Dust Properties of the Dark Cloud IC 5146

C. Kramer, B. Mookerjea, J. S. Richer, C. J. Lada, J. F. Alves

We present the results of a submillimeter dust continuum study of a

molecular ridge in IC 5146 carried out at 850 μm and 450 μm with

SCUBA on the James Clerk Maxell Telescope (JCMT). The mapped region is

˜14'×2.' 5 in size (˜2 pc×0.3 pc) and consists

of at least four dense cores which are likely to be prestellar in

nature. To study the physical properties of the ridge and its embedded

cores, we combined the dust emission data with dust extinction data

obtained by Lada et al. (1999) from the NIR colors of background giant

stars. The ridge shows dust extinctions above ˜10 mag, rising to

up to 40 mag in the cores.


A map of dust temperatures, constructed from the continuum flux ratios,

shows strong temperature gradients: we find temperatures of up to

˜25 K in the outskirts and between the cores, down to less than 10

K in the cores themselves. Several cores appear isothermal, while two

have inwardly decreasing temperatures profiles, which is expected if the

cores are externally heated. Taking into account the derived map of dust

temperature, the resulting map of H2 column densities shows a

strong contrast between the dilute interclump medium and the dense

cores. We used the extinction data to derive in addition a map of the

dust emissivity parametrized by

κ'=κ850/κV. Its average value

corresponds well with the canonical value of Mathis (1990). The

individual cores show significant differences, i.e. κ' varies

between 1×10-5 and ˜7×10-5. We

find an inverse correlation between κ' and Tdust which

we interpret as signature of grain coagulation and the formation of ice

mantles, in accordance with models of dust evolution in dense prestellar

cores (Ossenkopf & Henning 1994, OH94) and the previous detection of

gas-phase depletion of CO (Kramer et al. 1999).

Department of Astrophysics
External organisation(s)
Harvard-Smithsonian Center for Astrophysics, Universität zu Köln, University of Cambridge
Publication date
Austrian Fields of Science 2012
103004 Astrophysics
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