Estimating distance, pressure, and dust opacity using submillimeter observations of self-gravitating filaments

We present a detailed study of the surface brightness profiles of dense filaments in IC 5146 using recent Herschel observations done with SPIRE. We describe the profile through an equilibrium solution of a self-gravitating isothermal cylinder pressure confined by its surrounding medium. In this first analysis we applied a simple modified black body function for the emissivity, neglecting any radiative transfer effects. Overall we found a good agreement of the observed surface brightness profiles with the model. The filaments indicate strong self-gravity with mass line densities M/l > similar to 0.5(M/l)(max) where (M/l)(max) is the maximum possible mass line density. In accordance with the model expectations we found a systematic decrease of the FWHM, a steepening of the density profile, and for filaments heated by the interstellar radiation field a decrease of the luminosity to mass ratio for higher central column density and mass line density. We illustrate and discuss the possibility of estimating the distance, external pressure, and dust opacity. For a cloud distance D similar to 500 pc and a gas temperature of T-cyl = 10 K the model implies an external pressure p(ext)/k similar to 2 x 10(4) K cm(-3) and an effective dust emission coefficient at 250 mu m given by delta kappa(em)(0) similar to 0.0588 cm(2) g(-1) where d is the dust-to-gas ratio. Given the largest estimate of the distance to the cloud complex, 1 kpc, the model yields an upper limit delta kappa(em)(0) similar to 0.12 cm(2) g(-1).