Gravitational flexion, its measurement and its application to galaxy clusters

点击翻译按钮获取中文摘要

Gravitational lensing by cosmic structures is one of the preferred methods for mapping the spatial distribution and the total amount of dark matter. For this purpose, the gravitational tidal field is routinely being used, the so-called gravitational shear, which can be measured from the elliptical distortions of the images of distant galaxies in the background of the gravitationally lensing objects. The angular resolution of such measurements is limited to angular scales of approximately half an arc minute. It would be desirable, however, to probe the distribution of dark matter also on smaller scales in order to test the hypothesis of cold dark matter.Access to such measurements is promised by the derivatives of the tidal field which can be combined to form quantities of single or three-fold rotational symmetry. They are called the F and G flexions, both of which have two components.The present application is meant to extend and conclude a previously granted project aiming at measuring for the first time both components of the flexions in a reliable and unbiased way. The work programme originally foreseen was delayed by considerable difficulties, which were uncovered and solved in the course of the work.We are now in a position to measure the flexions of realistically simulated galaxy images. During the further (fourth) year of the project, for which we apply for funding here, the measurement method developed so far will be extended to observational data and used for calibrating the statistical distribution of intrinsic flexions in galaxy images. Finally, the flexion will be used for the first time jointly with the shear to reconstruct the matter distribution of at least one galaxy cluster.