2018 projects

A fundamental assumption in cosmology, known as the Cosmological Principle, is that the Universe is isotropic and homogeneous on large scales. The validity of this assumption can now be tested with current data, especially the massive spectroscopic surveys, which map the 3D map distribution of galaxies.

The SDSS/eBOSS/ELG (2016-2018) survey is the current largest spectroscopic survey at a redshift z~0.85, i.e. when the Universe was ~6.5 Gyrs old. This project proposes to test the assumption that the Universe is homogeneous at z~0.85 with the eBOSS/ELG data.

It will use the same methodology as Laurent et al. (2016, https://arxiv.org/abs/1602.09010) and Ntelis et al. (2017, https://arxiv.org/abs/1702.02159), which demonstrated with the SDSS data that the Universe was indeed homogeneous at higher and lower redshifts, respectively.


Baryon Acoustic Oscillations (BAOs) provide a cosmological standard ruler with which to measure the expansion history of the Universe and probe the nature of dark energy.

BAOs were produced in the early Universe by sound waves propagating in the primordial plasma, and have imprinted a characteristic scale in the clustering of matter. The result is an excess number of galaxies separated by a distance of about 150Mpc.

This work proposes to study a new way of investigating the BAO feature, by looking at a new scale in the correlation function of galaxies called the “linear-point” (https://arxiv.org/abs/1703.01275).

This “linear point” method is promising as it is insensitive to many assumptions made in the standard BAO scale measurement (non-linear gravity, redshift space distorsions and scale-dependent bias). It is also independent of the power spectrum of the primordial density fluctuations parameters. These properties make the “linear point” a very interesting and attractive tool for cosmology.



Strong lensing happens when the path of the light coming from a background galaxy or quasar is distorted by a foreground massive and compact object. The aim of this project is to search for strong lensing systems in the ~2 million galaxy and quasar spectra of the BOSS and eBOSS catalogs.

Spectra are provided with PCA templates of galaxy or quasar automatically fitted by the BOSS pipeline. Strong lensing candidates are identified by looking for emission lines in the spectra not associated with the template, indicating the presence of an additional galaxy along the line of sight of the object. The goal is to conduct a systematic search for such emission lines in both galaxy and quasar samples and will use machine learning to obtain an automated classification of the lens candidates.


Il s’agit d’analyser des images de galaxies autour d’amas à z~0.5 et de séparer les différentes  composantes stellaires: étoiles vieilles ou nouvellement formées. La méthode utilise les notions de sparsité des données astrophysique et décompose les distributions spectrales d’énergie des galaxies sur des bibliothèques choisies. Pour la première fois, la PSF des images sera prise en compte dans les calculs.

Les résultats serviront à comprendre l’influence des environnements denses sur l’évolution des galaxies et en particulier comment la formation s’éteint.

Référence: https://arxiv.org/abs/1603.00473

Simulations have largely increased in accuracy during this last decade through some better subgrid models and numerical methods but are not optimized enough to deal with high resolution and large volume.

The SWIFT code is emerging as the future of cosmological simulations due to its task based approach and deep optimization. While the code has been proved to be faster than its competitors, it still misses some physical comparison. Therefore this project consists in simulating an isolated disk (with a mass comparable to the Milky Way) and comparing to the most famous cosmological code (such as GADGET and RAMSES).

See https://arxiv.org/abs/1308.2669 for more information.