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arXiv · 1511.01097

Light versus dark in strong-lens galaxies: Dark matter haloes that are rounder than their stars

Claudio Bruderer·Justin I. Read·Jonathan P. Coles·Dominik Leier·Emilio E. Falco·Ignacio Ferreras·Prasenjit Saha
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Abstract

We measure the projected density profile, shape and alignment of the stellar and dark matter mass distribution in 11 strong-lens galaxies. We find that the projected dark matter density profile - under the assumption of a Chabrier stellar initial mass function - shows significant variation from galaxy to galaxy. Those with an outermost image beyond $\sim 10$ kpc are very well fit by a projected NFW profile; those with images within 10 kpc appear to be more concentrated than NFW, as expected if their dark haloes contract due to baryonic cooling. We find that over several half-light radii, the dark matter haloes of these lenses are rounder than their stellar mass distributions. While the haloes are never more elliptical than $e_{dm} = 0.2$, their stars can extend to $e_* > 0.2$. Galaxies with high dark matter ellipticity and weak external shear show strong alignment between light and dark; those with strong shear ($γ\gtrsim 0.1$) can be highly misaligned. This is reassuring since isolated misaligned galaxies are expected to be unstable. Our results provide a new constraint on galaxy formation models. For a given cosmology, these must explain the origin of both very round dark matter haloes and misaligned strong-lens systems.

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Claudio Bruderer, Justin I. Read, Jonathan P. Coles, Dominik Leier, Emilio E. Falco, Ignacio Ferreras, Prasenjit Saha. 2015-11-03. Light versus dark in strong-lens galaxies: Dark matter haloes that are rounder than their stars. https://doi.org/10.1093/mnras%2Fstv2582

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