Study and calibration of the EUCLID/NISP Photo-Z for precision cosmology

Stage numéro : M2-2021-RE-02
Laboratoire :Centre de Physique des Particules de Marseille Case 902
 163 avenue de Luminy - 13288 Marseille Cedex 9
Directeur :Cristinel Diaconu - -
Correspondant :William Gillard - -
Groupe d'accueil :Renoir
Chef de groupe :Dominique Fouchez - -
Responsable de stage :William GILLARD - & Stephanie ESCOFFIER -

Thématique : Cosmologie observationnelle

The standard model of cosmology, known as the LCDM model, when confronted with observation, describes our Universe as being composed of 27% dark matter and 68% dark energy. Understanding the nature of these two energy components remains one of the greatest challenges of contemporary physics.

ESA's Euclid space mission, scheduled for launch in mid-2022, will constrain the evolutionary history of the Universe [H(z)] and the growth factor of large structures [f(z)], necessary to test Einstein's general relativity on large scales. Two instruments will be on board the Euclid satellite, the near-infrared spectro-photometer (NISP) and the visible imager (VIS), to map the Universe over a period of 6 years.

The NISP instrument, which combines an imager and a near-infrared spectrometer, is dedicated to the three-dimensional mapping of our Universe. The spectroscopic survey will observe 50 million galaxies in redshifts ranging from 0.9 to 1.8. The photometric survey will provide the image and the photometric redshift of two billion galaxies up to a magnitude of 24.5 AB covering the redshift range 0 < z < 2.5. The photometric sample, rich of its billions of galaxies, will be able to probe the Acoustic Baryonic Ocsillation (ABO) by a tomographic analysis which consists in measuring the angular correlation of pairs of galaxies in many redshift bins. This tomographic approach allows to compensate the low resolution of the redshift of a photometric redshift, compared to the spectroscopic redshift, by the high number of observed galaxies. On the other hand, it is possible to improve the photometric redshift, also called photo-z, by calibrating the photo-z of a large sample of galaxies whose spectroscopic redshift is known.

The subject of this internship will be to study, develop and test methods for calibrating the Euclid photo-z from a sample of preselected galaxies that have been observed in both photometric and spectrometric modes of the NISP instrument. The candidate will test these methods on the Euclid FlagShip simulation, which is an N-Body simulation of an LCDM Universe containing more than 3 million objects. This internship could be pursued on a thesis on the same subject.

<strong>Keywords :</strong>

Cosmology, Galaxy Clusturing, BAO, Data Analyses, EUCLID, NISP, Photometry, Spectroscopy, Simulation

<strong>Applicant profile :</strong>

Candidates should follow a Master 2 in fundamental physics or astrophysics. Candidates should shows interest in cosmology and machine learning tools. Programming skills (python, C++), strong motivation, ability to work in teams are highly recommanded.

Candidates should by sending their CV and motivation letter as well as grades (Licence, M1 as well as their M2 if available) to both and