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        Cores in infrared dark clouds (IRDCs) seen in the Hi-GAL survey between l=300 degrees and 330 degrees

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        Author
        Wilcock, L.A.
        Ward-Thompson, D.
        Kirk, J.M.
        Stamatellos, D.
        Whitworth, A.
        Elia, D.
        Fuller, G.A.
        DiGiorgio, A.
        Griffin, M.J.
        Molinari, S.
        Martin, P.
        Mottram, J. C.
        Peretto, N.
        Pestalozzi, M.
        Schisano, E.
        Plume, R.
        Smith, H. A.
        Thompson, M. A.
        Attention
        2299/8791
        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-IR (8 mu m) by Spitzer (we refer to these as 'Spitzer-dark' regions). They all lie in the range l = 300-330 degrees and vertical bar b vertical bar <= 1 degrees. Of these, only 1205 were seen in emission in the far-IR (250-500 mu m) 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-IR, but will also be seen in emission in the far-IR at the longest Herschel wavebands (250-500 mu m). If a region is dark at all wavelengths throughout the mid-IR and far-IR, then it is most likely to be simply a region of lower background IR emission (a 'hole in the sky'). Hence, it appears that previous surveys, based on Spitzer and other mid-IR data alone, may have overestimated the total IRDC population by a factor of similar to 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 mu m and found that 972 of them had at least one clearly defined 250-mu m peak, indicating that they contained one or more dense cores. Of these, 653 (67 per cent) contained an 8-mu m point source somewhere within the cloud, 149 (15 per cent) contained a 24-mu m point source but no 8-mu m source and 170 (18 per cent) contained no 24- or 8-mu m point sources. We use these statistics to make inferences about the lifetimes of the various evolutionary stages of IRDCs.
        Publication date
        2012-05
        Published in
        Monthly Notices of the Royal Astronomical Society
        Published version
        https://doi.org/10.1111/j.1365-2966.2012.20680.x
        Other links
        http://hdl.handle.net/2299/8791
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