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 an Einstein radius θEin = 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 [O III] arc found from MaNGA, leading to a smaller revised Einstein radius of θEin = 1.6 arcsec. The inferred projected masses within the Einstein apertures (3.7–4.7 kpc) 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.