Follow-up observations have weakened the case for treating two unusual objects as high-redshift lensed quasars. J0109–5424, one of the alleged z > 6 candidates, was identified in JWST/NIRSpec data as a FeLoBAL quasar at z = 2.07. Its strong iron broad-absorption lines can mimic the apparent Lyman break. For P170+20, HST imaging found a compact source 0.09 ± 0.04 arcseconds from the target and no extended emission after point-spread-function modeling. The authors do not favor lensing for P170+20, but say it cannot be conclusively ruled out.
The analysis focused on two alleged z > 6 lensed-quasar candidates, J0109–5424 and P170+20. It used space- and ground-based multi-wavelength follow-up observations of both sources.
J0109–5424 changes category
For J0109–5424, the decisive change came from the spectrum. JWST/NIRSpec data identified it as a FeLoBAL quasar, meaning one with strong iron broad-absorption lines, at z = 2.07. Those lines can mimic the apparent Lyman break that formed part of the original high-redshift interpretation. The finding moves J0109–5424 out of that classification. It does not, however, show that the lower-redshift quasar cannot itself be lensed.
The revised classification also allowed estimates of the quasar's properties. A Paβ-based black-hole mass estimate came to 3.9 × 10^8 solar masses. Its Paβ-based bolometric luminosity was 7.7 × 10^45 erg per second, and its Eddington ratio was 0.16. Fitting the Paβ line gave a refined redshift of z = 2.0741 ± 0.0002. The absorption analysis estimated that He I absorption extended to at least -2,500 km/s, with another component offset by about 1,200 km/s, while noting that modeling limitations prevented a more detailed reading of the absorption.
P170+20 remains unsettled
P170+20 remains harder to classify. In HST/ACS WFC F555W imaging, the researchers found a compact source 0.09 ± 0.04 arcseconds from P170+20. After modeling the image's point-spread function, they found no extended emission. That weakens the case for an extended foreground galaxy acting as a lens, while leaving open a stellar explanation.
Spectral fitting gave the stellar explanation its clearest support. The best-fit model combined an M-dwarf spectrum with a quasar template redshifted to z = 6.39. The authors say this interpretation is uncertain and does not fully explain the break. They also tested an elliptical-galaxy model at z about 1.04. It could explain the break near 8,900 Å, but not the shape of the near-infrared spectrum. Together, the fits leave the identity of the foreground source unresolved.
One calculation shows why an alignment cannot be dismissed simply because it is rare. The estimated chance of one quasar–ultracool-dwarf alignment was about 0.01%. When the calculation was extended to more than 480 quasars, the estimate rose to about 4%. A single alignment would therefore be unusual, but the same kind of coincidence becomes plausible when a much larger group of quasars is considered. The calculation supports keeping the stellar interpretation in play, while not establishing that it is correct.
A clue that cuts both ways
The spectrum offers a second, conflicting clue. Foreground contamination meant that the proximity zone could not be measured reliably, although the cutoff in the GMOS spectrum could correspond to a zone no larger than about 1 Mpc. The authors say that possibility is compatible with an extremely young quasar or with a lensed quasar that is intrinsically fainter. Since the contamination prevents a reliable measurement, this clue cannot settle which explanation applies.
Taken together, the authors favor different conclusions for the two objects. J0109–5424 is interpreted as an intermediate-redshift FeLoBAL quasar, and its proposed high-redshift lensed-quasar identity is rejected. For P170+20, the preferred reading is a quasar seen along with an M-dwarf rather than a gravitational lens, although lensing remains possible. The competing explanations for P170+20 therefore remain unresolved.
The report is a preprint labeled arXiv:2608.25044v1 and dated 25 August 2026. Some of the analyzed observations are available through the Mikulski Archive for Space Telescopes, with an access DOI stated in the paper.
Paper data and sources
Original title: To be lensed or not to be lensed: on the nature of the alleged high-z lensed quasars J0109-5424 and P170+20
Authors: Aurora Mata-Sanchez, Emanuele P. Farina, Anniek J. Gloudemans et al.
Journal/Repository: arXiv
Status: Preprint, not yet peer-reviewed
First online: 2026-08-25
DOI: Not available
Original paper · Full text