scholarly journals A new calibration method of sub-halo orbital evolution for semi-analytic models

2020 ◽  
Vol 498 (3) ◽  
pp. 3902-3913
Author(s):  
Shengqi Yang ◽  
Xiaolong Du ◽  
Andrew J Benson ◽  
Anthony R Pullen ◽  
Annika H G Peter
Keyword(s):  
Dark Matter ◽  
High Resolution ◽  
Cold Dark Matter ◽  
Maximum Velocity ◽  
Parameter Tuning ◽  
Dynamical Friction ◽  
Dynamical Models ◽  
Non Linear ◽  
Tidal Heating ◽  
Analytic Models

ABSTRACT Understanding the non-linear dynamics of satellite haloes (a.k.a. ‘sub-haloes’) is important for predicting the abundance and distribution of dark matter sub-structures and satellite galaxies, and for distinguishing among microphysical dark matter models using observations. Typically, modelling these dynamics requires large N-body simulations with high resolution. Semi-analytic models can provide a more efficient way to describe the key physical processes such as dynamical friction, tidal mass loss, and tidal heating, with only a few free parameters. In this work, we present a fast Markov chain Monte Carlo fitting approach to explore the parameter space of such a sub-halo non-linear evolution model. We use the dynamical models described in an earlier work and calibrate the models to two sets of high-resolution cold dark matter N-body simulations, ELVIS and Caterpillar. Compared to previous calibrations that used manual parameter tuning, our approach provides a more robust way to determine the best-fitting parameters and their posterior probabilities. We find that jointly fitting for the sub-halo mass and maximum velocity functions can break the degeneracy between tidal stripping and tidal heating parameters, as well as providing better constraints on the strength of dynamical friction. We show that our semi-analytic simulation can accurately reproduce N-body simulations statistics, and that the calibration results for the two sets of N-body simulations agree at 95 per cent confidence level. Dynamical models calibrated in this work will be important for future dark matter sub-structure studies.

scholarly journals Origin of the galaxy morphology

2003 ◽  
Vol 208 ◽  
pp. 431-432
Author(s):  
N. Nakasato
Keyword(s):  
Dark Matter ◽  
Star Formation ◽  
High Resolution ◽  
Cold Dark Matter ◽  
Star Formation History ◽  
The Galaxy ◽  
Particle Hydrodynamics ◽  
History Of ◽  
Analytic Models ◽  
Galaxy Morphology

In the current most plausible Cold Dark Matter (CDM) cosmology, larger halos increase their mass by the progressive mergers of smaller clumps. Due to these progressive merger events, galaxies have formed and evolved. Such merger events could trigger star bursts depending on mass of a merging object. In other words, star formation history reflects the strength of the interaction between a galaxy and merging objects. Also, a several merger events strongly affect the development of the morphology of galaxies as assumed in semi-analytic models. In the most advanced semi-analytic models, N-body simulations of dark matter particles are used to obtain the merging history of halos. By combining the description of radiative cooling, hydrodynamics and star formation with the obtained merging history, such models successfully have explained the various qualitative predictions. Here, we show the results of similar approach but using a fullly numerical model. In contrast to the semi-analytic models, we use our high resolution Smoothed Particle Hydrodynamics (SPH) models. With our SPH code, we try to tackle the problem of the galaxy morphology. We have done a several handful high-resolution SPH simulations and analyzed the merging history of such models. Accordingly, we can see the relation between the obtained morphology and the merging history or other physical properties of the model.

scholarly journals A Model for the Sequence of Elliptical Galaxies

1987 ◽  
Vol 117 ◽  
pp. 367-367
Author(s):  
Rosemary F. G. Wyse ◽  
Bernard J. T. Jones
Keyword(s):  
Dark Matter ◽  
Power Spectrum ◽  
Galaxy Formation ◽  
Cold Dark Matter ◽  
Initial Conditions ◽  
Elliptical Galaxy ◽  
Elliptical Galaxies ◽  
Density Fluctuations ◽  
Analytic Approximation ◽  
Non Linear

