Showing papers on "Infrared dark cloud published in 2017"

The TOP-SCOPE survey of Planck Galactic Cold Clumps: Survey overview and results of an exemplar source, PGCC G26.53+0.17

Abstract: The low dust temperatures (<14 K) of Planck Galactic Cold Clumps (PGCCs) make them ideal targets to probe the initial conditions and very early phase of star formation. TOP-SCOPE is a joint survey program targeting ~2000 PGCCs in J=1-0 transitions of CO isotopologues and ~1000 PGCCs in 850 micron continuum emisison. The objective of the TOP-SCOPE survey and the joint surveys (SMT 10-m, KVN 21-m and NRO 45-m) is to statistically study the initial conditions occurring during star formation and the evolution of molecular clouds, across a wide range of environments. The observations, data analysis and example science cases for these surveys are introduced with an exemplar source, PGCC G26.53+0.17 (G26), which is a filamentary infrared dark cloud (IRDC). The total mass, the length and the mean line-mass (M/L) of the G26 filament are ~6200 Msun, ~12 pc and ~500 Msun/pc, respectively. Ten massive clumps including eight starless ones are found along the filament. The most massive Clump as a whole may be still in global collapse while its denser part seems to be undergoing expansion due to outflow feedback. The fragmentation in G26 filament from cloud scale to clump scale is in agreement with gravitational fragmentation of an isothermal, non-magnetized, and turbulent supported cylinder. A bimodal behavior in dust emissivity spectral index ($\beta$) distribution is found in G26, suggesting grain growth along the filament. The G26 filament may be formed due to large-scale compression flows evidenced by the temperature and velocity gradients across its natal cloud.

Distribution of water in the G327.3-0.6 massive star-forming region

Abstract: Aims: Following our past study of the distribution of warm gas in the G327.3-0.6 massive star-forming region, we aim here at characterizing the large-scale distribution of water in this active region of massive star formation made of individual objects in different evolutionary phases. We investigate possible variations of the water abundance as a function of evolution. Methods: We present Herschel/PACS (4'× 4') continuum maps at 89 and179 μm encompassing the whole region (Hii region and the infrared dark cloud, IRDC) and an APEX/SABOCA (2'× 2') map at 350 μm of the IRDC. New spectral Herschel/HIFI maps toward the IRDC region covering the low-energy water lines at 987 and 1113 GHz (and their H218O counterparts) are also presented and combined with HIFI pointed observations toward the G327 hot core region. We infer the physical properties of the gas through optical depth analysis and radiative transfer modeling of the HIFI lines. Results: The distribution of the continuum emission at 89 and 179 μm follows the thermal continuum emission observed at longer wavelengths, with a peak at the position of the hot core and a secondary peak in the Hii region, and an arch-like layer of hot gas west of this Hii region. The same morphology is observed in the p-H2O 111-000 line, in absorption toward all submillimeter dust condensations. Optical depths of approximately 80 and 15 are estimated and correspond to column densities of 1015 and 2 × 1014 cm-2, respectively, for the hot core and IRDC position. These values indicate an abundance of water relative to H2 of 3 × 10-8 toward the hot core, while the abundance of water does not change along the IRDC with values close to some 10-8. Infall (over at least 20″) is detected toward the hot core position with a rate of 1-1.3 × 10-2M⊙ /yr, high enough to overcome the radiation pressure that is due to the stellar luminosity. The source structure of the hot core region appears complex, with a cold outer gas envelope in expansion, situated between the outflow and the observer, extending over 0.32 pc. The outflow is seen face-on and rather centered away from the hot core. Conclusions: The distribution of water along the IRDC is roughly constant with an abundance peak in the more evolved object, that is, in the hot core. These water abundances are in agreement with previous studies in other massive objects and chemical models. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

Probing the massive star forming environment - a multiwavelength investigation of the filamentary IRDC G333.73+0.37

Abstract: We present a multiwavelength study of the filamentary infrared dark cloud (IRDC) G333.73+0.37. The region contains two distinct mid-infrared sources S1 and S2 connected by dark lanes of gas and dust. Cold dust emission from the IRDC is detected at seven wavelength bands and we have identified 10 high density clumps in the region. The physical properties of the clumps such as temperature: 14.3-22.3 K and mass: 87-1530 M_sun are determined by fitting a modified blackbody to the spectral energy distribution of each clump between 160 micron and 1.2 mm. The total mass of the IRDC is estimated to be $~4700 M_sun. The molecular line emission towards S1 reveals signatures of protostellar activity. Low frequency radio emission at 1300 and 610 MHz is detected towards S1 (shell-like) and S2 (compact morphology), confirming the presence of newly formed massive stars in the IRDC. Photometric analysis of near and mid-infrared point sources unveil the young stellar object population associated with the cloud. Fragmentation analysis indicates that the filament is supercritical. We observe a velocity gradient along the filament, that is likely to be associated with accretion flows within the filament rather than rotation. Based on various age estimates obtained for objects in different evolutionary stages, we attempt to set a limit to the current age of this cloud.

Gas emission and dynamics in the infrared dark cloud G31.23+0.05

Abstract: We performed a multiwavelength study towards the infrared dark cloud (IRDC) G31.23+0.05 with new CO observations from Purple Mountain Observatory and archival data (the GLIMPSE, MIPSGAL, HERSCHEL, ATLASGAL, BGPS and NVSS surveys). From these observations, we identified three IRDCs with systemic velocities of 108.36 ± 0.06 (cloud A), 104.22 ± 0.11 (cloud B) and 75.73 ± 0.07 km s −1 (cloud C) in the line of sight towards IRDC G31.23. Analyses of the molecular and dust emission suggest that cloud A is a filamentary structure containing a young stellar object; clouds B and C both include a starless core. Clouds A and B are gravitationally bound and have a chance to form stars. In addition, the velocity information and the position-velocity diagram suggest that clouds A and B are adjacent in space and provide a clue hinting at a possible cloud-cloud collision. Additionally, the distribution of dust temperature shows a temperature bubble. The compact core in cloud A is associated with an UCHII region, an IRAS source, H 2 O masers, CH 3 OH masers and OH masers, suggesting that massive star formation is active there. We estimate the age of the HII region to be (0.03–0.09) Myr, indicating that the star inside is young.