Bremsstrahlung is also the dominant emission mechanism for H II regions at radio wavelengths.
In astronomy, collisional excitation gives rise to spectral lines in the spectra of astronomical objects such as planetary nebulae and H II regions.
Interstellar HO masers are often observed from molecular material surrounding ultracompact H II regions (UC H II).
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However, it is now classified as a transition object (T2), which is thought to be a LINER-type galaxy whose emission-line spectra is contaminated by H II regions in the nucleus.