138 research outputs found
An Overall Picture of the Gas Flow in a Massive Cluster-forming Region: The Case of G10. 6–0.4
No full textThe Decrease of Specific Angular Momentum and the Hot Toroid Formation: The Massive Clump G10.6–0.4
No full textVERY LARGE ARRAY OBSERVATIONS OF AMMONIA IN HIGH-MASS STAR FORMATION REGIONS
No full textWe report systematic mapping observations of the NH3 (1, 1) and (2, 2) inversion lines toward 62 high-mass star-forming regions using the Very Large Array (VLA) in its D and DnC array configurations. The VLA images cover a spatial dynamic range from 40'' to 3'', allowing us to trace gas kinematics from similar to 1 pc scales to less than or similar to 0.1 pc scales. Based on the NH3 morphology and the infrared nebulosity on 1 pc scales, we categorize three subclasses in the sample: filaments, hot cores, and NH3-dispersed sources. The ubiquitous gas filaments found on 1 pc scales have a typical width of similar to 0.1 pc and often contain regularly spaced fragments along the major axis. The spacing of the fragments and the column densities is consistent with the turbulent supported fragmentation of cylinders. Several sources show multiple filaments that converge toward a center where the velocity field in the filaments is consistent with gas flows. We derive rotational temperature maps for the entire sample. For the three hot core sources, we find a projected radial temperature distribution that is best fit by power-law indices from -0.18 to -0.35. We identify 174 velocity-coherent similar to 0.1 pc scale dense cores from the entire sample. The mean physical properties for these cores are 1.1 km s(-1) in intrinsic linewidth, 18 K in NH3 rotational temperature, 2.3 x 10(15) cm(-2) in NH3 gas column density, and 67M(circle dot) in molecular mass. The dense cores identified from the filamentary sources are closer to being virialized. Dense cores in the other two categories of sources appear to be dynamically unstable
Molecular Spectral Lines In Filamentary Infrared Dark Clouds
Get PDFMany infrared dark clouds (IRDCs) in our Galaxy have filamentary structures, and some of them present converging filaments to a central hub, known as hub-filament systems (HFSs). These filaments could play a crucial role in feeding gas to the star forming regions at the hub. We analyzed NH (J,K)=(1,1) and (2,2) spectral lines data obtained with the Very Large Array (VLA) towards five filamentary IRDCs, and derived the gas temperature based on the line ratios. Furthermore, with the Submillimeter Array (SMA) in the compact and sub-compact configurations, we obtained dust emission and spectra lines at 1.3 mm towards these sources. We found filamentary structures in both dust continuum and spectral line emission, with a characteristic width of 0.1 pc and length of 1 pc. The dust emission is consistent with the infrared extinction features, indicating the existence of dense and cold gas, while massive dust cores are usually associated with the hubs. Complex organic molecules including CHOH are found towards the dust cores. In particular, optically-thin intermediate density gas tracers, such as CO, reveal a possible trend of gas infall along filaments towards hubs. This is consistent with the scenario that dense gas is accreted onto dense cores through filaments and form high-mass star clusters.Made available in DSpace on 2014-09-17T16:55:16Z (GMT). No. of bitstreams: 3
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Previous issue date: 2014-06-17Made available in DSpace on 2015-04-14T18:40:34Z (GMT). No. of bitstreams: 4
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Previous issue date: 2014-06-1
Interpreting observations of edge-on gravitationally unstable accretion flows
No full textContext. Gravitational collapse of molecular cloud or cloud core/clump
may lead to the formation of geometrically flattened, rotating accretion flow surrounding
the new born star or star cluster. Gravitational instability may occur in such accretion
flow when the gas to stellar mass ratio is high (e.g., over ~10%).
