Angular Momentum Growth around Local Density Maxima

We have calculated the growth of angular momentum about local density maxima at early epochs. We find that high peaks experience higher torques than low peaks, counteracting the short collapse time during which the high peaks can acquire angular momentum. Which effect is dominant depends on the perturbation power spectrum: for power spectra characteristic of both cold dark matter and hot dark matter, the effects nearly cancel, and the total angular momentum acquired by a collapsing object is almost independent of the height of the peak. Furthermore, the distributions of angular momenta acquired by collapsing protosystems are extremely broad, for all power spectra, far exceeding any modest differences between peaks of different height.These results indicate that it is not possible to account for the systematic differences in angular momentum properties of disk and elliptical galaxies simply by postulating that the latter arise from fluctuations of greater overdensity, contrary to some recent suggestions. The figure shows the probability distributions for the final angular momentum acquired by peaks of dimensionless height 1–4, for a power spectrum similar to cold dark matter. A fuller account of this work has been submitted to MNRAS.

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The lensing properties of subhaloes in massive elliptical galaxies in sterile neutrino cosmologies

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz3068 ◽

2019 ◽

Vol 491 (1) ◽

pp. 1295-1310 ◽

Cited By ~ 4

Author(s):

Giulia Despali ◽

Mark Lovell ◽

Simona Vegetti ◽

Robert A Crain ◽

Benjamin D Oppenheimer

Keyword(s):

Dark Matter ◽

Power Spectrum ◽

Galaxy Formation ◽

Cold Dark Matter ◽

Distribution Density ◽

Sterile Neutrino ◽

Power Spectra ◽

Mass Function ◽

Elliptical Galaxies ◽

Hydrodynamical Simulations

ABSTRACT We use high-resolution hydrodynamical simulations run with the EAGLE model of galaxy formation to study the differences between the properties of – and subsequently the lensing signal from – subhaloes of massive elliptical galaxies at redshift 0.2, in Cold and Sterile Neutrino (SN) Dark Matter models. We focus on the two 7 keV SN models that bracket the range of matter power spectra compatible with resonantly produced SN as the source of the observed 3.5 keV line. We derive an accurate parametrization for the subhalo mass function in these two SN models relative to cold dark matter (CDM), as well as the subhalo spatial distribution, density profile, and projected number density and the dark matter fraction in subhaloes. We create mock lensing maps from the simulated haloes to study the differences in the lensing signal in the framework of subhalo detection. We find that subhalo convergence is well described by a lognormal distribution and that signal of subhaloes in the power spectrum is lower in SN models with respect to CDM, at a level of 10–80 per cent, depending on the scale. However, the scatter between different projections is large and might make the use of power spectrum studies on the typical scales of current lensing images very difficult. Moreover, in the framework of individual detections through gravitational imaging a sample of ≃30 lenses with an average sensitivity of $M_{\rm {sub}} = 5 \times 10^{7}\, {\rm M}_{\odot}$ would be required to discriminate between CDM and the considered sterile neutrino models.

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The anisotropy of the power spectrum in periodic cosmological simulations

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab874 ◽

2021 ◽

Vol 503 (4) ◽

pp. 5638-5645

Author(s):

Gábor Rácz ◽

István Szapudi ◽

István Csabai ◽

László Dobos

Keyword(s):

