The Rapid ASKAP Continnum Survey (RACS) has produced detailed images and catalogues of the radio sky, which have been widely used by astronomers worldwide. Ighina et al. present a multi-wavelength study of three new high-redshift (z∼5.6) quasi-stellar objects (QSOs) identified from dedicated spectroscopic observations. The three sources were selected as high-z candidates based on their radio and optical/near-infrared properties as reported in the Rapid ASKAP Continuum Survey (RACS), the Dark Energy Survey (DES), and the Panoramic Survey Telescope and Rapid  Response System (Pan-STARRS) survey. These are among the most radio-bright QSOs currently known at z > 5.5, relative to their optical luminosity. These discoveries allow one of the main unsolved questions in current astrophysics and cosmology to be addressed: how did  the most massive supermassive black holes (SMBHs) in the early Universe form and grow to around a billion solar masses in such a short time?

The three sources present a wide range of properties in terms of relative intensity and spectral shape, highlighting the importance of multi-wavelength observations in accurately characterising these high-z objects. In particular, one source shows clear blazar properties (strong radio and X-ray emission), making it one of the most distant currently known in this class. The multi-wavelength characterisation of radio QSOs at z > 5.5, such as these, is essential to constraining the evolution of relativistic jets and supermassive black holes hosted in this class of objects. The images show the optical/NIR discovery spectra around the observed Lyman-alpha emission line of the new sources.  The significant drop at wavelengths shorter than the 912 angstrom Lyα line confirms the high-redshift nature of all the three objects, as radiation at higher energies, or shorter wavelengths, is almost completely absorbed by neutral gas around star-forming regions of galaxies.  The dashed line in each panel shows the composite spectrum at the best-fit redshift of each source.