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Theses

Des relevés spectroscopiques de galaxies à raies d'émission aux contraintes cosmologiques : d'eBOSS à DESI

Abstract : Spectroscopic galaxy surveys contain a wealth of cosmological information. Acoustic waves that propagated in the primordial Universe left a signature on the matter distribution, called baryon acoustic oscillations (BAO), at a characteristic scale of 150 megaparsecs. Measuring this standard ruler in the distribution of galaxies provides access to the expansion history of the Universe. In addition, redshift measurements of galaxies are sensitive to their peculiar velocities (RSD), allowing to probe the growth rate of structure and test general relativity on large scales. This thesis is dedicated to the power spectrum analysis of BAO and RSD in the sample of 173,736 emission line galaxies (ELGs) of the eBOSS collaboration, at an effective redshift of 0.85. Special care was devoted to validate the implementation of the galaxy power spectrum theoretical model, and to estimate and correct observational systematics, with the help of realistic simulations. The main observational systematics of this sample stem from fluctuations of the galaxy target density with the quality of the photometric sample used for eBOSS, which is an early version of that utilised in the next generation spectroscopic survey DESI. In particular, besides the noticeable fluctuations of the angular density of targets, strong variations in the redshift density with imaging depth were noted - an effect which is usually assumed to be minor. Residual variations of the angular target density were mitigated by suppressing the density contrast above a certain scale, while fluctuations in the radial survey selection function were accounted for by dividing the data set in subsamples of equivalent photometric depth. Doing so, the measured galaxy power spectrum is damped at large scale, which requires to correct the theoretical prediction for the so-called integral constraints, an original work of this thesis that also allowed to improve some techniques of clustering analyses. The RSD and BAO measurements obtained with eBOSS ELGs are combined with the results from the other clustering samples of the SDSS collaboration, and cosmological implications are presented. This manuscript ends with a recap of different observational and analysis systematics hindering the cosmological measurements, and gives ideas to control the systematic budget of future spectroscopic surveys, like DESI.
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Submitted on : Tuesday, January 5, 2021 - 12:25:28 PM
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  • HAL Id : tel-03097372, version 1

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Arnaud De Mattia. Des relevés spectroscopiques de galaxies à raies d'émission aux contraintes cosmologiques : d'eBOSS à DESI. Cosmology and Extra-Galactic Astrophysics [astro-ph.CO]. Université Paris-Saclay, 2020. English. ⟨NNT : 2020UPASP010⟩. ⟨tel-03097372⟩

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