Redshift survey | EPFL Graph Search

In astronomy, a redshift survey is a survey of a section of the sky to measure the redshift of astronomical objects: usually galaxies, but sometimes other objects such as galaxy clusters or quasars.
Using Hubble's law, the redshift can be used to estimate the distance of an object from Earth. By combining redshift with angular position data, a redshift survey maps the 3D distribution of matter within a field of the sky. These observations are used to measure detailed statistical properties of the large-scale structure of the universe. In conjunction with observations of early structure in the cosmic microwave background, these results can place strong constraints on cosmological parameters such as the average matter density and the Hubble constant. Generally the construction of a redshift survey involves two phases: first the selected area of the sky is imaged with a wide-field telescope, then galaxies brighter than a defined limit are selected from the resulting images as non-

Cosmology intertwined: A review of the particle physics, astrophysics, and cosmology associated with the cosmological tensions and anomalies

Richard Irving Anderson, Hsin-Yu Chen, Frédéric Courbin, Fabio Finelli, Mikhail Ivanov, Melissa Joseph, Suresh Kumar, Julien Lesgourgues, Florian Niedermann, Emre Ozulker

The standard Lambda Cold Dark Matter (Lambda CDM) cosmological model provides a good description of a wide range of astrophysical and cosmological data. However, there are a few big open questions that make the standard model look like an approximation to a more realistic scenario yet to be found. In this paper, we list a few important goals that need to be addressed in the next decade, taking into account the current discordances between the different cosmological probes, such as the disagreement in the value of the Hubble constant H-0, the sigma(8)-S-8 tension, and other less statistically significant anomalies. While these discordances can still be in part the result of systematic errors, their persistence after several years of accurate analysis strongly hints at cracks in the standard cosmological scenario and the necessity for new physics or generalisations beyond the standard model. In this paper, we focus on the 5.0 sigma tension between the Planck CMB estimate of the Hubble constant H-0 and the SH0ES collaboration measurements. After showing the H-0 evaluations made from different teams using different methods and geometric calibrations, we list a few interesting new physics models that could alleviate this tension and discuss how the next decade's experiments will be crucial. Moreover, we focus on the tension of the Planck CMB data with weak lensing measurements and redshift surveys, about the value of the matter energy density Omega(m), and the amplitude or rate of the growth of structure (sigma(8), f sigma(8)). We list a few interesting models proposed for alleviating this tension, and we discuss the importance of trying to fit a full array of data with a single model and not just one parameter at a time. Additionally, we present a wide range of other less discussed anomalies at a statistical significance level lower than the H-0-S-8 tensions which may also constitute hints towards new physics, and we discuss possible generic theoretical approaches that can collectively explain the non-standard nature of these signals. Finally, we give an overview of upgraded experiments and next-generation space missions and facilities on Earth that will be of crucial importance to address all these open questions. (C) 2022 The Author(s). Published by Elsevier B.V.

ELSEVIER2022

Large scale structures around medium mass galaxy clusters at intermediate redshift

François Henri Ambroise Rérat

Theory predicts that galaxies are not randomly distributed in the Universe. They form a complex network of filamentary structures, the Cosmic Web, divided in clusters, groups, filaments and walls. This picture has been confirmed by the large galaxy redshift surveys. Galaxy properties like morphology and star formation rates are strongly influenced by their environment. The most radical transformations are observed in galaxy clusters, located at the intersection of filaments. Nevertheless, the location where the environment starts to play a role and the main physical phenomenon responsible for these changes are still unknown. The aim of this thesis is to determine where and how galaxies are affected by the environment, at local and global scales. We gathered high quality photometry in the 5 optical bands

u

g

r

i

and

z

with MegaCam on the Canada-France-Hawaii Telescope for 3 medium mass galaxy clusters at intermediate redshift, with a spatial extent on the sky plane reaching 8 to 13 times the cluster virial radii. These clusters were selected to represent as much as possible progenitors of clusters in the local Universe. The core of these clusters have rich ancillary data from the ESO Distant Cluster Survey. The redshift and mass ranges of these clusters, combined to the wide field of the observations make this study unique. We computed photometric redshifts to map the galaxy distribution around the clusters. We were able to identify overdense regions forming groups and filaments, unveiling for the first time the large scale structures in such details for this type of clusters. We studied the fraction of galaxies in the red sequence in different environments, namely in the field, filaments and groups. We find that significant quenching processes are already at work in filaments, even at large cluster-centric distances. We also show that the local neighborhood of galaxies has a stronger impact on galaxy colors than the global environment. An optical spectroscopic follow-up with the VIsible MultiObject Spectrograph on the Very Large Telescope confirms our photometric results. In particular, the fraction of galaxies with detected \otwo emission line is smaller with increasing density. We also find that the star formation rate, determined from [OII], is in average weaker in groups and clusters than in lower density environments. This thesis opens new perspectives to study the way galaxies populate the Cosmic Web. Combined to weak-lensing analysis and cosmological simulations, it will allow a deeper understanding of the structure formation and their baryonic content. It is a first step before extending the results to much larger samples, with the help of the upcoming all-sky cosmological surveys such as Euclid or the Square Kilometer Array.

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