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.

Ammonia in infrared dark clouds

Abstract: Context While low mass clouds have been relatively well studied, our picture of high-mass star formation remains unclear Infrared Dark Clouds appear to be the long sought population of cold and dense aggregations with the potential of harbouring the earliest stages of massive star formation Up to now there has been no systematic study on the temperature distribution, velocity fields, chemical and physical state toward this new cloud populationAims Knowing these properties is crucial for understanding the presence, absence and the very potential of star formation The present paper aims at addressing these questions We analyse temperature structures and velocity fields and gain information on their chemical evolution Methods We mapped the and (2, 2) inversion transitions of ammonia in 9 infrared dark clouds Our observations allow the most reliable determination of gas temperatures in IRDCs to dateResults The gas emission is remarkably coextensive with the extinction seen at infrared wavelengths and with the submillimeter dust emission Our results show that IRDCs are on average cold () and have variations among the different cores IRDC cores are in virial equilibrium, are massive (), highly turbulent (1–3 ) and exhibit significant velocity structure (variations around 1–2 over the cloud) Conclusions We find an increasing trend in temperature from IRDCs with high ammonia column density to high mass protostellar objects and Ultracompact Hii regions, stages of early warm high-mass star formation The linewidths of IRDCs are smaller than those observed in high mass protostellar objects and hot core/Ultracompact Hii regions On basis of this sample, and by comparison of the ammonia gas properties within a cloud and between different clouds, we infer that while active star formation is not yet pervasive in most IRDCs, local condensations might collapse in the future or have already begun forming stars

The Characterization and Galactic Distribution of Infrared Dark Clouds

Abstract: Using 13CO J = 1 ? 0 molecular line emission from the Boston University-Five College Radio Astronomy Observatory Galactic Ring Survey (BU-FCRAO GRS), we have established kinematic distances to 313 infrared dark clouds (IRDCs) by matching the morphology of the molecular line emission in distinct velocity channels to their mid-infrared extinction. The Galactic distribution of IRDCs shows an enhancement toward the Galaxy's most massive and active star-forming structure, the so-called 5 kpc ring. IRDCs have typical sizes of ~5 pc, peak column densities of ~1022 cm-2, LTE masses of ~5 ? 103 M?, and volume-averaged H2 densities of ~2 ? 103 cm-3. The similarity of these properties to those of molecular clumps associated with active star formation suggests that IRDCs represent the densest clumps within giant molecular clouds where clusters may eventually form.

A Catalog of Midcourse Space Experiment Infrared Dark Cloud Candidates

Abstract: We use 8.3 μm mid-infrared images acquired with the Midcourse Space Experiment satellite to identify and catalog infrared dark clouds (IRDCs) in the first and fourth quadrants of the Galactic plane. Because IRDCs are seen as dark extinction features against the diffuse Galactic infrared background, we identify them by first determining a model background from the 8.3 μm images and then searching for regions of high decremental contrast with respect to this background. IRDC candidates in our catalog are defined by contiguous regions bounded by closed contours of a 2 σ decremental contrast threshold. Although most of the identified IRDCs are actual cold dark clouds, some as yet unknown fraction may be spurious identifications. For large high-contrast clouds, we estimate the reliability to be 82%. Low-contrast clouds should have lower reliabilities. Verification of the reality of individual clouds will require additional data. We identify 10,931 candidate IRDCs. For each IRDC, we also catalog cores. These cores, defined as localized regions with at least 40% higher extinction than the cloud's average extinction, are found by iteratively fitting two-dimensional elliptical Gaussian functions to the contrast peaks. We identify 12,774 cores. The catalog contains the position, angular size, orientation, area, peak contrast, peak contrast signal-to-noise, and integrated contrast of the candidate IRDCs and their cores. The distribution of IRDCs closely follows the Galactic diffuse mid-infrared background and peaks toward prominent star-forming regions, spiral arm tangents, and the so-called 5 kpc Galactic molecular ring.

A Catalog of MSX Infrared Dark Cloud Candidates

Abstract: We use 8.3 um mid-infrared images acquired with the Midcourse Space Experiment satellite to identify and catalog Infrared Dark Clouds (IRDCs) in the first and fourth quadrants of the Galactic plane. Because IRDCs are seen as dark extinction features against the diffuse Galactic infrared background, we identify them by first determining a model background from the 8.3 um images and then searching for regions of high decremental contrast with respect to this background. IRDC candidates in our catalog are defined by contiguous regions bounded by closed contours of a 2 sigma decremental contrast threshold. Although most of the identified IRDCs are actual cold, dark clouds, some as yet unknown fraction may be spurious identifications. For large, high contrast clouds, we estimate the reliability to be 82%. Low contrast clouds should have lower reliabilities. Verification of the reality of individual clouds will require additional data. We identify 10,931 candidate infrared dark clouds. For each IRDC, we also catalog cores. These cores, defined as localized regions with at least 40% higher extinction than the cloud's average extinction, are found by iteratively fitting 2-dimensional elliptical Gaussians to the contrast peaks. We identify 12,774 cores. The catalog contains the position, angular size, orientation, area, peak contrast, peak contrast signal-to-noise, and integrated contrast of the candidate IRDCs and their cores. The distribution of IRDCs closely follows the Galactic diffuse mid-infrared background and peaks toward prominent star forming regions, spiral arm tangents, and the so-called 5 kpc Galactic molecular ring.

Hierarchical fragmentation and differential star formation in the Galactic ‘Snake’: infrared dark cloud G11.11−0.12

Abstract: We present Submillimeter Array (SMA) λ = 0.88 and 1.3 mm broad-band observations, and Very Large Array (VLA) observations in NH_3 (J, K) = (1,1) up to (5,5), H_2O and CH_3OH maser lines towards the two most massive molecular clumps in infrared dark cloud (IRDC) G11.11−0.12. Sensitive high-resolution images reveal hierarchical fragmentation in dense molecular gas from the ∼1 pc clump scale down to ∼0.01 pc condensation scale. At each scale, the mass of the fragments is orders of magnitude larger than the Jeans mass. This is common to all four IRDC clumps we studied, suggesting that turbulence plays an important role in the early stages of clustered star formation. Masers, shock heated NH_3 gas, and outflows indicate intense ongoing star formation in some cores while no such signatures are found in others. Furthermore, chemical differentiation may reflect the difference in evolutionary stages among these star formation seeds. We find NH_3 ortho/para ratios of 1.1 ± 0.4, 2.0 ± 0.4, and 3.0 ± 0.7 associated with three outflows, and the ratio tends to increase along the outflows downstream. Our combined SMA and VLA observations of several IRDC clumps present the most in-depth view so far of the early stages prior to the hot core phase, revealing snapshots of physical and chemical properties at various stages along an apparent evolutionary sequence.