In Space Science Reviews
http://arxiv.org/abs/1504.05456

For a PDF version of the article, click here.

GALAXY ALIGNMENTS: AN OVERVIEW

Benjamin Joachimi, Marcello Cacciato, Thomas D. Kitching, Adrienne Leonard, Rachel Mandelbaum, Björn Malte Schäfer, Cristóbal Sifón, Henk Hoekstra, Alina Kiessling, Donnacha Kirk, Anais Rassat


1 Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
2 Leiden Observatory, Leiden University, PO Box 9513, 2300 RA, Leiden, the Netherlands
3 Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey RH5 6NT, UK
4 McWilliams Center for Cosmology, Department of Physics, Carnegie Mellon University, Pittsburgh, PA 15213, USA
5 Zentrum für Astronomie der Universität Heidelberg, Astronomisches Recheninstitut, Philosophenweg 12, 69120 Heidelberg, Germany
6 Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA, 91109, USA
7 Laboratoire d'astrophysique (LASTRO), Ecole Polytechnique Fédérale de Lausanne (EPFL), Observatoire de Sauverny, CH-1290 Versoix, Switzerland


Abstract: The alignments between galaxies, their underlying matter structures, and the cosmic web constitute vital ingredients for a comprehensive understanding of gravity, the nature of matter, and structure formation in the Universe. We provide an overview on the state of the art in the study of these alignment processes and their observational signatures, aimed at a non-specialist audience. The development of the field over the past one hundred years is briefly reviewed. We also discuss the impact of galaxy alignments on measurements of weak gravitational lensing, and discuss avenues for making theoretical and observational progress over the coming decade.

Keywords: galaxies: evolution; galaxies: haloes; galaxies: interactions; large-scale structure of Universe; gravitational lensing: weak


Table of Contents

INTRODUCTION

FUNDAMENTALS
A primer on galaxy formation and evolution
A primer on weak gravitational lensing
Tidal alignment theory

DEVELOPMENTS OF THE TWENTIETH CENTURY
The very first works: 1914-1926
A second wave: 1938-1958
A case study: alignments in the Palomar Sky Survey
More recent observational works
Early Tidal Torque Theory
More recent theoretical and numerical progress

INTRA-HALO ALIGNMENTS
Alignment of the central galaxy with its halo
Alignment of satellite galaxy shapes

INTER-HALO AND LARGE-SCALE STRUCTURE ALIGNMENTS
Alignments between galaxy clusters
Alignments with filaments
Alignments with sheets and void surfaces

GALAXY ALIGNMENTS WITH THE MATTER DENSITY FIELD
General observational studies
Early-type galaxies
Late-type galaxies
Alternative alignment mechanisms

IMPACT ON COSMOLOGY

QUO VADIS?

REFERENCES

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