Gauging the dark matter fraction in a $L_*$ S0 galaxy at z=0.47 through gravitational lensing from deep HST/ACS imaging

TL;DR

This study uses gravitational lensing from deep HST imaging to measure the dark matter fraction in a specific galaxy at z=0.47, revealing it to be in transition between dark matter dominated and deficient systems.

Contribution

It provides the first lensing-based measurement of dark matter fraction in a L_* S0 galaxy at intermediate redshift, highlighting its transitional nature.

Findings

Dark matter fraction within Einstein radius is approximately 30%.

The galaxy's properties suggest it is in transition between different galaxy types.

The lensing galaxy's velocity dispersion is around 180 km/s.

Abstract

We analyze a new gravitational lens, OAC-GL J1223-1239, serendipitously found in a deep I-band image of the Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS). The lens is a L_*, edge-on S0 galaxy at z=0.4656. The gravitational arc has a radius of 0.42 arcsec. We have determined the total mass and the dark matter (DM) fraction within the Einstein radius as a function of the lensed source redshift, which is presently unknown. For z ~ 1.3, which is in the middle of the redshift range plausible for the source according to some external constraints, we find the central velocity dispersion to be ~180 km/s. With this value, close to that obtained by means of the Faber-Jackson relation at the lens redshift, we compute a 30% DM fraction within the Einstein radius (given the uncertainty in the source redshift, the allowed range for the DM fraction is 25-35 % in our lensing model). When compared with the galaxies in the local Universe, the lensing galaxy, OAC-GL J1223-1239 seems to fall in the transition regime between massive DM dominated galaxies and lower-mass, DM deficient systems.