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arXiv · 1202.0395

Cores in Infra-Red Dark Clouds (IRDCs) seen in the Hi-GAL survey between l = 300° and l = 330°

L. A. Wilcock·D. Ward-Thompson·J. M. Kirk·D. Stamatellos·A. Whitworth·D. Elia·G. A. Fuller·A. DiGiorgio·M. J. Griffin·S. Molinari·P. Martin·J. C. Mottram·N. Peretto·M. Pestalozzi·E. Schisano·R. Plume·H. A. Smith·M. A. Thompson
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Abstract

We have used data taken as part of the Herschel infrared Galactic Plane survey (Hi-GAL) to study 3171 infrared-dark cloud (IRDC) candidates that were identified in the mid-infrared (8 μm) by Spitzer (we refer to these as 'Spitzer-dark' regions). They all lie in the range l=300 - 330 \circ and |b| 6 1 \circ. Of these, only 1205 were seen in emission in the far-infrared (250-500 μm) by Herschel (we call these 'Herschel-bright' clouds). It is predicted that a dense cloud will not only be seen in absorption in the mid-infrared, but will also be seen in emission in the far-infrared at the longest Herschel wavebands (250-500 μm). If a region is dark at all wavelengths throughout the mid-infrared and far-infrared, then it is most likely to be simply a region of lower background infrared emission (a 'hole in the sky'). Hence, it appears that previous surveys, based on Spitzer and other mid-infrared data alone, may have over-estimated the total IRDC population by a factor of 2. This has implications for estimates of the star formation rate in IRDCs in the Galaxy.We studied the 1205 Herschel-bright IRDCs at 250 μm, and found that 972 of them had at least one clearly defined 250-μm peak, indicating that they contained one or more dense cores. Of these, 653 (67 per cent) contained an 8-μm point source somewhere within the cloud, 149 (15 per cent) contained a 24-μm point source but no 8-μm source, and 170 (18 per cent) contained no 24-μm or 8-μm point sources. We use these statistics to make inferences about the lifetimes of the various evolutionary stages of IRDCs.

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L. A. Wilcock, D. Ward-Thompson, J. M. Kirk, D. Stamatellos, A. Whitworth, D. Elia, G. A. Fuller, A. DiGiorgio, M. J. Griffin, S. Molinari, P. Martin, J. C. Mottram, N. Peretto, M. Pestalozzi, E. Schisano, R. Plume, H. A. Smith, M. A. Thompson. 2012-02-02. Cores in Infra-Red Dark Clouds (IRDCs) seen in the Hi-GAL survey between l = 300° and l = 330°. https://doi.org/10.1111/j.1365-2966.2012.20680.x

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