Concentrations of dark haloes emerge from their merger histories

ABSTRACT The concentration parameter is a key characteristic of a dark matter halo that conveniently connects the halo’s present-day structure with its assembly history. Using ‘Dark Sky’, a suite of cosmological N-body simulations, we investigate how halo concentration evolves with time and emerges from the mass assembly history. We also explore the origin of the scatter in the relation between concentration and assembly history. We show that the evolution of halo concentration has two primary modes: (1) smooth increase due to pseudo-evolution; and (2) intense responses to physical merger events. Merger events induce lasting and substantial changes in halo structures, and we observe a universal response in the concentration parameter. We argue that merger events are a major contributor to the uncertainty in halo concentration at fixed halo mass and formation time. In fact, even haloes that are typically classified as having quiescent formation histories experience multiple minor mergers. These minor mergers drive small deviations from pseudo-evolution, which cause fluctuations in the concentration parameters and result in effectively irreducible scatter in the relation between concentration and assembly history. Hence, caution should be taken when using present-day halo concentration parameter as a proxy for the halo assembly history, especially if the recent merger history is unknown.

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Double X/Peanut Structures in Barred Galaxies – Insights from an N–body Simulation

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3814 ◽

2020 ◽

Author(s):

Bogdan C Ciambur ◽

Francesca Fragkoudi ◽

Sergey Khoperskov ◽

Paola Di Matteo ◽

Françoise Combes

Keyword(s):

Dark Matter ◽

Milky Way ◽

Large Fraction ◽

Formation Time ◽

Dark Matter Halo ◽

Barred Galaxies ◽

Pattern Speed ◽

Nearby Galaxies ◽

Dynamical Instabilities ◽

Bow Tie

Abstract Boxy, peanut– or X–shaped “bulges” are observed in a large fraction of barred galaxies viewed in, or close to, edge-on projection, as well as in the Milky Way. They are the product of dynamical instabilities occurring in stellar bars, which cause the latter to buckle and thicken vertically. Recent studies have found nearby galaxies that harbour two such features arising at different radial scales, in a nested configuration. In this paper we explore the formation of such double peanuts, using a collisionless N–body simulation of a pure disc evolving in isolation within a live dark matter halo, which we analyse in a completely analogous way to observations of real galaxies. In the simulation we find a stable double configuration consisting of two X/peanut structures associated to the same galactic bar – rotating with the same pattern speed – but with different morphology, formation time, and evolution. The inner, conventional peanut-shaped structure forms early via the buckling of the bar, and experiences little evolution once it stabilises. This feature is consistent in terms of size, strength and morphology, with peanut structures observed in nearby galaxies. The outer structure, however, displays a strong X, or “bow-tie”, morphology. It forms just after the inner peanut, and gradually extends in time (within 1 to 1.5 Gyr) to almost the end of the bar, a radial scale where ansae occur. We conclude that, although both structures form, and are dynamically coupled to, the same bar, they are supported by inherently different mechanisms.

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A systematic search for galaxy proto-cluster cores at z ∼ 2

Proceedings of the International Astronomical Union ◽

10.1017/s1743921320001933 ◽

2019 ◽

Vol 15 (S359) ◽

pp. 166-167

Author(s):

Makoto Ando ◽

Kazuhiro Shimasaku ◽

Rieko Momose

Keyword(s):

Dark Matter ◽

Galaxy Formation ◽

Clustering Analysis ◽

Mass Function ◽

Stellar Mass ◽

Dark Matter Halo ◽

Massive Galaxies ◽

The Galaxy ◽

Mass Assembly ◽

Cluster Cores

AbstractA proto-cluster core is the most massive dark matter halo (DMH) in a given proto-cluster. To reveal the galaxy formation in core regions, we search for proto-cluster cores at z ˜ 2 in ˜1.5deg2 of the COSMOS field. Using pairs of massive galaxies (log (M*/Mʘ) ≥ 11) as tracers of cores, we find 75 candidate cores. A clustering analysis and the extended Press-Schechter model show that their descendant mass at z = 0 is consistent with Fornax-like or Virgo-like clusters. Moreover, using the IllustrisTNG simulation, we confirm that pairs of massive galaxies are good tracers of DMHs massive enough to be regarded as proto-cluster cores. We then derive the stellar mass function and the quiescent fraction for member galaxies of the 75 candidate cores. We find that stellar mass assembly and quenching are accelerated as early as z ˜ 2 in proto-cluster cores.

