Infrared dark cloud

About: Infrared dark cloud is a research topic. Over the lifetime, 232 publications have been published within this topic receiving 13800 citations.

Unveiling a network of parallel filaments in the infrared dark cloud g14.225–0.506

Abstract: We present the results of combined NH_3 (1,1) and (2,2) line emission observed with the Very Large Array and the Effelsberg 100 m telescope of the infrared dark cloud G14225–0506 The NH3 emission reveals a network of filaments constituting two hub-filament systems Hubs are associated with gas of rotational temperature T_(rot) ~ 15 K, non-thermal velocity dispersion σ_(NT) ~ 1 km s^(–1), and exhibit signs of star formation, while filaments appear to be more quiescent (T_(rot) ~ 11 K and σ_(NT) ~ 06 km s^(–1)) Filaments are parallel in projection and distributed mainly along two directions, at PA ~ 10° and 60°, and appear to be coherent in velocity The averaged projected separation between adjacent filaments is between 05 pc and 1 pc, and the mean width of filaments is 012 pc Cores within filaments are separated by ~033 ± 009 pc, which is consistent with the predicted fragmentation of an isothermal gas cylinder due to the "sausage"-type instability The network of parallel filaments observed in G14225–0506 is consistent with the gravitational instability of a thin gas layer threaded by magnetic fields Overall, our data suggest that magnetic fields might play an important role in the alignment of filaments, and polarization measurements in the entire cloud would lend further support to this scenario

The seeds of star formation in the filamentary infrared-dark cloud G011.11-0.12

Abstract: Context. Infrared-dark clouds (IRDCs) are the precursors to massive stars and stellar clusters. G011.11–0.12 is a well-studied filamentary IRDC, though, to date, the absence of far-infrared data with sufficient spatial resolution has limited the understanding of the structure and star-formation activity. Aims. We use Herschel to study the embedded population of young pre- and protostellar cores in this IRDC. Methods. We examine the cloud structure, which appears in absorption at short wavelength and in emission at longer wavelength. We derive the properties of the massive cores from the spectral energy distributions of bright far-infrared point sources detected with the PACS instrument aboard Herschel. Results. We report on the detection and characterization of pre- and protostellar cores in a massive filamentary infrared-dark cloud G011.11–0.12 using PACS. We characterize 18 cores directly associated with the filament, two of which have masses over 50 M� , making them the best candidates to become massive stars in G011.11−0.12. These cores are likely at various stages of protostar formation, showing elevated temperature (� T �∼ 22 K) with respect to the ambient gas reservoir. The core masses (� M �∼ 24 M� )a re small compared to that in the cold filament. The mean core separation is 0.9 pc, well in excess of the Jeans length in the filament. Conclusions. We confirm that star formation in IRDCs is underway and diverse, and IRDCs have the capability of forming massive stars and clusters.

The dynamical properties of dense filaments in the infrared dark cloud G035.39−00.33⋆

Abstract: Infrared Dark Clouds (IRDCs) are unique laboratories to study the initial conditions of high-mass star and star cluster formation. We present high-sensitivity and high-angular resolution IRAM PdBI observations of N2H+ (1-0) towards IRDC G035.39-00.33. It is found that G035.39-00.33 is a highly complex environment, consisting of several mildly supersonic filaments (sigma_NT/c_s ~1.5), separated in velocity by <1 km s^-1 . Where multiple spectral components are evident, moment analysis overestimates the non-thermal contribution to the line-width by a factor ~2. Large-scale velocity gradients evident in previous single-dish maps may be explained by the presence of substructure now evident in the interferometric maps. Whilst global velocity gradients are small (<0.7 km s^-1 pc^-1), there is evidence for dynamic processes on local scales (~1.5-2.5 km s^-1 pc^-1 ). Systematic trends in velocity gradient are observed towards several continuum peaks. This suggests that the kinematics are influenced by dense (and in some cases, starless) cores. These trends are interpreted as either infalling material, with accretion rates ~(7 \pm 4)x10^-5 M_sun yr^-1 , or expanding shells with momentum ~24 \pm 12 M_sun km s^-1 . These observations highlight the importance of high-sensitivity and high-spectral resolution data in disentangling the complex kinematic and physical structure of massive star forming regions.

Parsec-scale SiO emission in an infrared dark cloud

Abstract: We present high-sensitivity 2 × 4a rcmin 2 maps of the J = 2→1 rotational lines of SiO, CO, 13 CO and C 18 O, observed towards the filamentary infrared dark cloud (IRDC) G035.39−00.33. Single-pointing spectra of the SiO J = 2→1 and J = 3→2 lines towards several regions in the filament are also reported. The SiO images reveal that SiO is widespread along the IRDC (size ≥2 pc), showing two different components: one bright and compact arising from three condensations (N, E and S) and the other weak and extended along the filament. While the first component shows broad lines (linewidths of ∼4–7 km s −1 ) in both SiO J = 2→1 and SiO J = 3→2, the second one is only detected in SiO J = 2→1 and has narrow lines (∼0.8 km s −1 ). The maps of CO and its isotopologues show that low-density filaments are intersecting the IRDC and appear to merge towards the densest portion of the cloud. This resembles the molecular structures predicted by flow-driven, shock-induced and magneticallyregulated cloud formation models. As in outflows associated with low-mass star formation, the excitation temperatures and fractional abundances of SiO towards N, E and S increase with velocity from ∼ 6t o 40 Ka nd from∼10 −10 to ≥10 −8 , respectively, over a velocity range of ∼ 7k m s −1 . Since 8 μm and 24 μm sources and/or extended 4.5 μm emission are detected in N, E and S, broad SiO is likely produced in outflows associated with high-mass protostars. The excitation temperatures and fractional abundances of the narrow SiO lines, however, are very low (∼9 K and ∼10 −11 , respectively), and consistent with the processing of interstellar grains by the passage of a shock with vs ∼ 12 km s −1 . This emission could be generated (i) by a large-scale shock, perhaps remnant of the IRDC formation process, (ii) by decelerated or recently processed gas in large-scale outflows driven by 8- and 24-μm sources or (iii) by an undetected and widespread population of lower mass protostars. High-angular-resolution observations are needed to disentangle between these three scenarios.

The "Nessie" Nebula: Cluster Formation in a Filamentary Infrared Dark Cloud

Abstract: The "Nessie" Nebula is a filamentary infrared dark cloud (IRDC) with a large aspect ratio of over 150:1 (15 × 001 or 80 pc × 0.5 pc at a kinematic distance of 3.1 kpc). Maps of HNC (1-0) emission, a tracer of dense molecular gas, made with the Australia Telescope National Facility Mopra telescope, show an excellent morphological match to the mid-IR extinction. Moreover, because the molecular line emission from the entire nebula has the same radial velocity to within ±3.4 km s–1, the nebula is a single, coherent cloud and not the chance alignment of multiple unrelated clouds along the line of sight. The Nessie Nebula contains a number of compact, dense molecular cores which have a characteristic projected spacing of ~4.5 pc along the filament. The theory of gravitationally bound gaseous cylinders predicts the existence of such cores, which, due to the "sausage" or "varicose" fluid instability, fragment from the cylinder at a characteristic length scale. If turbulent pressure dominates over thermal pressure in Nessie, then the observed core spacing matches theoretical predictions. We speculate that the formation of high-mass stars and massive star clusters arises from the fragmentation of filamentary IRDCs caused by the "sausage" fluid instability that leads to the formation of massive, dense molecular cores. The filamentary molecular gas clouds often found near high-mass star-forming regions (e.g., Orion, NGC 6334, etc.) may represent a later stage of IRDC evolution.