Chaos and variance in galaxy formation

B. W. Keller, J. W. Wadsley, L. Wang, J. M.D. Kruijssen

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

The evolution of galaxies is governed by equations with chaotic solutions: gravity and compressible (magneto-)hydrodynamics. While this microscale chaos and stochasticity has been well studied, it is poorly understood how it couples to macroscale properties examined in simulations of galaxy formation. In this paper, we use tiny perturbations introduced by floating-point round-off, random number generators, and seemingly trivial differences in algorithmic behaviour as seeds for chaotic behaviour. These can ultimately grow to produce non-trivial differences in star formation histories, circumgalactic medium properties, and the distribution of stellar mass. We examine the importance of stochasticity due to discreteness noise, variations in merger timings, and how self-regulation moderates the effects of this stochasticity. We show that chaotic variations in stellar mass can be suppressed through gas exhaustion, or be maintained at a roughly constant variance through stellar feedback. We also find that galaxy mergers are critical points from which large (as much as a factor of 2) variations can grow in global quantities such as the total stellar mass. These variations can grow and persist for Gyr before regressing towards the mean. These results show that detailed comparisons of simulations require serious consideration of the magnitude of effects compared to run-to-run chaotic variation, and may significantly complicate interpreting the impact of different physical models. Understanding the results of simulations require us to understand that the process of simulation is not a mapping of an infinitesimal point in configuration space to another, final infinitesimal point. Instead, simulations map a point in a space of possible initial conditions points to a volume of possible final states.

Original languageEnglish
Pages (from-to)2244-2261
Number of pages18
JournalMonthly Notices of the Royal Astronomical Society
Volume482
Issue number2
DOIs
Publication statusPublished - 11 Jan 2019

Fingerprint

galactic evolution
chaotic dynamics
chaos
stochasticity
stellar mass
simulation
merger
galaxies
exhaustion
random numbers
microbalances
floating
star formation
seeds
critical point
generators
hydrodynamics
time measurement
perturbation
histories

Cite this

Keller, B. W. ; Wadsley, J. W. ; Wang, L. ; Kruijssen, J. M.D. / Chaos and variance in galaxy formation. In: Monthly Notices of the Royal Astronomical Society. 2019 ; Vol. 482, No. 2. pp. 2244-2261.
@article{825586d8e3614975a0bb469e9e09327e,
title = "Chaos and variance in galaxy formation",
abstract = "The evolution of galaxies is governed by equations with chaotic solutions: gravity and compressible (magneto-)hydrodynamics. While this microscale chaos and stochasticity has been well studied, it is poorly understood how it couples to macroscale properties examined in simulations of galaxy formation. In this paper, we use tiny perturbations introduced by floating-point round-off, random number generators, and seemingly trivial differences in algorithmic behaviour as seeds for chaotic behaviour. These can ultimately grow to produce non-trivial differences in star formation histories, circumgalactic medium properties, and the distribution of stellar mass. We examine the importance of stochasticity due to discreteness noise, variations in merger timings, and how self-regulation moderates the effects of this stochasticity. We show that chaotic variations in stellar mass can be suppressed through gas exhaustion, or be maintained at a roughly constant variance through stellar feedback. We also find that galaxy mergers are critical points from which large (as much as a factor of 2) variations can grow in global quantities such as the total stellar mass. These variations can grow and persist for Gyr before regressing towards the mean. These results show that detailed comparisons of simulations require serious consideration of the magnitude of effects compared to run-to-run chaotic variation, and may significantly complicate interpreting the impact of different physical models. Understanding the results of simulations require us to understand that the process of simulation is not a mapping of an infinitesimal point in configuration space to another, final infinitesimal point. Instead, simulations map a point in a space of possible initial conditions points to a volume of possible final states.",
keywords = "Galaxies: evolution, Galaxies: formation, Galaxies: star formation, Galaxies: statistics, Methods: numerical",
author = "Keller, {B. W.} and Wadsley, {J. W.} and L. Wang and Kruijssen, {J. M.D.}",
year = "2019",
month = "1",
day = "11",
doi = "10.1093/mnras/sty2859",
language = "English",
volume = "482",
pages = "2244--2261",
journal = "Monthly Notices of the Royal Astronomical Society",
issn = "0035-8711",
publisher = "OXFORD UNIV PRESS UNITED KINGDOM",
number = "2",

}

Chaos and variance in galaxy formation. / Keller, B. W.; Wadsley, J. W.; Wang, L.; Kruijssen, J. M.D.

