期刊
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
卷 390, 期 4, 页码 1647-1654出版社
OXFORD UNIV PRESS
DOI: 10.1111/j.1365-2966.2008.13852.x
关键词
galaxies: clusters: general; galaxies: formation; cosmological parameters; cosmology: theory; dark matter
资金
- ICRR in Tokyo, Japan
- John Simon Guggenheim Memorial Foundation
- Israel Science Foundation [629/05, 1218/06]
The Einstein radius of a cluster provides a relatively model-independent measure of the mass density of a cluster within a projected radius of similar to 150 kpc, large enough to be relatively unaffected by gas physics. We show that the observed Einstein radii of four well-studied massive clusters, for which reliable virial masses are measured, lie well beyond the predicted distribution of Einstein radii in the standard Lambda cold dark matter (Lambda CDM) model. Based on large samples of numerically simulated cluster-sized objects with virial masses similar to 10(15) M-circle dot, the predicted Einstein radii are only 15-25 arcsec, a factor of 2 below the observed Einstein radii of these four clusters. This is because the predicted mass profile is too shallow to exceed the critical surface density for lensing at a sizable projected radius. After carefully accounting for measurement errors as well as the biases inherent in the selection of clusters and the projection of mass measured by lensing, we find that the theoretical predictions are excluded at a 4 sigma significance. Since most of the free parameters of the Lambda CDM model now rest on firm empirical ground, this discrepancy may point to an additional mechanism that promotes the collapse of clusters at an earlier time thereby enhancing their central mass density.
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