Cosmic Shear from STIS pure parallels^*

III. Analysis of Cycle 9 pure parallels

¹ Institut für Astrophysik und Extraterrestrische Forschung der Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany e-mail: miralles@astro.uni-bonn.de
² Max-Planck Institut für Astrophysik, Karl-Schwarzschild Str. 1, 85748 Garching bei München, Germany
³ ST-ECF, Karl-Schwarzschild Str. 2, 85748 Garching bei München, Germany

Received: 24 October 2003
Accepted: 10 November 2004

Abstract

Following the detection of a cosmic shear signal at the 30'' scale using archival parallel data from the STIS CCD camera onboard HST in the previous paper of this series, we analyzed a larger data set obtained from an HST GO pure parallel program. Although this data set is considerably larger than the one analyzed previously, we do not obtain a significant detection of the cosmic shear signal. The most likely cause of this null result is that the signal is comparable to (or less than) the random measurement of the noise. We also show that multiple systematics plague the STIS CCD data for its use in cosmic shear programs, and in particular the continuous degradation of the CCD charge transfer efficiency after 4 years in space, which is a source of additional noise that is still difficult to correct for in the absence of physical models.