We present a simple model for the formation of elliptical galaxies, based on a binary clustering hierarchy of dark matter, the chemical enrichment of the gas at each level being controlled by supernovae. The initial conditions for the non-linear phases of galaxy formation are set by the post-recombination power spectrum of density fluctuations. We investigate two models for this power spectrum - the first is a straightforward power law, |δk|2 ∝ kn, and the second is Peeble's analytic approximation to the emergent spectrum in a universe dominated by cold dark matter. The normalisation is chosen such that on some scale, say M ∼ 1012M⊙, the objects that condense out have properties - radius and velocity dispersion - resembling ‘typical’ galaxies. There is some ambiguity in this due to the poorly determined mass-to-light ratio of a typical elliptical galaxy — we look at two normalisations, σ1D ∼ 350kms−1 and σ1D ∼ 140kms−1. The choice determines which of Compton cooling or hydrogen cooling is more important during the galaxy formation period. The non-linear behaviour of the perturbations is treated by the homogeneous sphere approximation.

scholarly journals The Lyman-α forest as a diagnostic of the nature of the dark matter

2019 ◽  
Vol 489 (3) ◽  
pp. 3456-3471 ◽  
Author(s):  
Antonella Garzilli ◽  
Andrii Magalich ◽  
Tom Theuns ◽  
Carlos S Frenk ◽  
Christoph Weniger ◽  
...  
Keyword(s):  
Dark Matter ◽  
High Temperature ◽  
High Resolution ◽  
Power Spectrum ◽  
Early Universe ◽  
Thermal Effects ◽  
Cold Dark Matter ◽  
Sterile Neutrinos ◽  
Hydrodynamic Simulations ◽  
Very High

ABSTRACT The observed Lyman-α flux power spectrum (FPS) is suppressed on scales below ${\sim} ~ 30\, {\rm km\, s}^{-1}$. This cut-off could be due to the high temperature, T0, and pressure, p0, of the absorbing gas or, alternatively, it could reflect the free streaming of dark matter particles in the early universe. We perform a set of very high resolution cosmological hydrodynamic simulations in which we vary T0, p0, and the amplitude of the dark matter free streaming, and compare the FPS of mock spectra to the data. We show that the location of the dark matter free-streaming cut-off scales differently with redshift than the cut-off produced by thermal effects and is more pronounced at higher redshift. We, therefore, focus on a comparison to the observed FPS at z > 5. We demonstrate that the FPS cut-off can be fit assuming cold dark matter, but it can be equally well fit assuming that the dark matter consists of ∼7 keV sterile neutrinos in which case the cut-off is due primarily to the dark matter free streaming.

scholarly journals Dark Matter Substructure and Dwarf Galactic Satellites

2010 ◽  
Vol 2010 ◽  
pp. 1-21 ◽  
Author(s):  
Andrey Kravtsov
Keyword(s):  
Dark Matter ◽  
Galaxy Formation ◽  
Luminosity Function ◽  
Cold Dark Matter ◽  
Dynamical Friction ◽  
Density Profiles ◽  
Tidal Forces ◽  
Central Regions ◽  
Galactic Satellites ◽  
Virial Mass

A decade ago cosmological simulations of increasingly higher resolution were used to demonstrate that virialized regions of Cold Dark Matter (CDM) halos are filled with a multitude of dense, gravitationally bound clumps. These dark mattersubhalosare central regions of halos that survived strong gravitational tidal forces and dynamical friction during the hierarchical sequence of merging and accretion via which the CDM halos form. Comparisons with observations revealed that there is a glaring discrepancy between abundance of subhalos and luminous satellites of the Milky Way and Andromeda as a function of their circular velocity or bound mass within a fixed aperture. This large discrepancy, which became known as the “substructure” or the “missing satellites” problem, begs for an explanation. In this paper, the author reviews the progress made during the last several years both in quantifying the problem and in exploring possible scenarios in which it could be accommodated and explained in the context of galaxy formation in the framework of the CDM paradigm of structure formation. In particular, he shows that the observed luminosity function, radial distribution, and the remarkable similarity of the inner density profiles of luminous satellites can be understood within hierarchical CDM framework using a simple model in which efficiency of star formation monotonically decreases with decreasing virial mass satellites had before their accretionwithout any actual sharp galaxy formation threshold.

