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

TL;DR

This study uses Subaru FOCAS IFU observations to analyze two strong-lensing elliptical galaxies at z=0.12, confirming their lensing configurations, refining mass estimates, and providing insights into their stellar populations and dark matter content.

Contribution

First detailed IFU spectroscopic analysis of these galaxies, revealing new lensing features and refining mass and IMF estimates compared to previous studies.

Findings

Confirmed cusp configuration with Einstein radius 2.0 arcsec for J1436+4943

Discovered inner counter-image, reducing Einstein radius to 1.6 arcsec for J1701+3722

Mass estimates suggest a Milky Way-like IMF with ~35% dark matter contribution

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.