970 research outputs found

    A multi-wavelength observation and investigation of six infrared dark clouds

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    Context. Infrared dark clouds (IRDCs) are ubiquitous in the Milky Way, yet they play a crucial role in breeding newly-formed stars. Aims. With the aim of further understanding the dynamics, chemistry, and evolution of IRDCs, we carried out multi-wavelength observations on a small sample. Methods. We performed new observations with the IRAM 30 m and CSO 10.4 m telescopes, with tracers HCO+{\rm HCO^+}, HCN, N2H+{\rm N_2H^+}, C18O{\rm C^{18}O}, DCO+^+, SiO, and DCN toward six IRDCs G031.97+00.07, G033.69-00.01, G034.43+00.24, G035.39-00.33, G038.95-00.47, and G053.11+00.05. Results. We investigated 44 cores including 37 cores reported in previous work and seven newly-identified cores. Toward the dense cores, we detected 6 DCO+^+, and 5 DCN lines. Using pixel-by-pixel spectral energy distribution (SED) fits of the Herschel\textit{Herschel} 70 to 500 μ\mum, we obtained dust temperature and column density distributions of the IRDCs. We found that N2H+{\rm N_2H^+} emission has a strong correlation with the dust temperature and column density distributions, while C18O{\rm C^{18}O} showed the weakest correlation. It is suggested that N2H+{\rm N_2H^+} is indeed a good tracer in very dense conditions, but C18O{\rm C^{18}O} is an unreliable one, as it has a relatively low critical density and is vulnerable to freezing-out onto the surface of cold dust grains. The dynamics within IRDCs are active, with infall, outflow, and collapse; the spectra are abundant especially in deuterium species. Conclusions. We observe many blueshifted and redshifted profiles, respectively, with HCO+{\rm HCO^+} and C18O{\rm C^{18}O} toward the same core. This case can be well explained by model "envelope expansion with core collapse (EECC)".Comment: 24 pages, 11 figures, 4 tables. To be published in A&A. The resolutions of the pictures are cut dow

    Probing the initial conditions of high-mass star formation -- IV. Gas dynamics and NH2_2D chemistry in high-mass precluster and protocluster clumps

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    The initial stage of star formation is a complex area study because of its high density and low temperature. Under such conditions, many molecules become depleted from the gas phase by freezing out onto dust grains. However, the deuterated species could remain gaseous and are thus ideal tracers. We investigate the gas dynamics and NH2_2D chemistry in eight massive pre/protocluster clumps. We present NH2_2D 111_{11}-101_{01} (at 85.926 GHz), NH3_3 (1, 1) and (2, 2) observations in the eight clumps using the PdBI and the VLA, respectively. We find that the distribution between deuterium fractionation and kinetic temperature shows a number density peak at around Tkin=16.1T_{\rm kin}=16.1 K, and the NH2_2D cores are mainly located at a temperature range of 13.0 to 22.0 K. We detect seven instances of extremely high deuterium fractionation of 1.0Dfrac1.411.0 \leqslant D_{\rm frac} \leqslant 1.41. We find that the NH2_2D emission does not appear to coincide exactly with either dust continuum or NH3_3 peak positions, but often surrounds the star-formation active regions. This suggests that the NH2_{2}D has been destroyed by the central young stellar object (YSO) due to its heating. The detected NH2_2D lines are very narrow with a median width of 0.98±0.02km/s\rm 0.98\pm0.02 km/s. The extracted NH2_2D cores are gravitationally bound (αvir<1\alpha_{\rm vir} < 1), are likely prestellar or starless, and can potentially form intermediate-mass or high-mass stars. Using NH3_3 (1, 1) as a dynamical tracer, we find very complicated dynamical movement, which can be explained by a combined process with outflow, rotation, convergent flow, collision, large velocity gradient, and rotating toroids. High deuterium fractionation strongly depends on the temperature condition. NH2_2D is a poor evolutionary indicator of high-mass star formation in evolved stages, but a useful tracer in the starless and prestellar cores.Comment: 27 pages, 25 figures, 6 tables, accepted for publication in A&

    Gas kinematics and star formation in the filamentary molecular cloud G47.06+0.26

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    We performed a multi-wavelength study toward the filamentary cloud G47.06+0.26 to investigate the gas kinematics and star formation. We present the 12CO (J=1-0), 13CO (J=1-0) and C18O (J=1-0) observations of G47.06+0.26 obtained with the Purple Mountain Observation (PMO) 13.7 m radio telescope to investigate the detailed kinematics of the filament. The 12CO (J=1-0) and 13CO (J=1-0) emission of G47.06+0.26 appear to show a filamentary structure. The filament extends about 45 arcmin (58.1 pc) along the east-west direction. The mean width is about 6.8 pc, as traced by the 13CO (J=1-0) emission. G47.06+0.26 has a linear mass density of about 361.5 Msun/pc. The external pressure (due to neighboring bubbles and H II regions) may help preventing the filament from dispersing under the effects of turbulence. From the velocity-field map, we discern a velocity gradient perpendicular to G47.06+0.26. From the Bolocam Galactic Plane Survey (BGPS) catalog, we found nine BGPS sources in G47.06+0.26, that appear to these sources have sufficient mass to form massive stars. We obtained that the clump formation efficiency (CFE) is about 18% in the filament. Four infrared bubbles were found to be located in, and adjacent to, G47.06+0.26. Particularly, infrared bubble N98 shows a cometary structure. CO molecular gas adjacent to N98 also shows a very intense emission. H II regions associated with infrared bubbles can inject the energy to surrounding gas. We calculated the kinetic energy, ionization energy, and thermal energy of two H II regions in G47.06+0.26. From the GLIMPSE I catalog, we selected some Class I sources with an age of about 100000 yr, which are clustered along the filament. The feedback from the H II regions may cause the formation of a new generation of stars in filament G47.06+0.26.Comment: 10 pages, 11 figures, accepted for publication in A&
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