2016A&A...588A.143S

Context. We model the dust and free-free continuum emission in the high-mass star-forming region Sagittarius B2.
Aims. We want to reconstruct the 3D density and dust temperature distribution, as a crucial input to follow-up studies of the gas velocity field and molecular abundances.
Methods. We employ the 3D radiative transfer program RADMC-3D to calculate the dust temperature self-consistently, providing a given initial density distribution. This density distribution of the entire cloud complex is then recursively reconstructed, based on available continuum maps, including both single-dish and high-resolution interferometric maps that cover a wide frequency range (ν=40GHz-4THz). The model covers spatial scales from 45pc down to 100au, i.e., a spatial dynamic range of 10⁵.
Results. We find that the density distribution of Sagittarius B2 can be reasonably well fitted by applying a superposition of spherical cores with Plummer-like density profiles. To reproduce the spectral energy distribution, we position Sgr B2(N) along the line of sight behind the plane containing Sgr B2(M). We find that the entire cloud complex comprises a total gas mass of 8.0x10⁶M☉ within a diameter of 45pc. This corresponds to an averaged gas density of 170M☉/pc³. We estimate stellar masses of 2400M☉ and 20700M☉ and luminosities of 1.8x10⁶L☉ and 1.2x10⁷L☉ for Sgr B2(N) and Sgr B2(M), respectively. We report H2 column densities of 2.9x10²⁴cm^–2 for Sgr B2(N) and 2.5x10²⁴cm^–2 for Sgr B2(M) in a 40'' beam. For Sgr B2(S), we derive a stellar mass of 1100M☉, a luminosity of 6.6x10⁵L☉, and an H₂ column density of 2.2x10²⁴cm^–2 in a 40'' beam. We calculate a star formation efficiency of 5% for Sgr B2(N) and 50% for Sgr B2(M). This indicates that most of the gas content in Sgr B2(M) has already been converted to stars or dispersed.