S19A0049abst
S19A0049
Low-redshift strong lenses yield uniquely-robust measurements of the stellar masses of galaxies, and hence offer a sensitive probe of possible variation in the stellar IMF as a function of galaxy properties. We have developed a novel method to discover such lenses, using IFUs to search for multiply-imaged line emission behind massive low-z elliptical galaxies. We have successfully applied this technique to data from SINFONI and MUSE at the VLT, discovering 4 systems so far, which are the only z<0.1 strong-lensing ellipticals known to date. All yield stellar mass measurements which are compatible with a Milky-Way-like IMF, and exclude the very heavy IMFs suggested for similarly massive galaxies from spectroscopic analysis (e.g. Conroy & van Dokkum 2012). However, with the current very small sample, we cannot exclude modestly heavy IMFs, nor assess galaxy-to-galaxy variations or correlations: more nearby lenses are urgently required. In S19A, we request observations with the new FOCAS IFU, to begin a similar search for low-redshift lenses, mainly in the northern sky. With the high sensitivity of FOCAS in the far red, we expect to discover 2β3 new lenses (a significant enlargement over our current sample), and substantially tighten the limits on IMF variation in massive ellipticals.
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