Fig. 4: Doppler enhancement and tension with the expected number of quasars at z ≈ 7.
a, Doppler enhancement diagram for different bulk Lorentz factors (Γ) and radio spectral indices (α = 0.85 for 2021 and α = 0.21 for 2022). J0410−0139 is classified as radio loud with R4400 = 74 (148), but its jet may be intrinsically weak depending on relativistic Doppler enhancement. The dashed lines indicate a Doppler enhancement of 7.4 (14.8), which is critical for reclassifying the quasar as radio quiet in 2021 (2022). The shaded region represents viewing angles where J0410−0139 would be intrinsically weak for the respective Γ. For larger angles, the jet power would be substantial, thus maintaining its classification as radio loud. b, Expected number of 6.9 < z < 7.7 quasars brighter than M1450 = −25.5 over 3.3π of the sky (covered by NVSS and VLASS) as a function of the fraction of quasars with relativistic jets. The thick horizontal red line represents the expected number based on the z ≈ 7 quasar UV luminosity function, and the shaded region indicates the 1σ uncertainty41. The existence of this blazar suggests that there are ~2Γ2 quasars with similar properties but misaligned jets. The orange region shows the expected number of comparable quasars assuming typical low-redshift blazar values27 of Γ = 4–15 as a function of the jetted fraction (fjetted): Ntotal = Njetted/fjetted = 2Γ2/fjetted. The dashed line represents an average Γ = 5, consistent with observations29 at z > 4. This estimate is in tension with the UV luminosity function. The shaded blue region shows the measured radio-loud fraction40 at z = 6. If the jet from J0410−0139 is weak but appears radio loud due to beaming, the tension decreases if the jetted fraction of UV-bright quasar exceeds 70%. Conversely, if the jet from J0410−0139 is powerful and the radio-loud fraction remains 10% at z ≈ 7, the total number of quasars would exceed expectations by at least an order of magnitude. RL, radio loud; RQ, radio quiet.