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WHAT DO DARK MATTER HALO PROPERTIES TELL US ABOUT THEIR MASS ASSEMBLY HISTORIES?

The Astrophysical Journal ◽

10.1088/0004-637x/757/1/102 ◽

2012 ◽

Vol 757 (1) ◽

pp. 102 ◽

Cited By ~ 20

Author(s):

Anson W. C. Wong ◽

James E. Taylor

Keyword(s):

Dark Matter ◽

Dark Matter Halo ◽

Mass Assembly

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The Dekel-Zhao profile: a mass-dependent dark-matter density profile with flexible inner slope and analytic potential, velocity dispersion, and lensing properties

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2790 ◽

2020 ◽

Vol 499 (2) ◽

pp. 2912-2933

Author(s):

Jonathan Freundlich ◽

Fangzhou Jiang ◽

Avishai Dekel ◽

Nicolas Cornuault ◽

Omry Ginzburg ◽

...

Keyword(s):

Dark Matter ◽

Galaxy Evolution ◽

Galaxy Formation ◽

Density Profile ◽

Velocity Dispersion ◽

Dark Matter Halo ◽

Gravitational Lenses ◽

Concentration Parameter ◽

Mass Dependent ◽

Potential Velocity

ABSTRACT We explore a function with two shape parameters for the dark-matter halo density profile subject to baryonic effects, which is a special case of the general Zhao family of models applied to simulated dark-matter haloes by Dekel et al. This profile has variable inner slope and concentration parameter, and analytic expressions for the gravitational potential, velocity dispersion, and lensing properties. Using the Numerical Investigation of a Hundred Astrophysical Objects cosmological simulations, we find that it provides better fits than the Einasto profile and the generalized NFW profile with variable inner slope, in particular towards the halo centres. We show that the profile parameters are correlated with the stellar-to-halo mass ratio Mstar/Mvir. This defines a mass-dependent density profile describing the average dark-matter profiles in all galaxies, which can be directly applied to observed rotation curves of galaxies, gravitational lenses, and semi-analytic models of galaxy formation or satellite–galaxy evolution. The effect of baryons manifests itself by a significant flattening of the inner density slope and a 20 per cent decrease of the concentration parameter for Mstar/Mvir = 10−3.5–10−2, corresponding to $M_{\rm star} \!\sim \! 10^{7-10}\, \mathrm{ M}_\odot$. The accuracy by which this profile fits simulated galaxies is similar to certain multiparameter mass-dependent profiles, but its fewer parameters and analytic nature make it most desirable for many purposes.

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Equilibrium initial data for luminous matter on top of a BEC dark matter halo

Journal of Physics Conference Series ◽

10.1088/1742-6596/1010/1/012004 ◽

2018 ◽

Vol 1010 ◽

pp. 012004

Author(s):

J. A. González ◽

F. S. Guzmán

Keyword(s):

Dark Matter ◽

Initial Data ◽

Dark Matter Halo ◽

Luminous Matter

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Two-component galaxy models with a central BH – II. The ellipsoidal case

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3338 ◽

2020 ◽

Vol 500 (1) ◽

pp. 1054-1070

Author(s):

Luca Ciotti ◽

Antonio Mancino ◽

Silvia Pellegrini ◽

Azadeh Ziaee Lorzad

Keyword(s):