scholarly journals THE STRUCTURE OF COLD DARK MATTER HALOS: RECENT INSIGHTS FROM HIGH RESOLUTION SIMULATIONS

2009 ◽  
Vol 24 (29) ◽  
pp. 2291-2305 ◽  
Author(s):  
MARCEL ZEMP
Keyword(s):  
Dark Matter ◽  
High Resolution ◽  
Structure Formation ◽  
Cold Dark Matter ◽  
Milky Way ◽  
Dark Matter Halos ◽  
General Properties

We review results from recent high resolution cosmological structure formation simulations, namely the Via Lactea I & II and GHALO projects. These simulations study the formation of Milky Way sized objects within a cosmological framework. We discuss the general properties of cold dark matter halos at redshift z = 0 and focus on new insights into the structure of halos we got due to the unprecedented high resolution in these simulations.

scholarly journals Fast galaxy bars continue to challenge standard cosmology

2021 ◽  
Vol 508 (1) ◽  
pp. 926-939
Author(s):  
Mahmood Roshan ◽  
Neda Ghafourian ◽  
Tahere Kashfi ◽  
Indranil Banik ◽  
Moritz Haslbauer ◽  
...  
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Dark Matter Halo ◽  
Dynamical Friction ◽  
Statistical Population ◽  
Barred Galaxies ◽  
Corotation Radius ◽  
Pattern Speeds ◽  
Hydrodynamical Simulations ◽  
Disc Galaxies

ABSTRACT Many observed disc galaxies harbour a central bar. In the standard cosmological paradigm, galactic bars should be slowed down by dynamical friction from the dark matter halo. This friction depends on the galaxy’s physical properties in a complex way, making it impossible to formulate analytically. Fortunately, cosmological hydrodynamical simulations provide an excellent statistical population of galaxies, letting us quantify how simulated galactic bars evolve within dark matter haloes. We measure bar strengths, lengths, and pattern speeds in barred galaxies in state-of-the-art cosmological hydrodynamical simulations of the IllustrisTNG and EAGLE projects, using techniques similar to those used observationally. We then compare our results with the largest available observational sample at redshift z = 0. We show that the tension between these simulations and observations in the ratio of corotation radius to bar length is 12.62σ (TNG50), 13.56σ (TNG100), 2.94σ (EAGLE50), and 9.69σ (EAGLE100), revealing for the first time that the significant tension reported previously persists in the recently released TNG50. The lower statistical tension in EAGLE50 is actually caused by it only having five galaxies suitable for our analysis, but all four simulations give similar statistics for the bar pattern speed distribution. In addition, the fraction of disc galaxies with bars is similar between TNG50 and TNG100, though somewhat above EAGLE100. The simulated bar fraction and its trend with stellar mass both differ greatly from observations. These dramatic disagreements cast serious doubt on whether galaxies actually have massive cold dark matter haloes, with their associated dynamical friction acting on galactic bars.

scholarly journals Giant cold satellites from low-concentration haloes

2019 ◽  
Vol 489 (1) ◽  
pp. L22-L27
Author(s):  
Nicola C Amorisco
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Velocity Dispersion ◽  
Rare Occurrence ◽  
Low Velocity ◽  
Dynamical Mass ◽  
The Past ◽  
Large Size ◽  
Identify Formation ◽  
Tidal Heating