Dark Matter ◽

Power Spectrum ◽

Large Scale ◽

Cold Dark Matter ◽

Initial Conditions ◽

Power Spectra ◽

Cosmological Simulations ◽

Spherical Collapse ◽

Lower Amplitude ◽

Hydrodynamical Simulations

ABSTRACT The classical gravitational force on a torus is anisotropic and always lower than Newton’s 1/r2 law. We demonstrate the effects of periodicity in dark matter only N-body simulations of spherical collapse and standard Lambda cold dark matter (ΛCDM) initial conditions. Periodic boundary conditions cause an overall negative and anisotropic bias in cosmological simulations of cosmic structure formation. The lower amplitude of power spectra of small periodic simulations is a consequence of the missing large-scale modes and the equally important smaller periodic forces. The effect is most significant when the largest mildly non-linear scales are comparable to the linear size of the simulation box, as often is the case for high-resolution hydrodynamical simulations. Spherical collapse morphs into a shape similar to an octahedron. The anisotropic growth distorts the large-scale ΛCDM dark matter structures. We introduce the direction-dependent power spectrum invariant under the octahedral group of the simulation volume and show that the results break spherical symmetry.

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A Model for the Sequence of Elliptical Galaxies

Symposium - International Astronomical Union ◽

10.1017/s0074180900150545 ◽

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.

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Anti-symmetric clustering signals in the observed power spectrum

Journal of Cosmology and Astroparticle Physics ◽

10.1088/1475-7516/2021/12/003 ◽

2021 ◽

Vol 2021 (12) ◽

pp. 003

Author(s):

José Fonseca ◽

Chris Clarkson

Keyword(s):

Dark Matter ◽

Power Spectrum ◽

Euler Equation ◽

Large Scale ◽

Signal To Noise Ratio ◽

Power Spectra ◽

Large Scale Structure ◽

Scale Structure ◽

Signal To Noise ◽

Peculiar Velocities

Abstract In this paper, we study how to directly measure the effect of peculiar velocities in the observed angular power spectra. We do this by constructing a new anti-symmetric estimator of Large Scale Structure using different dark matter tracers. We show that the Doppler term is the major component of our estimator and we show that we can measure it with a signal-to-noise ratio up to ∼ 50 using a futuristic SKAO HI galaxy survey. We demonstrate the utility of this estimator by using it to provide constraints on the Euler equation.

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Impact of dark matter models on the EoR 21-cm signal bispectrum

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1768 ◽

2020 ◽

Vol 497 (3) ◽

pp. 2941-2953 ◽

Cited By ~ 1

Author(s):

Anchal Saxena ◽

Suman Majumdar ◽

Mohd Kamran ◽

Matteo Viel

Keyword(s):

Dark Matter ◽

Structure Formation ◽

Cold Dark Matter ◽

Power Spectra ◽

Neutral Hydrogen ◽

Cosmic Time ◽

Lower Number ◽

Neutral Fraction ◽

Small Scales ◽

Low Mass

ABSTRACT The nature of dark matter sets the timeline for the formation of first collapsed haloes and thus affects the sources of reionization. Here, we consider two different models of dark matter: cold dark matter (CDM) and thermal warm dark matter (WDM), and study how they impact the epoch of reionization (EoR) and its 21-cm observables. Using a suite of simulations, we find that in WDM scenarios, the structure formation on small scales gets suppressed, resulting in a smaller number of low-mass dark matter haloes compared to the CDM scenario. Assuming that the efficiency of sources in producing ionizing photons remains the same, this leads to a lower number of total ionizing photons produced at any given cosmic time, thus causing a delay in the reionization process. We also find visual differences in the neutral hydrogen (H i) topology and in 21-cm maps in case of the WDM compared to the CDM. However, differences in the 21-cm power spectra, at the same neutral fraction, are found to be small. Thus, we focus on the non-Gaussianity in the EoR 21-cm signal, quantified through its bispectrum. We find that the 21-cm bispectra (driven by the H i topology) are significantly different in WDM models compared to the CDM, even for the same mass-averaged neutral fractions. This establishes that the 21-cm bispectrum is a unique and promising way to differentiate between dark matter models, and can be used to constrain the nature of the dark matter in the future EoR observations.

