Different richness of compact radio sources in massive star forming regions

Recent results have shown different richness of compact radio sources in massive star-forming regions, but the reason for these differences are not clear yet. These compact radio sources are associated with young stellar objects that are related to different phenomena, such as jets, ionized disks, magnetically active stars, colission winds of binary massive stars or background quasars. Then, the characterization of these compact radio sources is crucial to understand the environments where high-mass stars form. Currently, we are studying the compact radio sources and their nature through deep continuum observations taken with the Very Large Array, an interferometer located in the USA, in a sample of massive star-forming regions. In this talk, I will show a catalog of compact sources in M17 region, their nature analysis and the comparison with the compact radio source populations previously studied to other star-forming regions like Orion and NGC 6334D-F. M17 is one of the most studied in HII regions, its cloud is even more massive than the Orion Nebula, and the number of detected sources is very large despite its distance. This is the first time that someone detects many radio sources in M17 region. I will also present the results for the counterpart in ALMA of the UC1 hypercompact HII region where there is a compact millimeter source that is probably related with the ionizing star. Finally, I will present preliminary results obtained for the environment of the NGC 6334A ultracompact HII region. This region has a square-shaped extended emission with a central compact source that is resolved with high-resolution for first time revealing an arc-shape morphology, suggesting a bow-shock nature produced by a binary system. Its spectral index shows thermal and non-thermal emission along the central source. In comparison with M17, NGC 6334A has far less compact sources. A possible explanation could be related with the much earlier evolutionary stage of NGC 6334A.