The physical and chemical structure of Sagittarius B2
I. Three-dimensional thermal dust and free-free continuum modeling on 100 au to 45 pc scales
1 I. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, 50937 Köln, Germany
2 Department of Astronomy, The University of Michigan, 500 Church Street, Ann Arbor, MI 48109-1042, USA
3 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
4 LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, 75014 Paris, France
5 California Institute of Technology, Pasadena, CA 91125, USA
6 INAF−Istituto di Astrofisica e Planetologia Spaziali, via Fosso del Cavaliere 100, 00133 Roma, Italy
7 Department of Astronomy, Yunnan University, and Key Laboratory of Astroparticle Physics of Yunnan Province, 650091 Kunming, PR China
Received: 4 September 2015
Accepted: 16 February 2016
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 = 40 GHz−4 THz). The model covers spatial scales from 45 pc down to 100 au, 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 8.0 × 106 M⊙ within a diameter of 45 pc. This corresponds to an averaged gas density of 170 M⊙ pc-3. We estimate stellar masses of 2400 M⊙ and 20 700 M⊙ and luminosities of 1.8 × 106 L⊙ and 1.2 × 107 L⊙ for Sgr B2(N) and Sgr B2(M), respectively. We report H2 column densities of 2.9 × 1024 cm-2 for Sgr B2(N) and 2.5 × 1024 cm-2 for Sgr B2(M) in a 40′′ beam. For Sgr B2(S), we derive a stellar mass of 1100 M⊙, a luminosity of 6.6 × 105 L⊙, and an H2 column density of 2.2 × 1024 cm-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.
Key words: radiative transfer / radio continuum: general / stars: formation / stars: massive / ISM: individual objects: Sgr B2 / ISM: clouds
© ESO, 2016