The giant molecular cloud Sagittarius B2 (hereafter SgrB2) is the most massive region with ongoing high-mass star formation in the Galaxy. Two ultra-compact HII (UCHII) regions were identified in SgrB2's central hot cores, SgrB2(M) and SgrB2(N). Our aim is to characterize the properties of the HII regions in the entire SgrB2 cloud. Comparing the HII regions and the dust cores, we aim to depict the evolutionary stages of different parts of SgrB2. We use the Very Large Array in its A, CnB, and D configurations, and in the frequency band C (~6GHz) to observe the whole SgrB2 complex. Using ancillary VLA data at 22.4GHz and ALMA data at 96GHz, we calculated the physical parameters of the UCHII regions and their dense gas environment. We identify 54 UCHII regions in the 6GHz image, 39 of which are also detected at 22.4GHz. Eight of the 54 UCHII regions are newly discovered. The UCHII regions have radii between 0.006pc and 0.04pc, and have emission measure between 10^6^pc/cm^6^ and 10^9^pc/cm^6^. The UCHII regions are ionized by stars of types from B0.5 to O6. We found a typical gas density of ~10^6^-10^9^cm^-3^ around the UCHII regions. The pressure of the UCHII regions and the dense gas surrounding them are comparable. The expansion timescale of these UCHII regions is determined to be ~10^4^-10^5^yr. The percentage of the dust cores that are associated with HII regions are 33%, 73%, 4%, and 1% for SgrB2(N), SgrB2(M), SgrB2(S), and SgrB2(DS), respectively. Two-thirds of the dust cores in SgrB2(DS) are associated with outflows. The electron densities of the UCHII regions we identified are in agreement with that of typical UCHII regions, while the radii are smaller than those of the typical UCHII regions. The dust cores in SgrB2(N) are more evolved than in SgrB2(DS) but younger than in SgrB2(M).

Cone search capability for table J/A+A/666/A31/tableb1 (Photometry of UCHII regions in 6, 22.4 and 96GHz)

Cone search capability for table J/A+A/666/A31/list (Infornation on fits image)