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Astron. Astrophys. 343, L70-L74 (1999)

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Letter to the Editor

A ring galaxy at z = 1 lensed by the cluster Abell 370 *

G. Soucail 1, J.P. Kneib 1, J. Bézecourt 1,2, L. Metcalfe 3, B. Altieri 3 and J.F. LeBorgne 1

1 Observatoire Midi-Pyrénées, Laboratoire d'Astrophysique, UMR 5572, 14 Avenue E. Belin, F-31400 Toulouse, France
2 Kapteyn Institute, Postbus 800, 9700 AV, Groningen, The Netherlands
3 ISO Data Centre, Astrophysics Division, Space Science Department of ESA, Villafranca del Castillo, P.O. Box 50727, E-28080 Madrid, Spain

Received 12 January 1999 / Accepted 26 January 1999


We present a study of a very peculiar object found in the field of the cluster-lens Abell 370. This object displays, in HST imaging, a spectacular morphology comparable to nearby ring-galaxies. From spectroscopic observations at the CFHT, we measured a redshift of [FORMULA] based on the identification of [OII ] 3727Å and [NeV ] 3426Å emission lines. These emission lines are typical of starburst galaxies hosting a central active nucleus and are in good agreement with the assumption that this object is a ring galaxy. This object is also detected with ISO in the LW2 and LW3 filters, and the mid Infra-Red (MIR) flux ratio favors a Seyfert 1 type. The shape of the ring is gravitationally distorted by the cluster-lens, and in particular by a nearby cluster elliptical galaxy. Using our cluster mass model, we can compute its intrinsic shape. Requiring that the outer ring follows an ellipse we constrain the M/L ratio of the nearby galaxy and derive a magnification factor of 2.5 [FORMULA] 0.2. The absolute luminosities of the source are then [FORMULA] and [FORMULA] [FORMULA] [FORMULA] in the mid-IR.

Key words: galaxies: individual: LRG J0239 – 0134 – galaxies: evolution – galaxies: interactions – galaxies: Seyfert – cosmology: observations – cosmology: gravitational lensing

* Based on observations with the NASA/ESA Hubble Space Telescope obtained from the data archive at the Space Telescope European Coordinating Facility, with ISO; an ESA project with instruments funded by ESA Member States with the participation of ISAS and NASA, and with the Canada-France-Hawaii Telescope at Mauna Kea, Hawaii, USA.

Send offprint requests to: G. Soucail (soucail@obs-mip.fr)

© European Southern Observatory (ESO) 1999

Online publication: March 1, 1999