The total density profile of DM halos fitted from strong lensing

TL;DR

This study fits the total density profile of dark matter halos from strong lensing data using a double power-law model, revealing discrepancies with observed galaxy rotation curves and highlighting challenges in the $ ext{Lambda}$CDM paradigm.

Contribution

It introduces a new fit of the density profile based on strong lensing observations and compares it with rotation curve data, emphasizing existing tensions in $ ext{Lambda}$CDM models.

Findings

Fitted density profile parameters: α=3.04, β=1.39, γ=1.88.

Rotation curves from the fitted profile are lower than observed.

Highlights difficulty in reconciling lensing and rotation curve data in $ ext{Lambda}$CDM.

Abstract

In cosmological N-body simulations, the baryon effects on the cold dark matter (CDM) halos can be used to solve the small scale problems in $\Lambda$CDM cosmology, such as cusp-core problem and missing satellites problem. It turns out that the resultant total density profiles (baryons plus CDM), for halos with mass ranges from dwarf galaxies to galaxy clusters, can match the observations of the rotation curves better than NFW profile. In our previous work, however, we found that such density profiles fail to match the most recent strong gravitational lensing observations. In this paper, we do the converse: we fit the most recent strong lensing observations with the predicted lensing probabilities based on the so-called $(\alpha,\beta,\gamma)$ double power-law profile, and use the best-fit parameters ($\alpha=3.04, \beta=1.39, \gamma=1.88$) to calculate the rotation curves. We find that, at outer parts for a typical galaxy, the rotation curve calculated with our fitted density profile is much lower than observations and those based on simulations, including the NFW profile. This again verifies and strengthen the conclusions in our previous works: in $\Lambda$CDM paradigm, it is difficult to reconcile the contradictions between the observations for rotation curves and strong gravitational lensing.