The Rapid ASKAP Continnum Survey (RACS) has produced detailed images and catalogues of the radio sky, which have been widely used by the international astronomy community. 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 RACS data and optical/near-infrared properties. 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 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 above show optical/NIR images of the three sources. Images are from the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) survey in the case of PSO J0202−17 and PSO J1011−01 and from the Dark Energy Survey (DES) in the case of DES J0209−56.  The solid orange circle indicates the optical position, while the dashed red circle is the uncertainty of the radio position of each object reported the RACS-low source list (∼2 arcseconds).