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Published March 11, 1999 | Published + Submitted
Journal Article Open

A new radio double lens from CLASS: B1127+385


We present the discovery of a new gravitational lens system with two compact radio images separated by 0.701 ± 0.001 arcsec. The lens system was discovered in the Cosmic Lens All Sky Survey (CLASS) as a flat-spectrum radio source. Both radio components show structure in a Very Long Baseline Array (VLBA) 8.4-GHz radio image. No further extended structure is seen in Very Large Array (VLA), Multi-Element Radio Linked Interferometer Network (MERLIN) or VLBA images. Hubble Space Telescope (HST) WFPC2 images in F555W and F814W show two extended objects close to the radio components, which we identify as two lens galaxies. Their colours and mass-to-light ratios seem to favour two late-type spiral galaxies at relatively high redshifts (z_d ≥ 0.5). Faint emission is also detected at positions corresponding to the radio images. A two-lens mass model can explain the observed VLBA structure. The best-fitting model has a reduced χ^2 of 1.1. The relative positions of the VLBA subcomponents are reproduced within 0.08 mas, and the flux density ratios within 20 per cent. We also reproduce the position angle and separation of the two VLBA subcomponents in A and B within the observational errors, which we consider strong evidence for the validity of the lens model. Moreover, we find a surface density axis ratio of 0.74^(+0.10)_(0.12) for the primary lens (G1), consistent with the surface brightness axis ratio of 0.69 ± 0.15. Also, the surface density position angle of (4.9^(+28.2)_(-22.4)° of G1 compares well with the (−6±13) position angle of the surface brightness distribution. The errors indicate the 99 per cent confidence interval.

Additional Information

© 1999 RAS. Accepted 1998 October 19. Received 1998 October 16; in original form 1998 February 12. LVEK and AGdeB acknowledge support from an NWO program subsidy (grant number 781-76-101). This research was supported in part by the European Commission, TMR Programme, Research Network Contract ERBFMRXCT96-0034 'CERES'. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. MERLIN is a national UK facility operated by the University of Manchester on behalf of PPARC. This research used observations with the Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by Associated Universities for Research in Astronomy Inc. under NASA contract NAS5-26555. The Westerbork Synthesis Radio Telescope (WSRT) is operated by the Netherlands Foundation for Research in Astronomy (ASTRON) with the financial support from the Netherlands Organization for Scientific Research (NWO).

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August 19, 2023
October 20, 2023