Three Millimeter Continuum Studies of Sagittarius B2

Details Three Millimeter Continuum Studies of Sagittarius B2 Three Millimeter Continuum Studies of Sagittarius B2

Mar 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996adil...yk...01k&link_type=abstract

NCSA Astronomy Digital Image Library

Astronomy and Astrophysics

Astronomy

Extinction, Galaxy: Center, Ism: Dust, Ism: H Ii Regions, Ism: Individual Name: Sagittarius B2, Radio Continuum: Ism, Stars: Formation

Scientific paper

Continuum emission at 78.5 and 106.9 GHz was observed in Sgr B2 with the Berkeley-Illinois-Maryland Array (BIMA) and combined with other continuum observations at 4.9, 8.3, 81.5, 84.9, 87.9, and 109.9 GHz. Spectral indicies near 3 mm are -0.31 +/- 0.03 and -0.2 +/- 0.2 for Sgr B2(N') and Sgr B2(W), respectively, and are attributed to the optically thin free-free emission. Free-free emission contributes significantly to the 3 mm continuum in Sgr B2(M), but the positive slope of the continuum spectrum (spectral index = 1.0 +/- 0.3) indicates the presence of dust grains. Sgr B2(N) is dominated by thermal dust emission with a steep spectral index of 4.6 +/- 0.5. The 3 mm continuum spectra yield the grain emissivity exponents of 1.7 +/- 1.3 and 3.7 +/- 0.7 for Sgr B2(M) and Sgr B2(N), respectively. The grain emissivity law derived for Sgr B2(N) is significantly higher than most for other molecular clouds. Thus, Sgr B2(N) appears to be a very unusual dust core. The most likely explanation is that the region contains ice coated core-mantle grains. The existence of ice coated core-mantle grains implies the mean dust temperature in the Sgr B2(N) dust core is < 150 K. The short life time of the core-mantle phase and the high value of n(H2) indicate that Sgr B2(N) is quite young and in a very early stage of star formation.

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