Dark Matter ◽

Stellar Dynamics ◽

Azimuthal Velocity ◽

Dark Matter Halo ◽

Gas Flows ◽

Total Density ◽

Density Distributions ◽

Stellar Component ◽

Two Component ◽

Analytical Formulae

ABSTRACT Recently, two-component spherical galaxy models have been presented, where the stellar profile is described by a Jaffe law, and the total density by another Jaffe law, or by an r−3 law at large radii. We extend these two families to their ellipsoidal axisymmetric counterparts: the JJe and J3e models. The total and stellar density distributions can have different flattenings and scale lengths, and the dark matter halo is defined by difference. First, the analytical conditions required to have a nowhere negative dark matter halo density are derived. The Jeans equations for the stellar component are then solved analytically, in the limit of small flattenings, also in the presence of a central BH. The azimuthal velocity dispersion anisotropy is described by the Satoh k-decomposition. Finally, we present the analytical formulae for velocity fields near the centre and at large radii, together with the various terms entering the virial theorem. The JJe and J3e models can be useful in a number of theoretical applications, e.g. to explore the role of the various parameters (flattening, relative scale lengths, mass ratios, rotational support) in determining the behaviour of the stellar kinematical fields before performing more time-expensive integrations with specific galaxy models, to test codes of stellar dynamics and in numerical simulations of gas flows in galaxies.

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Brightest cluster galaxies: the centre can(not?) hold

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3286 ◽

2020 ◽

Vol 500 (1) ◽

pp. 310-318

Author(s):

Roberto De Propris ◽

Michael J West ◽

Felipe Andrade-Santos ◽

Cinthia Ragone-Figueroa ◽

Elena Rasia ◽

...

Keyword(s):

Dark Matter ◽

Local Environment ◽

Major Axis ◽

Theoretical Models ◽

Dark Matter Halo ◽

Gas Distribution ◽

X Ray ◽

Cluster Galaxies ◽

Peculiar Velocities ◽

Brightest Cluster Galaxies

ABSTRACT We explore the persistence of the alignment of brightest cluster galaxies (BCGs) with their local environment. We find that a significant fraction of BCGs do not coincide with the centroid of the X-ray gas distribution and/or show peculiar velocities (they are not at rest with respect to the cluster mean). Despite this, we find that BCGs are generally aligned with the cluster mass distribution even when they have significant offsets from the X-ray centre and significant peculiar velocities. The large offsets are not consistent with simple theoretical models. To account for these observations BCGs must undergo mergers preferentially along their major axis, the main infall direction. Such BCGs may be oscillating within the cluster potential after having been displaced by mergers or collisions, or the dark matter halo itself may not yet be relaxed.

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CONSTRAINTS ON THE SHAPE OF THE MILKY WAY DARK MATTER HALO FROM JEANS EQUATIONS APPLIED TO SLOAN DIGITAL SKY SURVEY DATA

The Astrophysical Journal ◽

10.1088/2041-8205/758/1/l23 ◽

2012 ◽

Vol 758 (1) ◽

pp. L23 ◽

Cited By ~ 14

Author(s):

Sarah R. Loebman ◽

Željko Ivezić ◽

Thomas R. Quinn ◽

Fabio Governato ◽

Alyson M. Brooks ◽

...

Keyword(s):

Dark Matter ◽

Survey Data ◽

Milky Way ◽

Sloan Digital Sky Survey ◽

Dark Matter Halo ◽

Sky Survey

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The Dark Matter Halo Density Profile, Spiral Arm Morphology, and Supermassive Black Hole Mass of M33

ISRN Astronomy and Astrophysics ◽

10.5402/2011/725697 ◽

2011 ◽

Vol 2011 ◽

pp. 1-8 ◽

Cited By ~ 6

Author(s):

Marc S. Seigar

Keyword(s):

Black Hole ◽

Dark Matter ◽

Density Profile ◽

Pitch Angle ◽

Rotation Curve ◽

Dark Matter Halo ◽

Black Hole Mass ◽

Supermassive Black Hole ◽

Virial Mass ◽

Spiral Arm

We investigate the dark matter halo density profile of M33. We find that the HI rotation curve of M33 is best described by an NFW dark matter halo density profile model, with a halo concentration of and a virial mass of . We go on to use the NFW concentration of M33, along with the values derived for other galaxies (as found in the literature), to show that correlates with both spiral arm pitch angle and supermassive black hole mass.

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