Optical+Near-IR Analysis of a Newly Confirmed Einstein Ring at z ∼ 1 from the Kilo-Degree Survey: Dark Matter Fraction, Total and Dark Matter Density Slope, and Initial Mass Function*
Year: 2025
Type: article
Abstract: We report the spectroscopic confirmation of a bright blue Einstein ring in the Kilo-Degree Survey (KiDS) footprint: the Einstein “blue eye.” Spectroscopic data from X-Shooter at the Very Large Telescope (VLT) show that the lens is a typical early-type galaxy (ETG) at z l = 0.9906, while the background source is a Lyα emitter at z s = 2.823. The reference lens modeling was performed on a high-resolution Y-band adaptive-optics image from HAWK-I at VLT. Assuming a singular isothermal ellipsoid total mass density profile, we inferred an Einstein radius R Ein = 10.47 ± 0.06 kpc. The average slope of the total mass density inside the Einstein radius, as determined by a joint analysis of lensing and isotropic Jeans equations, is γ tot = 2.1 4 − 0.07 + 0.06 , showing no systematic deviation from the slopes of lower-redshift galaxies. This can be the evidence of ETGs developing through dry mergers plus moderate dissipationless accretion. Stellar population analysis with eight-band (gri ZYJHK s ) photometries from KiDS and VIKING shows that the total stellar mass of the lens is M* = (3.95 ± 0.35) × 1011 M ⊙ (Salpeter initial mass function (IMF)), implying a dark matter fraction inside the effective radius of f DM = 0.307 ± 0.151. We finally explored the dark matter halo slope and found a strong degeneracy with the dynamic stellar mass. Dark matter adiabatic contraction is needed to explain the posterior distribution of the slope, unless an IMF heavier than Salpeter is assumed.
Institutions: Zhengzhou University, Sun Yat-sen University, University of Cambridge, Universidad de Cantabria, National Academy of Sciences of Ukraine, O.Ya. Usikov Institute for Radiophysics and Electronics, Tsinghua University, Anqing Normal University, Beijing Normal University, University of Chinese Academy of Sciences, University of Groningen, Astronomical Observatory of Capodimonte, University of Oxford, National Institute for Astrophysics, Chinese Academy of Sciences, Yunnan Observatories, Leiden University, Leiden Observatory, Osservatorio Astronomico di Padova, Centre National de la Recherche Scientifique, Université Côte d'Azur, Lagrange Laboratory, Institute of Radio Astronomy, Observatoire de la Côte d’Azur, V. N. Karazin Kharkiv National University
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $2,400
Awards: G170708805, Cambridge Astronomical Survey Unit (CASU) (2023-2026): Powering Next Generation Survey Analysis and Processing, G2891413898, G4309168922, G4753320163, G5073340295, G5146301614, G5579061841, Cambridge Astronomical Survey Unit (CASU): Filling the Astronomical Data Lake (2020-2024), G7938846334, G7966350388, G8980717377
OpenAlex ID: W4412047150