A VLA/MERLIN/VLBA for Intermediate Scale Lenses and the Discovery of a New Lens System?

Abstract

We are searching for small lens systems (50-250 mas or 10⁸ – 10⁹ M _⊙) in a sample of ∼ 1800 flat spectrum radio sources. This is the first time a systematic 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 (∼ 10⁶ gal/deg² - Lilly (1993), Glazebrook et al. 1995), compact (HST Medium Deep Survey (MDS) - Griffiths et al. 1994) and ideally placed for lensing (< Z >∼ 0.6 - MDS, Smail et al. (1994); c.f. 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), Ω _L < 0.001, will be placed on the cosmological density of compact objects (e.g. black holes) for the above mass range.