No Redshift Evolution in the Fe ii/Mg ii Flux Ratios of Quasars across Cosmic Time
Abstract The Fe ii /Mg ii emission line flux ratio in quasar spectra serves as a proxy for the relative Fe to α -element abundances in the broad-line regions of quasars. Due to the expected different enrichment timescales of the two elements, they can be used as a cosmic clock in the early Universe. We present a study of the Fe ii /Mg ii ratios in a sample of luminous quasars exploiting high-quality near-IR spectra taken primarily by the XQR-30 program with VLT XSHOOTER. These quasars have a median bolometric luminosity of log( L bol [erg s −1 ]) ∼ 47.3 and cover a redshift range of z = 6.0–6.6. The median value of the measured Fe ii /Mg ii ratios is ∼7.9 with a normalized median absolute deviation of ∼2.2. In order to trace the cosmic evolution of Fe ii /Mg ii in an unbiased manner, we select two comparison samples of quasars with similar luminosities and high-quality spectra from the literature, one at intermediate redshifts ( z = 3.5–4.8) and the other at low redshifts ( z = 1.0–2.0). We perform the same spectral analysis for all these quasars, including the usage of the same iron template, the same spectral fitting method, and the same wavelength fitting windows. We find no significant redshift evolution in the Fe ii /Mg ii ratio over the wide redshift range from z = 1 to 6.6. The result is consistent with previous studies and supports the scenario of a rapid iron enrichment in the vicinity of accreting supermassive black holes at high redshift.
Authors
- Linhua Jiang (ORCID: https://orcid.org/0000-0003-4176-6486)
- Masafusa Onoue (ORCID: https://orcid.org/0000-0003-2984-6803)
- Fabian Walter (ORCID: https://orcid.org/0000-0003-4793-7880)
- Jan–Torge Schindler (ORCID: https://orcid.org/0000-0002-4544-8242)
- M. Bischetti (ORCID: https://orcid.org/0000-0002-4314-021X)
- Martin G. Haehnelt (ORCID: https://orcid.org/0000-0001-8443-2393)
- Chiara Mazzucchelli (ORCID: https://orcid.org/0000-0002-5941-5214)
- Yongda Zhu (ORCID: https://orcid.org/0000-0003-3307-7525)
- Eduardo Bañados (ORCID: https://orcid.org/0000-0002-2931-7824)
- Samuel Lai (ORCID: https://orcid.org/0000-0001-9372-4611)
- Sarah E. I. Bosman (ORCID: https://orcid.org/0000-0001-8582-7012)
- R. L. Davies (ORCID: https://orcid.org/0000-0002-3324-4824)
- Emanuele Paolo Farina (ORCID: https://orcid.org/0000-0002-6822-2254)
- V. D’Odorico (ORCID: https://orcid.org/0000-0003-3693-3091)
- George D. Becker (ORCID: https://orcid.org/0000-0003-2344-263X)
- Danyang Jiang (ORCID: https://orcid.org/0009-0003-6747-2221)
Institutions
- University of California, Riverside (US)
- Australian National University (AU)
- Scuola Normale Superiore (IT)
- Universität Hamburg (DE)
- Kavli Institute for the Physics and Mathematics of the Universe (JP)
- Peking University (CN)
- Heidelberg University (DE)
- University of Cambridge (GB)
- Trieste Astronomical Observatory (IT)
- ASTRO-3D (AU)
- Gemini North Observatory (US)
- Kavli Institute for Theoretical Sciences (CN)
- Max Planck Institute for Astronomy (DE)
- Institute for Fundamental Physics of the Universe (IT)
- ARC Centre of Excellence for All-sky Astrophysics (AU)
- Swinburne University of Technology (AU)
- Heidelberg Institute for Theoretical Studies (DE)
- The University of Tokyo (JP)
- Universidad Diego Portales (CL)
Publication Details
- Journal
- The Astrophysical Journal
- Published
- 2024-11-01
- DOI
- https://doi.org/10.3847/1538-4357/ad7d09
- Citations
- 6
- Primary Topic
- Galaxies: Formation, Evolution, Phenomena
- Type
- article
- Field-Weighted Citation Impact
- 1.99
Funders
- National Science Foundation
- U.S. Department of Energy
- Alfred P. Sloan Foundation
- University of Utah
- National Radio Astronomy Observatory
- National Natural Science Foundation of China
- European Southern Observatory
- Office of Science