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

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

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 backgr...

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Main Authors: Rui Li, Nicola R. Napolitano, Giuseppe D’Ago, Vyacheslav N. Shalyapin, Kai Zhu, Xiaotong Guo, Ran Li, Léon V. E. Koopmans, Chiara Spiniello, Crescenzo Tortora, Francesco La Barbera, Haicheng Feng, Liang Gao, Zhiqi Huang, Koen Kuijken, Hui Li, Linghua Xie, Mario Radovich, Alexey Sergeyev
Format: Article
Language:English
Published: IOP Publishing 2025-01-01
Series:The Astrophysical Journal Letters
Subjects:
Dark matter
Gravitational lensing
Galaxy dynamics
Galaxy formation
Galaxy evolution
Online Access:https://doi.org/10.3847/2041-8213/ade680
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Summary: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 Ly α 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 ${\gamma }_{\mathrm{tot}}=2.1{4}_{-0.07}^{+0.06}$ , 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) × 10 ^11 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.
ISSN:2041-8205

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