Letter to the Editor

The first detection of weak gravitational shear in infrared observations: Abell 1689

¹ Institut für Astrophysik und Extraterrestrische Forschung, Auf dem Hügel 71, 53121 Bonn, Germany
² Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Strasse 1, 85741 Garching, Germany
³ European Southern Observatory, Casilla 19, Santiago, Chile
⁴ Institut d'Astrophysique de Paris, 98 bis Boulevard Arago, 75014 Paris, France
⁵ Observatoire de Paris, DEMIRM, 61 avenue de l'Observatoire, 75014 Paris, France
⁶ Observatoire Midi-Pyrénées, 14 Av. E. Belin, 31400 Toulouse, France
⁷ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA

Corresponding author: L. J. King, lindsay@astro.uni-bonn.de

Received: 14 January 2002
Accepted: 13 February 2002

Abstract

We present the first detection of weak gravitational shear at infrared wavelengths, using observations of the lensing cluster Abell 1689, taken with the SofI camera on the ESO-NTT telescope. The imprint of cluster lenses on the shapes of the background galaxy population has previously been harnessed at optical wavelengths, and this gravitational shear signal enables cluster mass distributions to be probed, independent of whether the matter is luminous or dark. At near-infrared wavelengths, the spectrophotometric properties of galaxies facilitate a clean selection of background objects for use in the lensing analysis. A finite-field mass reconstruction and application of the aperture mass (M_ap) statistic are presented. The probability that the peak of the M _ap detection (), arises from a chance alignment of background sources is only ~. The velocity dispersion of the best-fit singular isothermal sphere model for the cluster is , and we find a K-band mass-to-light ratio of ~ inside a radius.