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Structure formation in N-body simulations

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A lucky start

This internship was my first one I did not have any clue of where I wanted to go and what I wanted to do. Fortunately, the Master's administration kept in files the whole destinations of the former students, plus the new opportunities sent by the labs that were ok to welcome students. I took the email of all the labs I was interested in and I sent them an email to see if they would welcome me from mid April till end of June. I sent more or less fifty emails and I only got four real answers : two in England, one in Denmark and one in Sweden.

I focused on those four ones and started to gather information to know what I would work on, how I could get somewhere to live and all the facilities. It turns out that a Swedish scientist was replying very quickly to my emails and it was really helpful. My choice was going to be this internship when I learned that she was French, and this made our discussions easier.

I finally decided to go to Sweden, in Göteborg to work with Cathy. I found a room in a student residence and this internship was amazing, not only because the work was very interesting but also because I hang out with such great  guys from all over Europe, especially Spanish guys.


The Onsala Space Observatory - OSO

My internship took place in the Onsala Space Observatory - OSO - . It stands in the south of Göteborg and it takes forty five minutes by car to go there. As it is a radioastronomy observatory, it was built in a wildlife park in which all radio communications are forbidden.

As I said, OSO is a radioastronomy observatory and it is made up of two antennas and several buildings. The two antennas are used to probe the Universe in radio wavelengths. The first antenna is a 25-meter diameter antenna and it allows to probe the Universe in the millimeter wavelengths The second one, which is protected by a radom and allows to probe the Universe in the sub-millimeter wavelength, is a 20-meter diameter antenna and is younger than the former one.

OSO location The Observatory

What is great with radioastronomy is that you can probe the Universe whenever you want : day, night, sunny or rainy day. This is possible 'cause the atmosphere is transparent for radio wavelengths. Therefore it allows scientists to share out their observations among the whole year, day and night.

The two antennas can be used in two different ways : you can use them separately, which is the way they are used most of the time. But sometimes they are used together with several other antennas among Europe. This big observatory is the VLBI for Very Large Base Interferometer.


Finally, there are two buildings for the people who work in the Observatory. One is for the researcher and scientists, the one is for the engineers in charge of the good working of the antennas. There are also little houses to put up scientists who come for observations.

The 25-meter antenna The 250-meter antenna The Building

My work

For my first internship, I worked on a very mysterious aspect of astronomy : the cosmological problem of the Dark Energy. Briefly, the Universe is made for 0.1% of "known" energy from the whole electromagnetic spectrum. 15% of the Universe is Dark Matter. Astronomers can not see it but its effects can easily be observed among the galaxies. And finally, the rest of the Universe is made of Dark Energy.

For both Dark Matter and Dark Energy, astronomers can not figure out what it is. But contrary to Dark matter Dark Energy and its effects are hardly or completely impossible to to observe. The impact of Dark Energy can only be seen in mathematical equations.

So my work was to recover the data from the Internet which had been released by the Virgo consortium. Once I got them, I had to extract them from the compressed file.

These data are the results of big simulations : a million particles, and each particle represent a galaxy. These simulations were done for different ages of the Universe : z = 10, 8, 5, 2, 1.5, 1, 0.8, 0.5, 0.3 and 0

To explain the evolution of the Universe, there are several models like the OCDM, LamdaCDM, TauCDM (Cold Dark Matter). These models differ from each other by the initial conditions and lead to a different Universe evolution like an open one, a close one, ...

My work was to confront the results from the Virgo consortium and what is indeed observed. Thus I was able to tell which model suits the most to explain the evolution of the Universe.