Subaru FOCAS IFU observations of two z=0.12 strong-lensing elliptical galaxies from SDSS MaNGA

Abstract: We present new observations of two z=0.12 strong-lensing elliptical galaxies, originally discovered from the SDSS-IV MaNGA survey, using the new FOCAS IFU spectrograph on the Subaru Telescope. For J1436+4943, our observations confirm the identification of this system as a multiple-image lens, in a cusp configuration, with Einstein radius $\theta_{Ein}$=2.0 arcsec. For J1701+3722, the improved data confirm earlier hints of a complex source plane, with different configurations evident in different emission lines. The new observations reveal a previously unseen inner counter-image to the [OIII] arc found from MaNGA, leading to a smaller revised Einstein radius of $\theta_{Ein}$=1.6 arcsec. The inferred projected masses within the Einstein apertures (3.7-4.7kpc) are consistent with being dominated by stars with an initial mass function (IMF) similar to that of the Milky Way, and a dark matter contribution of ~35 per cent as supported from cosmological simulations. These results are consistent with `pure lensing' analyses of lower-redshift lenses, but contrast with claims for heavier IMFs from combined lensing-and-dynamical studies of more distant early-type galaxies.