Diagnostics of Baryonic Cooling in Lensing Galaxies

TL;DR

This study investigates the dark matter halo concentration in early-type galaxies using lensing and photometry, revealing discrepancies with standard adiabatic contraction models and suggesting additional processes like mass loss.

Contribution

It extends the c-Mvir relation to lower masses and challenges existing adiabatic contraction models with new observational constraints.

Findings

c-Mvir relation consistent with X-ray data at lower masses

Standard adiabatic contraction models are strongly disfavored

Additional mechanisms like mass loss are needed during halo contraction

Abstract

Theoretical studies of structure formation find an inverse proportionality between the concentration of dark matter haloes and virial mass. This trend has been recently confirmed for virial masses Mvir > ~6e12 Msun by the observation of the X-ray emission from the hot halo gas. We present an alternative approach to this problem, exploring the concentration of dark matter haloes over galaxy scales on a sample of 18 early-type systems. Our c-Mvir relation is consistent with the X-ray analysis, extending towards lower virial masses, covering the range from ~4e11 Msun up to 5e12 Msun. A combination of the lensing analysis along with photometric data allows us to constrain the baryon fraction within a few effective radii, which is compared with prescriptions for adiabatic contraction (AC) of the dark matter haloes. We find that the standard methods for AC are strongly disfavored, requiring additional mechanisms -- such as mass loss during the contraction process -- to play a role during the phases following the collapse of the haloes.