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Issue A&A
Volume 367, Number 3, March I 2001
Page(s) 741 - 747
Section Cosmology
DOI http://dx.doi.org/10.1051/0004-6361:20000498



A&A 367, 741-747 (2001)
DOI: 10.1051/0004-6361:20000498

Spectroscopic confirmation of a cluster of galaxies at $\vec{z=1}$ in the field of the gravitational lens MG 2016+112

G. Soucail1, J.-P. Kneib1, A. O. Jaunsen2, 3, J. Hjorth3, 4, 5, M. Hattori6 and T. Yamada6

1  Observatoire Midi-Pyrénées, Laboratoire d'Astrophysique, UMR 5572, 14 avenue E. Belin, 31400 Toulouse, France
2  Institute of Theoretical Astrophysics, University of Oslo, Pb. 1029, Blindern, 0315 Oslo, Norway
3  Centre for Advanced Study, Drammensvn. 78, 0271 Oslo, Norway
4  Astronomical Observatory, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark
5  NORDITA, Blegdamsvej 17, 2100 Copenhagen Ø, Denmark
6  Astronomical Institute, Tôhoku University, Aoba Aramaki, Sendai 980-77, Japan

(Received 11 July 2000 / Accepted 12 December 2000 )

Abstract
We present new optical data on the cluster AX J2019+1127 identified by the X-ray satellite ASCA at $z\sim 1$ (Hattori et al. 1997). 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 $z\sim 1$ galaxy candidates, as already suspected by Benítez et al. 1999. Our spectroscopic survey of 44 objects in the field shows an excess of 6 red galaxies securely identified at $z\sim 1$, with a mean redshift of $z =1.005\pm 0.002$. We estimate a velocity dispersion of $\sigma = 771^{+430}_{-160}$ km s-1 based on these 6 galaxies and a V-band mass-to-light ratio of $215^{+308}_{-77} h_{50} (M/L_V)_\odot$. 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.


Key words: cosmology: observations -- dark matter -- galaxies: clusters: general -- galaxies: clusters: individual: MG 2016+112 -- gravitational lensing -- X-rays: galaxies

Offprint request: G. Soucail, soucail@ast.obs-mip.fr

SIMBAD Objects in preparation



© ESO 2001


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