Infrared Dark Clouds and high-mass star formation activity in Galactic Molecular Clouds

Abstract

Ever since their discovery, Infrared dark clouds (IRDCs) are generally considered to be the sites just at the onset of high-mass (HM) star formation. In recent years, it has been realized that not all IRDCs harbour HM Young Stellar Objects (YSOs). Only those IRDCs satisfying a certain mass-size criterion, or equivalently above a certain threshold density, are found to contain HMYSOs. In all cases, IRDCs provide ideal conditions for the formation of stellar clusters. In this paper, we study the massive stellar content of IRDCs to re-address the relation between IRDCs and HM star formation. For this purpose, we have identified all IRDCs associated to a sample of 12 Galactic molecular clouds (MCs). The selected MCs have been the target of a systematic search for YSOs in an earlier study. The catalogued positions of YSOs have been used to search all YSOs embedded in each identified IRDC. In total, we have found 834 YSOs in 128 IRDCs. The sample of IRDCs have mean surface densities of 319 Mo/pc2, mean mass of 1062 Mo, and a mass function power-law slope -1.8, which are similar to the corresponding properties for the full sample of IRDCs and resulting physical properties in previous studies. We find that all those IRDCs containing at least one intermediate to high-mass young star satisfy the often-used mass-size criterion for forming HM stars. However, not all IRDCs satisfying the mass-size criterion contain HM stars. We find that the often used mass-size criterion corresponds to 35% probability of an IRDC forming a massive star. Twenty five (20%) of the IRDCs are potential sites of stellar clusters of mass more than 100 Mo.

9 pages. Accepted for publication in ApJ

References in corpus (5)

• The Boston University-Five College Radio Astronomy Observatory Galactic Ring Survey
• A Minimum Column Density of 1 g cm^-2 for Massive Star Formation
• Kinematic Distances to Molecular Clouds identified in the Galactic Ring Survey
• The dynamical properties of dense filaments in the infrared dark cloud G035.39-00.33
• The identification of filaments on far infrared and submillimiter images. Morphology, physical conditions and relation with star formation of filamentary structure

Cited by in corpus (2)

• Dense cores in the Seahorse infrared dark cloud: physical properties from modified blackbody fits to the far-infrared-submillimetre spectral energy distributions
• Investigating star-formation activity towards the southern HII region RCW 42