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Register a new userRotating toroids in G10.62-0.38, G19.61-0.23, and G29.96-0.02
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M.T. Beltran
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Context. In recent years, we have detected clear evidence of rotation in more than 5 hot molecular cores (HMCs). Their identification is confirmed by the fact that the rotation axes are parallel to the axes of the associated bipolar outflows. We have now pursued our investigation by extending the sample to 3 known massive cores, G10.62-0.38, G19.61-0.23, and G29.96-0.02. Aims. We wish to make a thorough study of the structure and kinematics of HMCs and corresponding molecular outflows to reveal possible velocity gradients indicative of rotation of the cores. Methods. We carried out PdBI observations at 2.7 and 1.4~mm of gas and dust with angular resolutions of 2-3, and 1-2, respectively. To trace both rotation and expansion, we simultaneously observed CH3CN, a typical HMC tracer, and 13CO, a typical outflow tracer. Results. The CH3CN(12-11) observations have revealed the existence of clear velocity gradients in the three HMCs oriented perpendicular to the direction of the bipolar outflows. For G19 and G29 the molecular outflows have been mapped in 13CO. The gradients have been interpreted as rotating toroids. The rotation temperatures, used to derive the mass of the cores, have been obtained by means of the rotational diagram method, and lie in the range of 87-244 K. The diameters and masses of the toroids lie in the range of 4550-12600 AU, and 28-415 Msun, respectively. Given that the dynamical masses are 2 to 30 times smaller than the masses of the cores (if the inclination of the toroids with respect to the plane of the sky is not much smaller than 45 degrees), we suggest that the toroids could be accreting onto the embedded cluster. For G19 and G29, the collapse is also suggested by the redshifted absorption seen in the 13CO(2-1) line. We infer that infall onto the embedded (proto)stars must proceed with rates of 1E-2 Msun/yr, and on timescales of the order of 4E3-1E4yr...
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We use the SPIRE Fourier-Transform Spectrometer (FTS) on-board the ESA Herschel Space Telescope to analyse the submillimetre spectrum of the Ultra-compact HII region G29.96-0.02. Spectral lines from species including 13CO, CO, [CI], and [NII] are detected. A sparse map of the [NII] emission shows at least one other HII region neighbouring the clump containing the UCHII. The FTS spectra are combined with ISO SWS and LWS spectra and fluxes from the literature to present a detailed spectrum of the source spanning three orders of magnitude in wavelength. The quality of the spectrum longwards of 100 {mu}m allows us to fit a single temperature greybody with temperature 80.3pm0.6K and dust emissivity index 1.73pm0.02, an accuracy rarely obtained with previous instruments. We estimate a mass of 1500 Msol for the clump containing the HII region. The clumps bolometeric luminosity of 4 x 10^6 Lsol is comparable to, or slightly greater than, the known O-star powering the UCHII region.
Estimating molecular abundances ratios from the direct measurement of the emission of the molecules towards a variety of interstellar environments is indeed very useful to advance in our understanding of the chemical evolution of the Galaxy, and hence of the physical processes related to the chemistry. It is necessary to increase the sample of molecular clouds, located at different distances, in which the behavior of molecular abundance ratios, such as the 13CO/C18O ratio (X), is studied in detail. We selected the well-studied high-mass star-forming region G29.96-0.02, located at a distance of about 6.2 kpc, which is an ideal laboratory to perform this kind of studies. To study the X towards this region it was used 12CO J=3-2 data obtained from COHRS, 13CO and C18O J=3-2 data from CHIMPS, and 13CO and C18O J=2-1 data retrieved from the CDS database (observed with the IRAM 30m telescope). The distribution of column densities and X throughout the molecular cloud was studied based on LTE and non-LTE methods. Values of X between 1.5 to 10.5, with an average of 5, were found, showing that, besides the dependency between X and the galactocentric distance, the local physical conditions may strongly affect this abundance ratio. We found that correlating the X map with the location of the ionized gas and dark clouds allows us to suggest in which regions the far-UV radiation stalls in dense gaseous components, and in which ones it escapes and selectively photodissociates the C18O isotope. The non-LTE analysis shows that the molecular gas has very different physical conditions, not only spatially across the cloud, but also along the line of sight. This kind of studies may represent a tool to indirectly estimate (from molecular lines observations) the degree of photodissociation in molecular clouds, which is indeed useful to study the chemistry in the interstellar medium.
