the collapse of the overall cloud and the location of the excitation centers within it.
Abstract: Observations of both /sup 12/CO and /sup 13/CO emission and of H/sub 2/CO absorption have been used in conjunction with previous OH, infrared, radio continuum, and optical information to derive a model of the molecular cloud complex associated with the diffuse H II region NGC 6334. This region contains at least four major centers of excitation which lie on or near the major axis of an elliptical cloud which is elongated in the NE--SW direction roughly parallel to and 0/sup 0/.65 above the galactic plane. The extent of the CO emission along the axis is about 45', which corresponds to approx.8 pc at a distance of 0.6 kpc. A combination of the optical depth of the H/sub 2/CO absorption and the velocities of the density-sensitive /sup 13/CO lines of the individual components is used to develop a model of the collapse of the overall cloud and the location of the excitation centers within it. The size of the component which contains the prominent northern OH maser is estimated from the half-intensity contour of the far-infrared emission; it has a radius of about 3'.8 or approx.0.7 pc. The other compact sources are this size or smaller. The measured differences in velocitymore » between the /sup 12/CO and /sup 13/CO lines at the excitation centers might be interpreted as due to expansion within them.« less
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TL;DR: In this article, the results of a new survey of 23 molecular clouds for the Zeeman effect in OH undertaken with the Australia Telescope National Facility Parkes 64 m radio telescope and the National Radio Astronomy Observatory Green Bank 43m radio telescope are presented.
Abstract: We present the results of a new survey of 23 molecular clouds for the Zeeman effect in OH undertaken with the Australia Telescope National Facility Parkes 64 m radio telescope and the National Radio Astronomy Observatory Green Bank 43 m radio telescope. The Zeeman effect was clearly detected in the cloud associated with the H II region RCW 38, with a field strength of 38 ± 3 μG, and possibly detected in a cloud associated with the H II region RCW 57, with a field strength of -203 ± 24 μG. The remaining 21 measurements give formal upper limits to the magnetic field strength, with typical 1 σ sensitivities less than 20 μG. For 22 of the molecular clouds we are also able to determine the column density of the gas in which we have made a sensitive search for the Zeeman effect. We combine these results with previous Zeeman studies of 29 molecular clouds, most of which were compiled by Crutcher, for a comparison of theoretical models with the data. This comparison implies that if the clouds can be modeled as initially spherical with uniform magnetic fields and densities that evolve to their final equilibrium state assuming flux freezing, then the typical cloud is magnetically supercritical, as was found by Crutcher. If the clouds can be modeled as highly flattened sheets threaded by uniform perpendicular fields, then the typical cloud is approximately magnetically critical, in agreement with Shu et al., but only if the true values of the field for the nondetections are close to the 3 σ upper limits. If instead these values are significantly lower (for example, similar to the 1 σ limits), then the typical cloud is generally magnetically supercritical. When all observations of the Zeeman effect are considered, the single-dish detection rate of the OH Zeeman effect is relatively low. This result may be due to low mean field strengths, but a more realistic explanation may be significant field structure within the beam. As an example, for clouds associated with H II regions, the molecular gas and magnetic field may be swept up into a thin shell, which results in a nonuniform field geometry and measurements of the beam-averaged field strength, which are significantly lower than the true values. This effect makes it more difficult to distinguish magnetically subcritical and supercritical clouds.
159 citations
Centre national de la recherche scientifique1, University of Waterloo2, Janssen Pharmaceutica3, École Normale Supérieure4, Herzberg Institute of Astrophysics5, Swedish Space Corporation6, McMaster University7, University of Helsinki8, University of Calgary9, Helsinki University of Technology10, Saint Mary's University11, Swedish National Space Board12, Hoffmann-La Roche13
TL;DR: For the first time, a search has been conducted in our Galaxy for the 119 GHz transition connecting to the ground state of O2, using the Odin satellite as mentioned in this paper, equipped with a sensitive 3 mm receiver (Tsy...
Abstract: For the first time, a search has been conducted in our Galaxy for the 119 GHz transition connecting to the ground state of O2, using the Odin satellite. Equipped with a sensitive 3 mm receiver (Tsy ...