ABSTRACT The dwarf satellite galaxies of the Milky Way Crater II and Antlia II have uncommonly low dynamical mass densities, due to their large size and low velocity dispersion. Previous work have found it difficult to identify formation scenarios within the Λ cold dark matter (ΛCDM) framework and have invoked cored dark matter haloes, processed by tides. I show that the tidal evolution of ΛCDM NFW haloes is richer than previously recognized. In haloes that fall short of the mass–concentration relation, tidal heating causes the innermost regions to expand significantly, resulting in the formation of giant, kinematically cold satellites like Crater II and Antlia II. While these satellites are reaching apocentre, extra-tidal material can cause an even more inflated appearance. If originally underconcentrated, Crater II and Antlia II may well have experienced very little mass loss, as in fact hinted by their observed metallicity. On a cosmological scale, satellites with low dynamical mass densities are not a rare occurrence, but were more frequent in the past. If indeed a satellite of NGC 1052, the same mechanism may similarly have led to the formation of NGC 1052-DF2.

scholarly journals The fate of magnetic fields in colliding galaxies

2010 ◽  
Vol 6 (S274) ◽  
pp. 376-380
Author(s):  
Hanna Kotarba ◽  
Harald Lesch ◽  
Klaus Dolag ◽  
Thorsten Naab
Keyword(s):  
Dark Matter ◽  
High Resolution ◽  
Magnetic Fields ◽  
Structure Formation ◽  
Large Scale ◽  
Cold Dark Matter ◽  
Gravitational Interaction ◽  
Interacting Galaxies ◽  
Galactic Dynamics

AbstractThe evolution and amplification of large-scale magnetic fields in galaxies is investigated by means of high resolution simulations of interacting galaxies. The goal of our project is to consider in detail the role of gravitational interaction of galaxies for the fate of magnetic fields. Since the tidal interaction up to galaxy merging is a basic ingredient of cold-dark matter (CDM) structure formation models we think that our simulations will give important clues for the interplay of galactic dynamics and magnetic fields.

scholarly journals Thin Planes of Satellites in ΛCDM are not kinematically coherent

2016 ◽  
Vol 11 (S321) ◽  
pp. 40-41
Author(s):  
Tobias Buck ◽  
Aaron A. Dutton ◽  
Andrea V. Macciò
Keyword(s):  
Dark Matter ◽  
High Resolution ◽  
Cold Dark Matter ◽  
High Redshift ◽  
Large Fraction ◽  
Dark Matter Halo ◽  
Kinematic Structure ◽  
Andromeda Galaxy ◽  
High Incidence ◽  
The One

Recently it has been shown by Ibata et al. (2013) that a large fraction of the dwarf satellite galaxies found in the PAndAS survey (McConnachie et al. 2009) and orbiting the Andromeda galaxy are surprisingly aligned in a thin, extended, and kinematically coherent planar structure. The presence of such a structure seems to challenge the current Cold Dark Matter paradigm of structure formation (Ibata et al. 2014, Pawlowski et al. 2014), which predicts a more uniform distribution of satellites around central objects. We show that it is possible to obtain a thin, extended, rotating plane of satellites resembling the one in Andromeda in cosmological collisionless simulations based on this model. Our new 21 high-resolution simulations (see Buck et al. 2015) show a correlation between the formation time of the dark matter halo and the thickness of the plane of satellites. Our simulations have a high incidence of satellite planes as thin, extended, and as rich as the one in Andromeda and with a very coherent kinematic structure when we select early forming haloes. By tracking the formation of the satellites in the plane we show that they have mainly been accreted onto the main object along thin dark matter filaments at high redshift (Dekel et al. 2009, Libeskind et al. 2009, 2011). Our results show that the presence of a thin, extended, rotating plane of satellites is not a challenge for the Cold Dark Matter paradigm, but actually supports one of the predictions of this paradigm related to the presence of filaments of dark matter around galaxies at high redshift.

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