Universiteit Leiden

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Marie Curie grant for dark matter

Leiden Observatory is going to use a new technique to carry out calculations on gravitational lensing measurements. They will do this is the context of research into the formation of elliptical galaxies. Alessandro Sonnenfeld (University of Tokyo) who developed this technique joined the research team in Leiden. He recently obtained a Marie-Curie grant and will work with data from the KiloDegree survey.

Star formation

There are still many unanswered questions about the development of galaxies in the Milky Way. ‘These galaxies showed a phase of intense star formation around 10 bilion years ago,’ explains Sonnenfeld. ‘After this, a more quiescent phase followed, which continues to this day. It is not clear what physical mechanism caused those galaxies to stop forming stars.’

Dark matter

A still unexplored aspect of these galaxies may be the key to understanding their origins. It concerns the distribution of dark matter around the galaxies. This dark matter can be observed with weak gravitational lensing. A gravitational lens is a relatively strong gravitational field that deflects the lights from the objects behind it. The extent to which that happens, tells something about the mass distribution within the lens. By taking measurements on the deflecting light, scientists can thus determine the mass of the dark matter halos in which the galaxies are located.

New calculation method

However, it is quite difficult to map everything correctly, because the signal around individual galaxies is typically very low. This requires researchers to statistically combine measurements carried out over hundreds or thousands of objects. Sonnenfeld developed a new method for this, which is more accurate than the traditional methods. He explains that his approach is particularly useful for the exploration of correlations between halo mass and the visible matter of galaxies that occur in it. The aim is to gain more insight into the formation of galaxies.

During the Marie Curie fellowship, Sonnenfeld will apply his new technique to measurements from the KiloDegree Survey. Koen Kuijken, Professor of Galactic astronomy at Leiden University, set up this survey. The research group in Leiden plays an important role in the measurements, but also in their interpretation.

Golden age

The fellowship is actually a step towards an upcoming larger project. In 2022 ESA will launch a new satellite called Euclid. ‘With the launch of this satellite, we are about to enter a golden age for gravitational lens measurements,’ says Alessandro. ‘The quality and quantity of the data that this key mission will deliver will enable us to reach unprecedented precision in the measurement of dark matter halo masses.’ Henk Hoekstra, professor of Observational cosmology, will coordinate the project. 'The work that Alessandro is going to do with the KiloDegree Survey is a good preparation for this much larger and richer future data set.'

The Marie Skolodowska Curie actions (MSCA) are an initiative of the European Commission. The MSCA provides scholarships to make it more attractive for researchers to work in Europe. The scholarships are suitable for researchers who want to work abroad. Individual researchers, researchers at knowledge institutions or companies can apply for a scholarship. Organisations and companies that want to hire a researcher from abroad can also apply for a scholarship. An amount of € 5.6 billion has been made available for the period 2013-2020.

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