112 citations
TL;DR: In this article, the authors present results from the Austral Winter 2003 observing campaign of SPARO, a 450 μm polarimeter used with a 2 m telescope at the South Pole.
Abstract: We present results from the Austral Winter 2003 observing campaign of SPARO, a 450 μm polarimeter used with a 2 m telescope at the South Pole. We mapped large-scale magnetic fields in four GMCs in the Galactic disk: NGC 6334, the Carina Nebula, G333.6-0.2, and G331.5-0.1. We find a statistically significant correlation of the inferred field directions with the orientation of the Galactic plane. Specifically, three of the four GMCs (NGC 6334 is the exception) have mean field directions that are within 15° of the plane. The simplest interpretation is that the field direction tends to be preserved during the process of GMC formation. We have also carried out an analysis of published optical polarimetry data. For the closest of the SPARO GMCs, NGC 6334, we can compare the field direction in the cloud as measured by SPARO with the field direction in a larger region surrounding the cloud, as determined from optical polarimetry. For purposes of comparison, we also use optical polarimetry to determine field directions for 9-10 other regions of similar size. We find that the region surrounding NGC 6334 is an outlier in the distribution of field directions determined from optical polarimetry, just as the NGC 6334 cloud is an outlier in the distribution of cloud field directions determined by SPARO. In both cases the field direction corresponding to NGC 6334 is rotated away from the direction of the plane by a large angle. This finding is consistent with our suggestion that field direction tends to be preserved during GMC formation. Finally, by comparing the disorder in our magnetic field maps with the disorder seen in magnetic field maps derived from MHD turbulence simulations, we conclude that the magnetic energy density in our clouds is comparable to the turbulent energy density.
92 citations
Cites background or methods from "The detailed structure of CO in mol..."
...Based on the CO map of Dickel et al. (1977), Straw & Hyland (1989) estimate a mass of 1:5 ; 105 M for the entire cloud....
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...The extent of the associated molecular gas is also about 20 pc (Dickel et al. 1977)....
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TL;DR: In this article, the authors made 12 CO 2{1 and 1{0 maps of eleven molecular outflows associated with intermediate to high-mass young stellar objects (YSOs) in order to establish whether the correlations between outflow parameters and source bolometric luminosity hold in the high mass regime.
Abstract: We have made 12 CO 2{1 and 1{0 maps of eleven molecular outflows associated with intermediate to high-mass young stellar objects (YSOs) in order to establish whether the correlations between outflow parameters and source bolometric luminosity hold in the high-mass regime. It is important to consider the eects of Malmquist- type biases when looking at high-mass YSOs, as they are generally much more distant than their low mass counterparts. We therefore chose only objects located at 2 kpc. We nd that the relations show much more scatter than is seen in similar studies of low-mass YSOs. We also nd that the mass-spectrum is signicantly steeper in high-mass outflows, indicating a larger mass-fraction at lower velocities, a low collimation factor (1{2) and no Hubble-like relationship.
87 citations
Cites background from "The detailed structure of CO in mol..."
...Their observations centred on the CO peak position of Dickel et al. (1977), and they did not find a bipolar structure in the high-velocity gas....
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TL;DR: In this article, the authors present results of high-sensitivity, high-resolution, multifrequency VLA observations toward the star-forming complex NGC 6334, and find that the H II region NGC6334E, previously described as spherical, has a shell-like morphology.
Abstract: We present results of high-sensitivity, high-resolution, multifrequency VLA observations toward the star-forming complex NGC 6334. We find that the H II region NGC 6334E, previously described as spherical, has a shell-like morphology. An additional shell-like radio source, G351.02+0.65, is mapped at 330 MHz. Four radio sources in the NGC 6334 complex present shell-like morphology; their diameters vary from 0.12 to 3.5 pc. Compact radio sources are detected at the center of the shells of NGC 6334E and NGC 6334A. These compact sources are believed to be associated with the exciting stars and are probably tracing ionized stellar winds. This is the first time for any H II region that both the shell and the central object are detected simultaneously in the radio. Two compact radio sources are detected toward the NGC 6334I(N) molecular core. One of them lies within 03 of the position of a bright Class II methanol maser, suggesting that the radio source is associated with a young embedded massive star. This is the first detection of a radio continuum source in the NGC 6334I(N) region.
57 citations