On the over-concentration problem of strong lensing clusters

Details On the over-concentration problem of strong lensing clusters On the over-concentration problem of strong lensing clusters

2010-01-11

arxiv.org/abs/1001.1696v1

Astronomy and Astrophysics

Astrophysics

Cosmology and Extragalactic Astrophysics

11 pages, 8 figures, in press on MNRAS

Scientific paper

Lambda cold dark matter paradigm predicts that galaxy clusters follow an universal mass density profile and fit a well defined mass-concentration relation, with lensing clusters being preferentially triaxial haloes elongated along the line of sight. Oddly, recent strong and weak lensing analyses of clusters with a large Einstein radius suggested those haloes to be highly over-concentrated. Here, we investigate what intrinsic shape and orientation an halo should have to account for both theoretical predictions and observations. We considered a sample of 10 strong lensing clusters. We first measured their elongation assuming a given mass-concentration relation. Then, for each cluster we found the intrinsic shape and orientation which are compatible with the inferred elongation and the measured projected ellipticity. We distinguished two groups. The first one (nearly one half) seems to be composed of outliers of the mass-concentration relation, which they would fit only if they were characterised by a filamentary structure extremely elongated along the line of sight, that is not plausible considering standard scenarios of structure formations. The second sample supports expectations of N-body simulations which prefer mildly triaxial lensing clusters with a strong orientation bias.

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