Contradiction between strong lensing statistics and a feedback solution to the cusp/core problem

TL;DR

This paper examines the contradiction between dark matter halo profiles suggested by rotation curves and those inferred from gravitational lensing, highlighting a tension in baryonic effects on galaxy centers.

Contribution

It provides an analysis of recent rotation curve data and lensing observations, revealing a fundamental conflict in the effects of baryons on galaxy core profiles.

Findings

Lensing data favors cuspy profiles, conflicting with core profiles from rotation curves.

High baryon densities can reconcile lensing with core profiles only if they steepen the mass profile.

There is a contradiction in how baryons are expected to modify galaxy centers.

Abstract

Standard cosmology has many successes on large scales, but faces some fundamental difficulties on small, galactic scales. One such difficulty is the cusp/core problem. High resolution observations of the rotation curves for dark matter dominated low surface brightness (LSB) galaxies imply that galactic dark matter halos have a density profile with a flat central core, whereas N-body structure formation simulations predict a divergent (cuspy) density profile at the center. It has been proposed that this problem can be resolved by stellar feedback driving turbulent gas motion that erases the initial cusp. However, strong gravitational lensing prefers a cuspy density profile for galactic halos. In this paper, we use the most recent high resolution observations of the rotation curves of LSB galaxies to fit the core size as a function of halo mass, and compare the resultant lensing probability to the observational results for the well defined combined sample of the Cosmic Lens All-Sky Survey (CLASS) and Jodrell Bank/Very Large Array Astrometric Survey (JVAS). The lensing probabilities based on such density profiles are too low to match the observed lensing in CLASS/JVAS. High baryon densities in the galaxies that dominate the lensing statistics can reconcile this discrepancy, but only if they steepen the mass profile rather than making it more shallow. This places contradictory demands upon the effects of baryons on the central mass profiles of galaxies.