## Abstract

We investigate the properties of dark matter substructure in the gravitational lens HE 0435-1223 (z_{l}=0.455) via its effects on the positions and flux ratios of the quadruply imaged background quasar (z_{s}= 1.689). We start with a smooth mass model, add individual, truncated isothermal clumps near the lensed images and use the Bayesian evidence to compare the quality of different models. Compared with smooth models, models with at least one clump near image A are strongly favoured. The mass of this clump within its Einstein radius is log_{10}(M^{A}_{Ein}) = 7.65^{+0.87}_{- 0.84} (in units of h^{-1}_{70}M_{⊙}). The Bayesian evidence provides weaker support for a second clump near image B, with log_{10}(M^{B}_{Ein}) = 6.55^{+1.01}_{- 1.51}. We also examine models with a full population of substructure, and find the mass fraction in substructure at the Einstein radius to be f_{sub}>rsim 0.00077, assuming the total clump masses follow a mass function dN/dM∝M^{-1.9} over the range M= 10^{7}-10^{10}M_{⊙}. Few-clump and population models produce similar Bayesian evidence values, so neither type of model is objectively favoured.

Original language | English (US) |
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Pages (from-to) | 936-951 |

Number of pages | 16 |

Journal | Monthly Notices of the Royal Astronomical Society |

Volume | 419 |

Issue number | 2 |

DOIs | |

State | Published - Jan 2012 |

## All Science Journal Classification (ASJC) codes

- Astronomy and Astrophysics
- Space and Planetary Science

## Keywords

- Dark matter
- Galaxies: haloes
- Gravitational lensing: strong
- Methods: statistical