### Abstract

We investigate the dependence of the ellipticities of clusters of galaxies on cosmological parameters using large-scale cosmological simulations. We determine cluster ellipticities out to redshift unity for λCDM models with different mean densities Ω_{m} and amplitudes of mass fluctuation σ_{8.0}. The mean ellipticity increases monotonically with redshift for all models. Larger values of σ_{8.0}, i.e., earlier cluster formation times, produce lower ellipticities. The dependence of ellipticity on Ω_{m} is relatively weak in the range 0.2 ≤ Ω_{m} ≤ 0.5 for high-mass clusters. The mean ellipticity ē(z) decreases linearly with the amplitude of mass fluctuations at the cluster redshift z, nearly independent of Ω_{m}; on average, older clusters are more relaxed and are thus less elliptical. The distribution of ellipticities about the mean is approximated by a Gaussian, allowing a simple characterization of the evolution of ellipticity with redshift as a function of cosmological parameters. At z = 0, the mean ellipticity of high-mass clusters is approximated by ē(z = 0) = 0.245 - 0.070σ_{8.0} + 0.020Ω_{m,0}. This relation opens up the possibility that, when compared with future observations of large cluster samples, the mean cluster ellipticity and its evolution could be used as a new, independent tool to constrain cosmological parameters, especially the amplitude of mass fluctuations, σ_{8.0}.

Original language | English (US) |
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Pages (from-to) | 8-12 |

Number of pages | 5 |

Journal | Astrophysical Journal |

Volume | 647 |

Issue number | 1 I |

DOIs | |

State | Published - Aug 10 2006 |

### All Science Journal Classification (ASJC) codes

- Astronomy and Astrophysics
- Space and Planetary Science

### Keywords

- Cosmology: theory
- Galaxies: clusters: general
- Large-scale structure of universe

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## Cite this

*Astrophysical Journal*,

*647*(1 I), 8-12. https://doi.org/10.1086/505255