2017MNRAS.464L..46S

I report discovery of a new galaxy-scale gravitational lens system, identified using public data from the Mapping Galaxies at Apache Point Observatory (MaNGA) survey, as part of a systematic search for lensed background line emitters. The lens is SDSS J170124.01+372258.0, a giant elliptical galaxy with velocity dispersion σ = 256 km s^–1, at a redshift of z_l = 0.122. After modelling and subtracting the target galaxy light, the integral-field data cube reveals [O II], [O III] and Hβ emission lines corresponding to a source at z_s = 0.791, forming an identifiable ring around the galaxy centre. If the ring is formed by a single lensed source, then the Einstein radius is R_Ein ≃ 2.3 arcsec, projecting to ∼5 kpc at the distance of the lens. The total projected lensing mass is M_Ein = (3.6 ± 0.6) x 10¹¹ M_☉, and the total J-band mass-to-light ratio is 3.0 ± 0.7 solar units. Plausible estimates of the likely dark matter content could reconcile this with a Milky Way-like initial mass function (IMF), for which M/L ≃ 1.5 is expected, but heavier IMFs are by no means excluded with the present data. An alternative interpretation of the system, with a more complex source plane, is also discussed. The discovery of this system bodes well for future lens searches based on MaNGA and other integral-field spectroscopic surveys.