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Calibration of the angular momenta of the minor planets in the solar system

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834196 ◽

2019 ◽

Vol 630 ◽

pp. A68 ◽

Cited By ~ 1

Author(s):

Jian Li ◽

Zhihong Jeff Xia ◽

Liyong Zhou

Keyword(s):

Angular Momentum ◽

Solar System ◽

Total Angular Momentum ◽

Physical Parameters ◽

Minor Planets ◽

The Sun ◽

Relative Angle ◽

Angular Momenta ◽

Dwarf Planets ◽

Invariable Plane

Aims. We aim to determine the relative angle between the total angular momentum of the minor planets and that of the Sun-planets system, and to improve the orientation of the invariable plane of the solar system. Methods. By utilizing physical parameters available in public domain archives, we assigned reasonable masses to 718 041 minor planets throughout the solar system, including near-Earth objects, main belt asteroids, Jupiter trojans, trans-Neptunian objects, scattered-disk objects, and centaurs. Then we combined the orbital data to calibrate the angular momenta of these small bodies, and evaluated the specific contribution of the massive dwarf planets. The effects of uncertainties on the mass determination and the observational incompleteness were also estimated. Results. We determine the total angular momentum of the known minor planets to be 1.7817 × 1046 g cm2 s−1. The relative angle α between this vector and the total angular momentum of the Sun-planets system is calculated to be about 14.74°. By excluding the dwarf planets Eris, Pluto, and Haumea, which have peculiar angular momentum directions, the angle α drops sharply to 1.76°; a similar result applies to each individual minor planet group (e.g., trans-Neptunian objects). This suggests that, without these three most massive bodies, the plane perpendicular to the total angular momentum of the minor planets would be close to the invariable plane of the solar system. On the other hand, the inclusion of Eris, Haumea, and Makemake can produce a difference of 1254 mas in the inclination of the invariable plane, which is much larger than the difference of 9 mas induced by Ceres, Vesta, and Pallas as found previously. By taking into account the angular momentum contributions from all minor planets, including the unseen ones, the orientation improvement of the invariable plane is larger than 1000 mas in inclination with a 1σ error of ∼50−140 mas.

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ETHOS – an effective theory of structure formation: formation of the first haloes and their stars

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz766 ◽

2019 ◽

Vol 485 (4) ◽

pp. 5474-5489 ◽

Cited By ~ 6

Author(s):

Mark R Lovell ◽

Jesús Zavala ◽

Mark Vogelsberger

Keyword(s):

Dark Matter ◽

Power Spectrum ◽

Galaxy Formation ◽

Cold Dark Matter ◽

Dwarf Galaxy ◽

Mass Scale ◽

Effective Theory ◽

Matter Power Spectrum ◽

Hydrodynamical Simulations ◽

Stellar Masses

Abstract A cut-off in the linear matter power spectrum at dwarf galaxy scales has been shown to affect the abundance, formation mechanism and age of dwarf haloes, and their galaxies at high and low redshifts. We use hydrodynamical simulations of galaxy formation within the ETHOS framework in a benchmark model that has such a cut-off and that has been shown to be an alternative to the cold dark matter (CDM) model that alleviates its dwarf-scale challenges. We show how galaxies in this model form differently to CDM, on a halo-by-halo basis, at redshifts z ≥ 6. We show that when CDM haloes with masses around the ETHOS half-mode mass scale are resimulated with the ETHOS matter power spectrum, they form with 50 per cent less mass than their CDM counterparts due to their later formation times, yet they retain more of their gas reservoir due to the different behaviour of gas and dark matter during the monolithic collapse of the first haloes in models with a galactic-scale cut-off. As a result, galaxies in ETHOS haloes near the cut-off scale grow rapidly between z = 10 and 6 and by z = 6 end up having very similar stellar masses, higher gas fractions and higher star formation rates relative to their CDM counterparts. We highlight these differences by making predictions for how the number of galaxies with old stellar populations is suppressed in ETHOS for both z = 6 galaxies and for gas-poor Local Group fossil galaxies. Interestingly, we find an age gradient in ETHOS between galaxies that form in high- and low-density environments.

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