Sagittarius B2
Introduction
Sagittarius B2 (abbreviated as Sgr B2) is one of the most massive molecular clouds in the Galaxy. It is located at a distance of 8.34±0.16 kpc (Reid et al. 2014) and has a projected distance of 107 pc from Sgr A*, the compact radio source associated with the supermassive black hole located at the Galactic Center.
Hüttemeister et al. (1993) distinguish three different parts in Sgr B2:
At least three small clumps are sites of active star formation (Gordon et al. 1993). They are historically named according to their relative location in an equatorial coordinate system: Sgr B2(North), Sgr B2(Main) and SgrB2(South). These sources contain a plethora of (ultra-compact) Hii regions, X-ray sources, dense cores, embedded protostars, and molecular masers.
Hüttemeister et al. (1993) distinguish three different parts in Sgr B2:
- a low density envelope
- a moderate density region, that is extended around
- several small clumps, which are the most compact and densest molecular regions.
At least three small clumps are sites of active star formation (Gordon et al. 1993). They are historically named according to their relative location in an equatorial coordinate system: Sgr B2(North), Sgr B2(Main) and SgrB2(South). These sources contain a plethora of (ultra-compact) Hii regions, X-ray sources, dense cores, embedded protostars, and molecular masers.
Continuum radiative transfer modeling
Data: We model the thermal dust and free-free continuum emission using our Pandora framework. For this approach it is crucial to use multi-wavelength, multi-scale data to properly constrain the structure of Sgr B2. Towards the hot cores Sgr B2(N) and Sgr B2(M), the Herschel/HIFI spectral surveys (HEXOS project, PI: Ted Bergin) provide the continuum information from the sub-mm to the far-infrared regime. High-resolution interferometric maps towards both hot cores obtained with the Submillimeter Array (SMA) and the Very Large Array (VLA) provide the necessary spatial resolution on small scales. To cover the large-scale structure, we use dust continuum maps obtained within the APEX Telescope Large Area Survey of the Galaxy (ATLASGAL) and the Herschel infrared Galactic Plane Survey (HiGAL).
Large-scale modeling:
Small-scale modeling:
After managing to reconstruct the large-scale structure, we take a detailed look at the two hot cores Sgr B2(N) and Sgr B2(M). In this step we make use of the high resolution maps obtained with the VLA and the SMA. These maps allow to include the Hii regions (free-free emission) and the small-scale dust cores.
Sagittarius B2(N):
Sagittarius B2(N):
Sagittarius B2(M):
Stellar contribution: Stars provide the heating. In our models, they are assumed to be point sources.
- We account for observed early-type high-mass stars by including stars embedded in the known Hii regions (Mehringer et al. 1993; Gaume et al. 1995; De Pree et al. 1998).
- We account later spectral types are included (stars which produce Hii regions non-detectable with current observations). These stars are randomly drawn from Kroupas initial mass function (IMF).
Spectral energy distribution: In addition to the standard SED, where the continuum maps at each wavelength are convolved with the same beam (Figure to the left), it is now possible to convolve each continuum map with the telescope size, resulting in a wavelength-dependence of the beam size. This approach allows us to fit the SEDs obtained from the Herschel/HIFI observations (Figure to the right).
More analysis is included in our paper, which is published in A&A (ADS).