Dust properties of the dark cloud IC 5146. Submillimeter and NIR imaging

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

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

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

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

~ 14'x2farcm5 in size ( ~ 2 pcx0.3 pc) and consists of at least four

dense cores which are likely to be prestellar in nature. To study the

dust 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 up to 35 mag in the cores.


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

shows significant temperature gradients: we find temperatures of up to ~

20 K in the outskirts and between the cores, and down to ~ 10 K in the

cores themselves. The cores themselves are almost isothermal, although

their average temperatures vary between 10 K and 18 K. We used the

extinction data to derive in addition a map of the dust emissivity

parametrized by kappa '=kappa 850/kappa V. The

average value of kappa ' agrees well with the canonical value of Mathis

(1990). We find that kappa ' increases by a factor of ~ 4 from ~

1.3*E-5 to ~ 5*E-5 when the dust temperature

decreases from ~ 20 K to ~ 12 K. A Monte Carlo simulation shows that

this change is significant with regard to the estimated calibration

uncertainties. This is consistent with models of dust evolution in

prestellar cores by Ossenkopf & Henning (1994) which predict that

grain coagulation and the formation of ices on grain surfaces in the

cold, dense cloud interiors lead to a significant increase of the 850 mu

m dust opacity. This interpretation is furthermore supported by the

previous detection of gas-phase depletion of CO in one of the IC 5146

cores (Kramer et al. 1999). Observations of dust fluxes at short

wavelengths are however needed to verify this result.

Department of Astrophysics
External organisation(s)
University of Cambridge, Universität zu Köln, Harvard-Smithsonian Center for Astrophysics
Astronomy & Astrophysics
Publication date
Peer reviewed
Portal url