2001A&A...367..741S

We present new optical data on the cluster AX J2019+1127 identified by the X-ray satellite ASCA at z∼1 (Hattori, 1997Natur.388..146H). The data suggest the presence of a high-redshift cluster of galaxies responsible for the large separation triple quasar MG 2016+112. Our deep photometry reveals an excess of z∼1 galaxy candidates, as already suspected by (Benitez, 1999ApJ...527...31B). Our spectroscopic survey of 44 objects in the field shows an excess of 6 red galaxies securely identified at z∼1, with a mean redshift of z =1.005±0.002. We estimate a velocity dispersion of σ=771⁺⁴³⁰_–160km/s based on these 6 galaxies and a V-band mass-to-light ratio of 215⁺³⁰⁸_–77h₅₀(M/L_V)_☉. Our observations thus confirm the existence of a massive structure acting as the lens, which explains the unusual configuration of the triple quasar. Hence, there is no need to invoke the existence of a ``dark cluster'' to understand this lens system.