To Be Lensed or Not to Be Lensed: On the Nature of the Alleged High- z Lensed Quasars J0109–5424 and P170+20
14 affiliations
- 1International Gemini Observatory/NSF NOIRLab
- 2INAF—Osservatorio di Astrofisica e Scienza dello Spazio di Bologna
- 3NSF NOIRLab
- 4University of California, Santa Cruz
- 5Max-Planck-Institut für Astronomie
- 6Institute for Fundamental Physics of the Universe
- 7INAF—Osservatorio Astronomico di Trieste
- 8University of Cambridge
- 9Center for Astrophysics ∣ Harvard & Smithsonian
- 10University of Hawai‘i
- 11University of Arizona
- 12Universidad Diego Portales
- 13University of Geneva
- 14University of Michigan
Abstract
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.
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BibTeX
@article{matasanchez2026lensed,
title = {{To Be Lensed or Not to Be Lensed: On the Nature of the Alleged High- z Lensed Quasars J0109–5424 and P170+20}},
author = {Aurora Mata-Sanchez and Emanuele Paolo Farina and Anniek J. Gloudemans and Debora Pelliccia and Roberto Decarli and Eduardo Bañados and Silvia Belladitta and Manuela Bischetti and Sarah E. I. Bosman and Xander Byrne and Thomas Connor and Frederick Davies and Thales A. Gutcke and Weizhe Liu and Chiara Mazzucchelli and Romain Meyer and Silvia Onorato and Fabian Walter and Feige Wang and Jinyi Yang},
journal = {The Astrophysical Journal},
year = {2026},
month = oct,
doi = {10.3847/1538-4357/ae9d7e},
url = {https://iopscience.iop.org/article/10.3847/1538-4357/ae9d7e},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - To Be Lensed or Not to Be Lensed: On the Nature of the Alleged High- z Lensed Quasars J0109–5424 and P170+20
AU - Aurora Mata-Sanchez
AU - Emanuele Paolo Farina
AU - Anniek J. Gloudemans
AU - Debora Pelliccia
AU - Roberto Decarli
AU - Eduardo Bañados
AU - Silvia Belladitta
AU - Manuela Bischetti
AU - Sarah E. I. Bosman
AU - Xander Byrne
AU - Thomas Connor
AU - Frederick Davies
AU - Thales A. Gutcke
AU - Weizhe Liu
AU - Chiara Mazzucchelli
AU - Romain Meyer
AU - Silvia Onorato
AU - Fabian Walter
AU - Feige Wang
AU - Jinyi Yang
PY - 2026
DA - 2026/10/01
JO - The Astrophysical Journal
DO - 10.3847/1538-4357/ae9d7e
UR - https://iopscience.iop.org/article/10.3847/1538-4357/ae9d7e
AB - 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.
SN - 0004-637X
SN - 1538-4357
ER -