D13 Gravitational Lensing: Strong Lensing in Galaxy Clusters

Topic

The key element of this model is strong gravitational lensing, a phenomenon that occurs when a concentration of mass deflects light from a background object, producing arcs, Einstein rings, or multiple images of that same object.

Two space telescopes with sub-arcsecond angular resolution currently serve as the benchmark instruments for resolving these structures: one captured deep images—in both optical and infrared light—of several massive clusters to reveal their gravitational arcs, while the more recent of the two surpasses it in the infrared, unveiling magnified galaxies at even higher redshifts.

Based on the positions and shapes of these arcs, the lens's complete two-dimensional mass profile—including its dark matter content—is reconstructed using either parametric or non-parametric techniques.

The most remarkable aspect of this combination is that the universe itself provides an additional, free telescope: a massive cluster acts as a cosmic magnifying glass, enlarging galaxies that would otherwise be invisible—indeed, this is how the most distant galaxy known to date was discovered. Furthermore, mapping the magnification at every point across the lensed field creates an effective depth map of the observable universe, enabling the systematic selection of objects with the highest redshifts. Thus, from the strong gravitational lensing that opens this discussion to the depth map that concludes it—taking in sub-arcsecond resolution telescopes and mass profile reconstruction along the way—gravitational lenses allow a single massive cluster to function, at no cost, as the most powerful telescope nature has gifted to astronomy.

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