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13th of February 2023
New Radio-Loud QSOs at the end of the Re-ionisation Epoch
by Ighina et al.
Ighina et al. present the selection of high-redshift (z > 5.7) radio-loud (RL) quasi-stellar object (QSO) candidates from the combination of the radio Rapid ASKAP Continuum Survey (RACS) and the optical/near-infrared Dark Energy Survey (DES). Lyman-dropout galaxies were selected from the DES survey and counterparts searched for in the RACS catalogue. While several hundred z > 6 quasi-stellar objects are known, only about 10 of these are radio-loud. Having a large sample of RL AGNs at high-z will allow constraints to be placed on the cosmic evolution of super-massive black holes hosted in systems with powerful jets directly after their formation. The image above shows at left a 30 arsecond x 30 arcsecond cutout from a DES image of DES J0322−18 (bottom). The optical and radio positions are shown with an orange cross and a dashed red circle (uncertainty reported in the RACS catalogue), respectively, with VLASS (VLA Sky Survey) 3 GHz contours displayed in cyan. At right is the optical/near-infra-red spectra of DES J0318−18 (at z = 6.09) obtained with the GMOS instrument on the Gemini-South telescope. The dashed black lines are the smoothed spectra. The red and blue vertical lines indicate the expected wavelength of the Lyman-alpha emission line. The solid magenta line is a smoothed composite spectrum expected for sources like these.

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