A VLA/MERLIN/VLBA FOR INTERMEDIATE SCALE LENSES AND THE DISCOVERY OF A NEW LENS SYSTEM? P. AUGUSTO, P.N. WILKINSON AND I.W.A. BROWNE Nuffield Radio Astronomy Laboratories, Univ. of Manchester Jodrell Bank, Macclesfield, Cheshire, SK11 9DL, U.K. We are searching for small lens systems (50-250 mas or 10 8 —10 9 MQ) in a sample of ~ 1800 flat spectrum radio sources. This is the first time a sys- tematic search has been made "between" the VLA and VLBI resolutions. Finding any would indicate the existence of other than the "conventional" spiral/elliptical lenses (only ~ 0.01% chance - Turner et al. (1984)). For example, faint galaxies are numerous (~ 10 6 gal/deg 2 - Lilly (1993), Glaze- brook et al. 1995), compact (HST Medium Deep Survey (MDS) - Griffiths et al. 1994) and ideally placed for lensing (< > ~ 0.6 - MDS, Smail et al. (1994); cf. Turner et al. 1984). Early-type dwarf galaxies (dE,N and cE), if extant at intermediate-z as favored by MDS are also obvious lens candidates. If no lenses are found, a limit 400 times better than the current one (Surdej et al. 1993), , < 0.001, will be placed on the cosmological density of compact objects {e.g. black holes) for the above mass range. From the JVAS (Patnaik et al. 1992) and the Cosmic Lens All Sky Survey (CLASS) (Browne et al. this volume) - we selected a parent sample of ~ 1800 objects satisfying . 4 _ 5 < 0.50 (S u oc v~ a ), Sl \ al > 100 mJy and \b n \ > 10 . The 67 "candidates" were selected from the visibility plots (the sources >50 mas) and constitute an interesting population: two thirds of the candidates have a ~ 0.3 — 0.4 whereas the parent sample has < a > = 0.0; in addition, the candidate sample is clearly dominated by empty fields (40%) whereas the parent sample has 60% of QSOs. Our 67 candidates were mapped with MERLIN "snapshots" at 5 GHz (4 15 min.). About 20 sources look very interesting for subsequent VLBA follow-up; the great majority of the remaining appear to be "core-jets". One arcsecond scale source, 2114+022, looked promising enough for long track MERLIN observations (see Fig.l) and it is a good lens candidate despite its very strange configuration; there will be a multi-frequency VLBA follow-up. 399 C. S. Kochanek and J. N. Hewitt (eds), Astrophysical Applications of Gravitational Lensing, 399-400. 1996 IAU. Printed in the Netherlands. available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0074180900231884 Downloaded from https://www.cambridge.org/core. IP address: 54.162.69.248, on 24 May 2020 at 23:28:18, subject to the Cambridge Core terms of use,