Continuum image of the Omega Nebula obtained with the SRT at 7.24 GHz. The source emission shown extends over about a 1^o × 1^o region. The RMS noise is ≃7 mJy/beam and the SRT resolution is 2.6 arcmin (SRT beam size at 7.24 GHz). The color map was biased to highlight the low surface brightness emission. As a result, the central and brightest part of the nebula (M17-UC1), characterized by a surface brightness in the range ≃3–100 Jy/beam, is saturated. Inset spectrum:6035 MHz OH maser emission (Jy) observed toward M17-UC1 is shown. Left and right circular polarizations are indicated in yellow and green, respectively. The spectrum was acquired with XARCOS, pointing at the position (J2000) RA = and Decl. = −16°11′37′′. The velocity scale refers to the local sidereal rest (LSR) frame and uses the optical convention. The velocity resolution is Δv = 10 m s^-1 and the RMS noise level is σ = 2 Jy/channel (for more details see Sect. 8).