| Title: |
Towards precision galaxy clustering analyses with DESI : addressing incomplete observations and modeling density-split statistics ; Vers une analyse précise de la distribution spatiale des galaxies avec DESI : incomplétude observationnelle et fonctions à deux points par intervalle de densité |
| Authors: |
Pinon, Mathilde |
| Contributors: |
Département de Physique des Particules (ex SPP) (DPhP); Institut de Recherches sur les lois Fondamentales de l'Univers (IRFU); Université Paris-Saclay-Direction de Recherche Fondamentale (CEA) (DRF (CEA)); Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-Direction de Recherche Fondamentale (CEA) (DRF (CEA)); Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA); Université Paris-Saclay; Etienne Burtin; Arnaud De mattia |
| Source: |
https://theses.hal.science/tel-05351815 ; Cosmology and Extra-Galactic Astrophysics [astro-ph.CO]. Université Paris-Saclay, 2025. English. ⟨NNT : 2025UPASP103⟩. |
| Publisher Information: |
CCSD |
| Publication Year: |
2025 |
| Subject Terms: |
Growth rate of structures; General relativity; Dark energy; Galaxies; Density; Cosmology; Taux de croissance des structures; Relativité générale; Énergie noire; Densité; Cosmologie; [PHYS.ASTR.CO]Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO] |
| Description: |
The study of the large-scale structure of the Universe through galaxy surveys is a major tool for testing the standard model of cosmology and improving our understanding of dark energy, dark matter, and primordial inflation. Since 2021, the Dark Energy Spectroscopic Instrument (DESI) has been surveying the sky to measure the redshifts of nearly 50 million galaxies and quasars, and produced the largest map of the Universe ever made. DESI's first year of observations, completed in June 2022, already includes spectra for over 14 million galaxies. This thesis is dedicated to developing methods for analyzing the spatial distribution of galaxies observed by spectroscopic surveys like DESI.Current cosmological analyses mainly rely on two-point statistics (the correlation function and power spectrum). Extracting precise cosmological constraints from observations of millions of galaxies requires careful control of observational biases. DESI collects galaxy spectra using nearly 5000 optical fibers, whose positions are adjusted for each exposure by robotic positioners. A major challenge in DESI data is incompleteness due to fiber assignment: each fiber can only be allocated to one galaxy per exposure, resulting in a systematic loss of observations, particularly in high-density regions.I propose a robust method to correct this bias in two-point statistics, which consists in excluding galaxy pairs with angular separations smaller than the diameter covered by each fiber positioner, and applying the same cut in theoretical models. Using realistic DESI simulations, I show that this method successfully restores unbiased measurements.Beyond observational biases, two-point statistics have a fundamental limitation: they only capture the covariance of the density field at different scales. While primordial density fluctuations are nearly Gaussian, gravitational collapse induces non-linearities that lead to significant non-Gaussianities on small scales, which are not captured by these statistics.To fully exploit the potential of ... |
| Document Type: |
doctoral or postdoctoral thesis |
| Language: |
English |
| Relation: |
NNT: 2025UPASP103 |
| Availability: |
https://theses.hal.science/tel-05351815; https://theses.hal.science/tel-05351815v1/document; https://theses.hal.science/tel-05351815v1/file/150720_PINON_2025_archivage.pdf |
| Rights: |
https://about.hal.science/hal-authorisation-v1/ ; info:eu-repo/semantics/OpenAccess |
| Accession Number: |
edsbas.DA708D79 |
| Database: |
BASE |