Astronomy and Astrophysics – Astrophysics
Scientific paper
2006-08-09
Mon.Not.Roy.Astron.Soc.Lett. 372 (2006) L73-L77
Astronomy and Astrophysics
Astrophysics
6 pages, 4 figures, 1 table, accepted by MNRAS letters
Scientific paper
10.1111/j.1745-3933.2006.00230.x
We use high-resolution $N$-body simulations to investigate the optical depth of giant arcs with length-to-width ratio larger than 7.5 and 10 in the `standard' $\LCDM$ model with $\sigma_8=0.9$ and $\Omega_{\rm m,0}=0.3$ and a model based on three-year Wilkinson Microwave Anisotropy Probe (WMAP) data. We find that, in dark-matter only simulations, the lensing probability in the three-year WMAP model (with $\sigma_8=0.74$ and $\Omega_{\rm m,0}=0.238)$ decreases by a factor of $\sim 6$ compared with that in the `standard' $\LCDM$ model. The effects of baryonic cooling, star formation and feedbacks are uncertain, but we argue that baryons will only increase the the lensing cross-section by a moderate factor, $\sim 2$. We conclude that the low central value of $\sigma_8$ and $\Omega_{\rm m,0}$ preferred by the WMAP three-year data may be too low to be compatible with observations if conventional assumptions of the background source population are correct.
Gao Lan
Jing Yi-Peng
Li Guang-Liang
Lin Wei-Peng
Mao Shijun
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