Aims. This paper takes the OB cluster-forming region G10.6-0.4 as an
example. We introduce the enclosed gas mass around its central ultra compact (UC) Hi
Investigating Fragmentation of Gas Structures in OB Cluster-forming Molecular Clump G33.92+0.11 with 1000 au Resolution Observations of ALMA
No full textWe report new similar to 1000 au spatial resolution observations of 225 GHz dust continuum emission toward the OB cluster-forming molecular clump G33.92+0.11. On parsec scales, this molecular clump presents a morphology with several arm-like dense gas structures surrounding the two central massive (greater than or similar to 100 M-circle dot) cores. From the new higher resolution observations, we identified 28 localized, spatially compact dust continuum emission sources, which may be candidates of young stellar objects (YSOs). Only one of them is not embedded within known armlike (or elongated) dense gas structures. The spatial separations of these compact sources can be very well explained by Jeans lengths. We found that G33.92+0.11 may be consistently described by a marginally centrifugally supported, Toomre unstable accretion flow that is approximately in a face-on projection. The arm-like overdensities are a natural consequence of the Toomre instability, which can fragment to form YSOs in shorter timescales than the timescale of the global clump contraction. On our resolved spatial scales, there is no evidence yet that the fragmentation is halted by turbulence, the magnetic field, or stellar feedback
An ALMA sub-arcsecond view of molecular gas in massive star-forming region G10.6-0.4
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Previous issue date: 2019-06-19Made available in DSpace on 2020-01-25T19:30:45Z (GMT). No. of bitstreams: 4
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Previous issue date: 2019-06-19While massive star-forming regions are known to exhibit an extremely rich and diverse chemistry, few such sources have been mapped at high spatial resolution. Since the chemical structure of these sources displays substantial spatial variation among species on small scales (~AU), high spatial resolution observations are needed to constrain chemical evolution models of massive star formation. We will present new ALMA 1.3 mm observations toward massive OB cluster-forming region G10.6-0.4 at a resolution of 0.12 (600 AU). While the kinematics of G10.6 have been extensively studied at centimeter wavelengths, sensitive and high angular resolution observations in the millimeter and submillimeter regime have been lacking. Given the high sensitivity and bandwidth of our ALMA observations, we are able to derive rotational temperature and column density maps toward the central 8 by 8 region of G10.6 for over 10 different species, including traditional warm gas tracers such as CHCN, shock tracers HNCO and SiO, and a variety of complex organic molecules. Combined with our simultaneous observations of ionized gas in hydrogen recombination lines, our exquisite spatial resolution allows us to constrain the chemical influences of massive stellar feedback in the form of highly structured and inhomogeneous molecular emission, prominent spatial anti-correlations between molecular and ionized gas, and order-of-magnitude variations in physical gas conditions
Combined VLA+GBT data of NH3 (1,1) and (2,2) in Orion A OMC1
No full textdata files of combined GBT and VLA observations of the Orion A OMC1 region, first presented in the paper 'Dense gas kinematics and a narrow filament in the Orion A OMC1 region using NH3', first presented in ApJ 861, 77 (https://arxiv.org/abs/1806.01847
Peculiar Disk Substructures Associated with the Young Eruptive Star EX Lupi
No full textYoung eruptive stars such as EXors undergo dramatic accretion outbursts characterized by sudden optical brightenings, yet the underlying physical mechanism remains uncertain. We present high-resolution Atacama Large Millimeter/submillimeter Array (ALMA) Band 3 and 4 continuum observations of EX Lupi, the prototypical EXor-type variable, reconstructed using super-resolution imaging with sparse modeling. Our images reveal, for the first time, two distinct substructures: a compact, crescent-shaped inner arc within 10 au of the star, and a narrow outer ring at 30 au. The inner arc is strongly elongated and casts a shadow observed in Very Large Telescope/SPHERE near-infrared scattered light. The outer ring exhibits a radial width comparable to the local pressure scale height, consistent with moderately efficient dust trapping. Geometric and thermal analysis of the disk surface, based on combined ALMA and SPHERE data, indicates that the disk is moderately flared with an average disk temperature consistent with that of classical T Tauri disks. The observed substructures suggest dynamical perturbations—plausibly induced by a massive companion—that may modulate accretion rates through gravitational interaction with the inner arc. These findings provide morphological evidence linking disk substructure to episodic accretion in the structurally mature disk
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