Resolving the baryon-fraction profile in lensing galaxies

TL;DR

This study maps the radial distribution of stellar baryon fractions in 21 lensing galaxies, revealing how dark matter and stellar content vary with radius and mass, and providing insights into galaxy structure and formation.

Contribution

It presents the first detailed analysis of baryon fraction profiles across a wide mass range in lensing galaxies, linking these profiles to galaxy formation models and the Fundamental Plane.

Findings

Dark matter overtakes stellar mass between 1.5 and 2.5 Re.

Stellar baryon fraction declines steadily with galaxy mass.

Profiles help evaluate star formation and adiabatic contraction models.

Abstract

We show the radial dependence of stellar baryon fraction curves derived for 21 lensing galaxies from the CfA-Arizona Space Telescope LEns Survey by means of stellar population synthesis and pixel-based mass reconstruction. The sample covers a stellar mass range of Ms~2x10^9-3x10^11 Msol (solar masses) which corresponds to a total mass range of ML~7x10^9-3x10^12 Msol on scales from 0.25 to 5 Re (effective radii). By examining the Ms-to-ML dependence on radial distance to the center of each galaxy we find pairs of lenses on small to intermediate mass scales which approach at large radii the same values for their enclosed total mass but exhibit very different stellar masses and stellar baryon fractions. This behaviour subsides for the most massive lenses. All baryon fraction profiles show that the dark matter halo overtakes the stellar content between 1.5 and 2.5 Re. We find evidence for a stellar baryon fraction steadily declining over the full mass range. We shed light on the Fundamental Plane puzzle by showing that the slope of the ML(<R)-to-Ms(<R) relation approaches the mass-to-light relation of recent Fundamental Plane studies at large radii. Less massive dark matter halos turn out to be influenced by the distribution of stellar matter on resolved scales below 10 kpc. The ongoing study of resolved baryon fraction profiles will make it possible to evaluate the validity of star formation models as well as adiabatic contraction prescriptions commonly used in simulations. [abridged]