WEAK GRAVITATIONAL LENSING BY A SAMPLE OF X-RAY-LUMINOUS CLUSTERS OF GALAXIES. III. SERENDIPITOUS WEAK LENSING DETECTIONS OF DARK AND LUMINOUS MASS CONCENTRATIONS

摘要

In the course of a weak gravitational lensing survey of 39 clusters of galaxies, covering a total sky area of ～1 deg~2, we have serendipitously discovered mass concentrations in the fields of A1705 and A1722 that are most probably not associated with the main cluster target. By combining weak lensing information with two-color galaxy photometry in fields centered on our sample clusters, we identify a new cluster candidate at z ～ 0.5 in the field of A1705. This cluster candidate also displays strong lensing in the form of a giant luminous arc. The new mass concentration in the field of A1722 also seems to be associated with an optically luminous cluster of galaxies at z ～ 0.5, but in this case there is some evidence for additional structures along the line of sight that may contribute to the lensing signal. A third cluster, A959, has a dark subclump that shows interesting morphological evidence in the mass map for being associated with the main cluster. This is the first case where there is any significant evidence for a physical association between a dark subclump (discovered from weak lensing) and a normal cluster. Analysis of archival X-ray data shows that the three new mass concentrations are not firmly detected in X-rays and that they are X-ray―underluminous.