1999A&A...343L..70S

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 z=1.062 based on the identification of [O II] 3727Å and [Ne V] 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±0.2. The absolute luminosities of the source are then L_B=1.3x10¹²L_B☉ and νL_ν≃4x10¹⁰L_☉ in the mid-IR.