To Be Lensed or Not to Be Lensed: On the Nature of the Alleged High- z Lensed Quasars J0109–5424 and P170+20

We present a detailed multiwavelength analysis of two gravitationally lensed z > 6 quasar candidates: J0109–5424 and P170+20. Using JWST/NIRSpec near-infrared (NIR) data from the Aether survey, we demonstrate that J0109–5424 is in fact a FeLoBAL quasar at z = 2.07, exhibiting strong iron broad absorption lines that mimic the Lyman break. From the Pa β emission line, we estimate a black hole mass of 3.9 × 10 8 M ⊙ and a bolometric luminosity of L bol = 7.7 × 10 45 erg s −1 for this quasar. Follow-up HST/ACS Wide Field Channel imaging of P170+20 with the F555W filter, probing emission below the Lyman limit of the quasar, reveals a compact source located 0 . ″ 09 ± 0 . ″ 04 from the quasar position. Point spread function modeling and subtraction yield no evidence for extended emission. This is inconsistent with a foreground galaxy acting as a lens. Furthermore, we obtain Gemini South/Flamingos-2 and LBT/LUCI NIR observations to complement the existing optical Gemini North/GMOS spectrum of P170+20. Our spectral analysis shows that the observed spectral shape of P170+20 is consistent with a composite quasar and M dwarf spectrum. However, this interpretation remains uncertain, as a chance alignment between an ultracool dwarf and a quasar within 0 . ″ 1 would be unlikely. Overall, our findings establish J0109–5424 as an intermediate redshift source and do not favor the lensed nature of P170+20, although this possibility cannot be conclusively ruled out, highlighting the challenges of selecting lensed quasars at high redshift.