Context. G29.96-0.02 is a high-mass star-forming cloud observed at 70, 160, 250, 350, and 500 microns as part of the Herschel survey of the Galactic Plane during the Science Demonstration Phase. Aims. We wish to conduct a far-infrared study of the sources associated with this star-forming region by estimating their physical properties and evolutionary stage, and investigating the clump mass function, the star formation efficiency and rate in the cloud. Methods. We have identified the Hi-GAL sources associated with the cloud, searched for possible counterparts at centimeter and infrared wavelengths, fitted their spectral energy distribution and estimated their physical parameters. Results. A total of 198 sources have been detected in all 5 Hi-GAL bands, 117 of which are associated with 24 microns emission and 87 of which are not associated with 24 microns emission. We called the former sources 24 microns-bright and the latter ones 24 microns-dark. The [70-160] color of the 24 microns-dark sources is smaller than that of the 24 microns-bright ones. The 24 microns-dark sources have lower L_bol and L_bol/M_env than the 24 microns-bright ones for similar M_env, which suggests that they are in an earlier evolutionary phase. The G29-SFR cloud is associated with 10 NVSS sources and with extended centimeter continuum emission well correlated with the 70 microns emission. Most of the NVSS sources appear to be early B or late O-type stars. The most massive and luminous Hi-GAL sources in the cloud are located close to the G29-UC region, which suggests that there is a privileged area for massive star formation towards the center of the G29-SFR cloud. Almost all the Hi-GAL sources have masses well above the Jeans mass but only 5% have masses above the virial mass, which indicates that most of the sources are stable against gravitational collapse. The sources with M_env > M_virial and that ...
We present a new observation of the compact HII region, G29.96-0.02, that allows us to compare the velocity structure in the ionised gas and surrounding molecular gas directly. This allows us to remove most of the remaining ambiguity about the nature of this source. In particular, the comparison of the velocity structure present in the 4S-3P HeI lines with that found in the 1-0 S(1) of molecular hydrogern convincingly rules out a bow shock as being important to the kinematics of this source. Our new observation therefore agrees with our previous conclusion, drawn from a velocity resolved HI Br gamma map, that most of the velocity structure in G29.96-0.02 can largely be explained as a result of a champagne flow model. We also find that the best simple model must invoke a powerful stellar wind to evacuate the `head of the cometary HII region of ionised gas. However, residual differences between model and data tend to indicate that no single simple model can adequately explain all the observed features.
Using the OVRO, Nobeyama, and IRAM mm-arrays, we searched for ``disk-outflow systems in three high-mass (proto)star forming regions: G16.59-0.05, G23.01-0.41, and G28.87+0.07. These were selected from a sample of NH3 cores associated with OH and H2O maser emission and with no or very faint continuum emission. Our imaging of molecular line (including rotational transitions of CH3CN and 3mm dust continuum emission revealed that these are compact, massive, and hot molecular cores (HMCs), that is likely sites of high-mass star formation prior to the appearance of UCHII regions. All three sources turn out to be associated with molecular outflows from CO and/or HCO+ J=1--0 line imaging. In addition, velocity gradients of 10 -- 100 km/s per pc in the innermost densest regions of the G23.01 and G28.87 HMCs are identified along directions roughly perpendicular to the axes of the corresponding outflows. All the results suggest that these cores might be rotating about the outflow axis, although the contribution of rotation to gravitational equilibrium of the HMCs appears to be negligible. Our analysis indicates that the 3 HMCs are close to virial equilibrium due to turbulent pressure support. Comparison with other similar objects where rotating toroids have been identified so far shows that in our case rotation appears to be much less prominent; this can be explained by the combined effect of unfavorable projection, large distance, and limited angular resolution with the current interferometers.
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