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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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