le 05 Aug, 2017
As every year, the group Renoir welcomed students in their bachelor and master degree to perform their internship.
After an original research work, they were invited to describe their activities and are the subject of this news:
Marie Aubert
Cosmic voids occupy the majority of the universe and are part of large-scale structures. These structures are formed of filaments of galaxies and voids.
In order to determine the nature of dark energy, dominant in cosmic voids, we are interested in the way in which these structures were formed and grew through the rate of growth of structures. Its value is predicted in the context of General Relativity.
Using the catalogs of galaxies from the BOSS survey as well as the corresponding vacuum catalogs, I became interested in the cross-correlation between voids and galaxies, which makes it possible to evaluate material density fluctuations in the vicinity of the vacuum center as well as as the density profile of the vacuum. From these observational data, I was able to calculate the rate of growth of the structures, whose value is in agreement with the theory.
Joanna Berteaud
Among the different models of cosmology, the sneezing universe is a model that is based on the fact that there would be no beginning to the Universe. It would evolve through successive phases of contractions and dilations.
During my internship I tested the validity of this model of cosmology thanks to supernova observations and the study of the spectrum of acoustic oscillations of baryons. The results obtained showed an agreement between the cosmological model and the observations made. These same results even show that this model seems to correspond better than the classical model of the Big Bang, and that the observation of blue shift of the galaxy spectrum could bring a proof to this model.
Sylvain Gouyou Beauchamps
The matter of our universe is organized in a very particular way on a large scale, this is called the cosmic web. It is composed of very dense areas, filaments and clusters, and areas where the density of matter is lower, the cosmic voids. With the arrival of large boreholes like BOSS, recent studies have shown that the observation of voids allows us to measure the effects of dark energy, which is responsible for accelerating expansion. To observe these structures we must observe the galaxies that form them, it is they who trace the matter that we observe. It therefore seems important to know the influence that different tracers have on the definition of voids. The purpose of my internship at the CPPM was, from eBOSS data, to compare voids from two tracers, bright red galaxies and quasars, to quantify the influence of tracers on measurements.
Maxime Jabarian
The cosmological principle is based on the assumption that the universe is isotropic and uniform (the same in all directions of observations). In order to validate the use of cosmic voids for cosmology, my internship consisted in testing this cosmological principle on cosmic voids already observed.
For this, I used the data obtained by SDSS which mapped the location of a thousand galaxies and therefore thousands of cosmic voids. The results of the analysis showed that the isotropic hypothesis of the cosmological principle is well validated, which opens the way to demonstrate the principle of uniformity with the cosmic voids.
Modified 07 Feb, 2018