Dust and gas in the cores and the envelope in Sagittarius B2.

High-angular-resolution radio observations and thermal-emission measurements are reported for Sgr B2. Data obtained in the continuum at 4.8 GHz and in the J(KaKc) = 1(10)-1(11) absorption line of H2CO using the D configuration of the VLA (Martin-Pintado et al.(1985) are presented in tables, graphs, and contour maps and compared with 23-GHz continuum measurements obtained with the 100-m Effelsberg telescope and 3.2-mm, 1.3-mm, and H 41-alpha measurements obtained with the 30-m IRAM telescope. It is found that the absorption originates in a hot low-density envelope with dust optical depth greater than 1 at 50 microns. Two dust condensations are seen toward the most intense sources Sgr B2(M) and B2(N), coinciding with the NH3 maxima and having estimated masses 1800 and 2000 solar masses and LTE electron temperatures 9600 and 10,100 K, respectively.