In: Monthly Notices of the Royal Astronomical Society, Vol. 482, No. 2, 11.01.2019, p. 2244-2261.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Chaos and variance in galaxy formation

AU - Keller, B. W.

AU - Wadsley, J. W.

AU - Wang, L.

AU - Kruijssen, J. M.D.

PY - 2019/1/11

Y1 - 2019/1/11

N2 - The evolution of galaxies is governed by equations with chaotic solutions: gravity and compressible (magneto-)hydrodynamics. While this microscale chaos and stochasticity has been well studied, it is poorly understood how it couples to macroscale properties examined in simulations of galaxy formation. In this paper, we use tiny perturbations introduced by floating-point round-off, random number generators, and seemingly trivial differences in algorithmic behaviour as seeds for chaotic behaviour. These can ultimately grow to produce non-trivial differences in star formation histories, circumgalactic medium properties, and the distribution of stellar mass. We examine the importance of stochasticity due to discreteness noise, variations in merger timings, and how self-regulation moderates the effects of this stochasticity. We show that chaotic variations in stellar mass can be suppressed through gas exhaustion, or be maintained at a roughly constant variance through stellar feedback. We also find that galaxy mergers are critical points from which large (as much as a factor of 2) variations can grow in global quantities such as the total stellar mass. These variations can grow and persist for Gyr before regressing towards the mean. These results show that detailed comparisons of simulations require serious consideration of the magnitude of effects compared to run-to-run chaotic variation, and may significantly complicate interpreting the impact of different physical models. Understanding the results of simulations require us to understand that the process of simulation is not a mapping of an infinitesimal point in configuration space to another, final infinitesimal point. Instead, simulations map a point in a space of possible initial conditions points to a volume of possible final states.

AB - The evolution of galaxies is governed by equations with chaotic solutions: gravity and compressible (magneto-)hydrodynamics. While this microscale chaos and stochasticity has been well studied, it is poorly understood how it couples to macroscale properties examined in simulations of galaxy formation. In this paper, we use tiny perturbations introduced by floating-point round-off, random number generators, and seemingly trivial differences in algorithmic behaviour as seeds for chaotic behaviour. These can ultimately grow to produce non-trivial differences in star formation histories, circumgalactic medium properties, and the distribution of stellar mass. We examine the importance of stochasticity due to discreteness noise, variations in merger timings, and how self-regulation moderates the effects of this stochasticity. We show that chaotic variations in stellar mass can be suppressed through gas exhaustion, or be maintained at a roughly constant variance through stellar feedback. We also find that galaxy mergers are critical points from which large (as much as a factor of 2) variations can grow in global quantities such as the total stellar mass. These variations can grow and persist for Gyr before regressing towards the mean. These results show that detailed comparisons of simulations require serious consideration of the magnitude of effects compared to run-to-run chaotic variation, and may significantly complicate interpreting the impact of different physical models. Understanding the results of simulations require us to understand that the process of simulation is not a mapping of an infinitesimal point in configuration space to another, final infinitesimal point. Instead, simulations map a point in a space of possible initial conditions points to a volume of possible final states.

KW - Galaxies: evolution

KW - Galaxies: formation

KW - Galaxies: star formation

KW - Galaxies: statistics

KW - Methods: numerical

UR - http://www.scopus.com/inward/record.url?scp=85062030300&partnerID=8YFLogxK

U2 - 10.1093/mnras/sty2859

DO - 10.1093/mnras/sty2859

M3 - Article

VL - 482

SP - 2244

EP - 2261

JO - Monthly Notices of the Royal Astronomical Society

JF - Monthly Notices of the Royal Astronomical Society

SN - 0035-8711

IS - 2

ER -