Astron. Astrophys. 320, 957-971 (1997)

6. Masses

From the sizes and densities obtained from , we have estimated the masses of the three molecular clouds, assuming that the size along the line of sight is equal to that in the plane of the sky. The results are summarized in Tables 3 and 4. The total mass for the hot cores plus the Sgr B2 Ridge ( pc), taking into account the three different clouds, is . The 55-66 cloud has the largest contribution () to the total mass. The previous total mass estimate does not include the mass of the lower density hot gas seen in absorption towards Sgr B2M. If we include the mass of the diffuse envelope with a mean density of (estimated in section 5.4) and a diameter of 27.5 pc, as proposed by Lis & Goldsmith (1989), the total estimated mass for Sgr B2 is in excellent agreement with previous estimates from data (Lis & Goldsmith, 1989) It is therefore very likely that a large fraction of the molecular gas surrounding the Sgr B2 ridge is hot and diffuse. This diffuse envelope would then contribute to more than half of the mass of the Sgr B2 molecular cloud. Our mass estimates for the dense envelope are, however, 5 times larger than those derived for the 1.3 mm dust emission by Gordon et al. (1993). This discrepancy is probably due to the extended dust emission, which is not recorded because beam switched observations were used to take the dust data. From our maps (see Fig. 4) the hydrogen density is still high () at distances larger than the full extent of the dust maps of Gordon et al. (1993).

Table 3. densities and masses for the components of the Sgr B2 Ridge.

Table 4. Sizes, densities and masses for the Sgr B2 hot cores. The sizes come from the kinetic temperature maps once deconvolved with a beam of . The assumed distance to Sgr B2 is 7.1 Kpc. The density was estimated from the analysis.

The sizes of the hot cores in Table 4 have been obtained by deconvolving the central hot regions with a beam. The sizes and masses for the cores Sgr B2M and Sgr B2N are larger than those obtained for the millimeter dust emission by Martín-Pintado et al. (1990) and Carlstrom & Vogel (1989) or from observations by Vogel at al. (1987). Our mass estimates are similar to those derived by Lis & Goldsmith (1990) from observations in the continuum. The difference between the masses from Vogel et al. (1987), Carlstrom & Vogel (1989) and Martín -Pintado et al. (1990) and ours is due to the different size and hydrogen density estimates for the hot cores. The emission also traces hot gas in both the very high density cores and from more diffuse molecular gas surrounding the cores.

© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998
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