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.

Submillimeter observations of dense clumps in the infrared dark cloud g049.40-00.01

Abstract: We obtained 350 and 850 μm continuum maps of the infrared dark cloud G049.40-00.01. Twenty-one dense clumps were identified within G049.40-00.01 based on the 350 μm continuum map with an angular resolution of about 9".6. We present submillimeter continuum maps and report physical properties of the clumps. The masses of clumps range from 50 to 600 M_☉. About 70% of the clumps are associated with bright 24 μm emission sources, and they may contain protostars. The two most massive clumps show extended, enhanced 4.5 μm emission indicating vigorous star-forming activity. The clump-size-mass distribution suggests that many of them are forming high-mass stars. G049.40-00.01 contains numerous objects in various evolutionary stages of star formation, from pre-protostellar clumps to H II regions.

Distributed Low-Mass Star Formation in the IRDC G34.43+00.24

Abstract: We have used deep near-infrared observations with adaptive optics to discover a distributed population of low-mass protostars within the filamentary Infrared Dark Cloud G34.43+00.24. We use maps of dust emission at multiple wavelengths to determine the column density structure of the cloud. In combination with an empirically-verified model of the magnitude distribution of background stars, this column density map allows us to reliably determine overdensities of red sources that are due to embedded protostars in the cloud. We also identify protostars through their extended emission in K-band which comes from excited H2 in protostellar outflows or reflection nebulosity. We find a population of distributed low-mass protostars, suggesting that low-mass protostars may form earlier than, or contemporaneously with, high-mass protostars in such a filament. The low-mass protostellar population may also produce the narrow linewidth SiO emission observed in some clouds without high-mass protostars. Finally, we use a molecular line map of the cloud to determine the virial parameter per unit length along the filament and find that the highest mass protostars form in the most bound portion of the filament, as suggested by theoretical models.

ALMA–IRDC – II. First high-angular resolution measurements of the 14N/15N ratio in a large sample of infrared-dark cloud cores

Abstract: The 14N/15N ratio in molecules exhibits a large variation in star-forming regions, especially when measured from N2H+ isotopologues. However, there are only a few studies performed at high-angular resolution. We present the first interferometric survey of the 14N/15N ratio in N2H+ obtained with the Atacama Large Millimeter Array towards four infrared-dark clouds harbouring 3~mm continuum cores associated with different physical properties. We detect N15NH+ (1-0) in about 20-40% of the cores, depending on the host cloud. The 14N/15N values measured towards the millimeter continuum cores range from a minimum of 80 up to a maximum of 400. The spread of values is narrower than that found in any previous single-dish survey of high-mass star-forming regions, and than that obtained using the total power data only. This suggests that the 14N/15N ratio is on average higher in the diffuse gaseous envelope of the cores, and stresses the need for high-angular resolution maps to measure correctly the 14N/15N ratio in dense cores embedded in IRDCs. The average 14N/15N ratio of 210 is also lower than the interstellar value at the Galactocentric distance of the clouds (300-330), although the sensitivity of our observations does not allow us to unveil 14N/15N ratios higher than 400. No clear trend is found between the 14N/15N ratio and the core physical properties. We find only a tentative positive trend between 14N/15N and the H2 column density. However, firmer conclusions can be drawn only with higher sensitivity measurements.

Maser Emission toward the Infrared Dark Cloud G359.94+0.17 Seen in Silhouette against the Galactic Center

Abstract: The infrared dark cloud G359.94+0.17 is a conspicuous, opaque cloud, which is seen in silhouette against the Galactic center. We found unexpectedly strong (� 50 Jy) maser emission of CH3OH at 44 GHz with additional weak 22 GHz H2O maser and 43 GHz SiO thermal emissions toward this cloud. Detections of these molecular lines indicate that strong star-forming activities are proceeding in this cloud, which was not reported previously despite of numerous studies toward the Galactic center. The line profiles of the NH3 inversion lines at 23 GHz indicate that G359.94+0.17 is composed of mainly two clouds with Vlsr = 0, and 15 km s � 1 overlapped on the line of sight. The maser emission is associated with the 15 km s � 1 cloud, suggesting that it is located at the Norma spiral arm.

Deuterium Fractionation as an Evolutionary Probe in the Infrared Dark Cloud G28.34+0.06

Abstract: We have observed the J=3-2 transition of N2H+ and N2D+ to investigate the trend of deuterium fractionation with evolutionary stage in three selected regions in the Infrared Dark Cloud (IRDC) G28.34+0.06 with the Submillimeter Telescope (SMT) and the Submillimeter Array (SMA). A comprehensible enhancement of roughly 3 orders of magnitude in deuterium fractionation over the local interstellar D/H ratio is observed in all sources. In particular, our sample of massive star-forming cores in G28.34+0.06 shows a moderate decreasing trend over a factor of 3 in the N(N2D+)/N(N2H+) ratio with evolutionary stage, a behavior resembling what previously found in low-mass protostellar cores. This suggests a possible extension for the use of the N(N2D+)/N(N2H+) ratio as an evolutionary tracer to high-mass protostellar candidates. In the most evolved core, MM1, the N2H+ (3-2) emission appears to avoid the warm region traced by dust continuum emission and emission of 13CO sublimated from grain mantles, indicating an instant release of gas-phase CO. The majority of the N2H+ and N2D+ emission is associated with extended structures larger than 8" (~ 0.2 pc).