All good things come in threes: The third image of the lensed quasar PKS 1830-211
Journal article, 2020

Strong gravitational lensing distorts our view of sources at cosmological distances but brings invaluable constraints on the mass content of foreground objects and on the geometry and properties of the Universe. We report the detection of a third continuum source toward the strongly lensed quasar PKS 1830-211 in ALMA multi-frequency observations of high dynamic range and high angular resolution. This third source is point-like and located slightly to the north of the diagonal joining the two main lensed images, A and B, 0.3″ away from image B. It has a flux density that is ∼140 times weaker than images A and B and a similar spectral index, compatible with synchrotron emission. We conclude that this source is most likely the expected highly de-magnified third lensed image of the quasar. In addition, we detect, for the first time at millimeter wavelengths, weak and asymmetrical extensions departing from images A and B that correspond to the brightest regions of the Einstein ring seen at centimeter wavelengths. Their spectral index is steeper than that of compact images A, B, and C, which suggests that they arise from a different component of the quasar. Using the GravLens code, we explore the implications of our findings on the lensing model and propose a simple model that accurately reproduces our ALMA data and previous VLA observations. With a more precise and accurate measurement of the time delay between images A and B, the system PKS 1830-211 could help to constrain the Hubble constant to a precision of a few percent.

Gravitational lensing: strong

Quasars: individual: PKS 1830-211


Sebastien Muller

Chalmers, Space, Earth and Environment, Onsala Space Observatory, Observation Support

Jaswanth Subramanyam

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics, Galactic Astrophysics

Cathy Horellou

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics, Extragalactic Astrophysics

Ivan Marti-Vidal

Universitat de Valencia

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 641 L2

Subject Categories

Astronomy, Astrophysics and Cosmology

Computer Vision and Robotics (Autonomous Systems)

Medical Image Processing



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