Deconvolution of HST images of the Cloverleaf gravitational lens^*

Detection of the lensing galaxy and a partial Einstein ring

Institut d'Astrophysique et de Géophysique, Université de Liège, Allée du 6 Août 17, Sart Tilman (Bât. B5C), Liège 1, Belgium e-mail: Virginie.Chantry@ulg.ac.be

Received: 29 November 2006
Accepted: 28 March 2007

Abstract

Archival HST/NICMOS-2 images of the Cloverleaf gravitational lens (H1413+117), a quadruply-imaged quasar, were analysed with a new method derived from the MCS deconvolution algorithm (Magain et al. 1998). This method is based on an iterative process which simultaneously allows us to determine the Point Spread Function (PSF) and to perform a deconvolution of images containing several point sources plus extended structures. As such, it is well-adapted to the processing of gravitational lens images, especially in the case of multiply-imaged quasars. Two sets of data were analysed: the first one, which was obtained through the F160W filter in 1997, basically corresponds to a continuum image, while the second one, obtained through the narrower F180M filter in 2003, is centered around the forbidden [Oiii] emission lines at the source redshift, thus probing the narrow-line region of the quasar. The deconvolution gives astrometric and photometric measurements in both filters and reveals the primary lensing galaxy as well as a partial Einstein ring. The high accuracy of the results is particularly important in order to model the lensing system and to reconstruct the source undergoing the strong lensing. The reliability of the method is checked on a synthetic image similar to H1413+117.