CALICE

Cosmological Applications of Lensing and Intrinsic Correlations of Ellipticities

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 Obiettivo del progetto (Objective)

'Cosmology has recently entered a concordance and precision era with its predictions being accurately and successfully tested by a number of observational probes. This status however is achieved at the expense of 96% of the Universe being assumed to be in still unknown forms known as Dark Matter and Dark Energy.

CALICE addresses open questions of Cosmology using Gravitational Lensing. This technique describes how light is deflected as it passes through the gravitational field generated by matter. Its effect can be detected in the distorted images of galaxies via a modification of their shapes. This “cosmic shear” effect is a unique probe of the geometry and matter distribution in the Universe. It has however its systematic effects which must be controlled to be efficiently used in future high precision surveys, such as the satellite Euclid mission.

Given the current and potential possibilities of cosmic shear, CALICE is divided in two parts. On one hand it will use data from CFHTLS and COSMOS surveys in three key goals. The first is to look for possible deviations of gravity effects from the ones predicted by General Relativity and study their evolution using tomographic measurements. The second is to study Dark Energy by combining lensing with measurements of the variation of the fine-structure constant and the proton-to-electron mass ratio. The third goal is to use the information on the evolution of matter distribution and its properties at large scales, to constrain the neutrinos mass.

On the other hand CALICE will contribute to the preparation of future surveys by conducting a study, using numerical simulations, of astrophysical effects that produce correlations in galaxies shapes, which contaminate the measurements. CALICE will produce detail modelling of various correlations as function of galaxy type, satellite distribution, magnitude and distance, creating a template to be used as a reference for removing such contaminations from future data.'

Introduzione (Teaser)

Invisible matter coming to light

Descrizione progetto (Article)

Long ago, Einstein recognised the potential existence of gravitational lensing, a consequence of his theory of general relativity. According to the theory, matter interacts gravitationally with any nearby objects, even with light. Consequently, dark matter lying between a telescope and a distant light source bends the light from the source as it travels toward the observer.

Scientists on the EU-funded project 'Cosmological applications of lensing and intrinsic correlations of ellipticities' (CALICE) focused on studying gravitational lensing in their quest to determine the Universe's make-up. Observing the coherent distortions on a large number of background galaxies at various distances reveals the dark matter distribution at different stages of the Universe's expansion. This tomographic weak lensing thus contains information about the expansion properties and consequently on dark energy and possible gravity effect deviations from Einstein's theory.

The methodology adopted in CALICE was based on developing a parameter estimation pipeline, made of a set of programming codes. This pipeline is able to predict the corresponding gravitational lensing signal from the dark energy model it includes. It can also be fed with observed or simulated data. Theoretical modelling and data analysis are merged in a statistical process to evaluate the likelihood of the theoretical models.

Based on this methodology, project members studied the viability of modified gravity models by modifying parameters in the general relativity equations. However, the observed gravitational lensing signal could be well explained with the standard gravitational theory. Furthermore, to provide an explanation for the increasing rate of the Universe's expansion, CALICE considered dark energy models containing late-time oscillations.

The project also attempted to study weak lensing effects on the cosmic microwave background radiation; it succeeded in producing its own measurements.

Project data will contribute to the large collaborative effort expended in the European Space Agency (ESA) Euclid Mission. This will map the gravitational lensing signal with high resolution and determine the need for dark matter or modifications in the theory of general relativity.