Distribution Of Dark Matter Halos Research Articles

Novel constraints on fermionic dark matter from galactic observables I: The Milky Way

We have recently introduced a new model for the distribution of dark matter (DM) in galaxies based on a self-gravitating system of massive fermions at finite temperatures, the Ruffini-Arg\"uelles-Rueda (RAR) model. We show that this model, for fermion masses in the keV range, explains the DM halo of the Galaxy and predicts the existence of a denser quantum core at the center. We demonstrate here that the introduction of a cutoff in the fermion phase-space distribution, necessary to account for the finite Galaxy size, defines a new solution with a central core which represents an alternative to the black hole (BH) scenario for SgrA*. For a fermion mass in the range $mc^2 = 48$ -- $345$~keV, the DM halo distribution is in agreement with the Milky Way rotation curve data, while harbors a dense quantum core of about $4\times10^6 M_\odot$ within the S2-star pericenter.

Emission from the Ionized Gaseous Halos of Low-redshift Galaxies and Their Neighbors

Abstract Using a sample of nearly half a million galaxies, intersected by over 8 million lines of sight from the Sloan Digital Sky Survey Data Release 12, we extend our previous study of the recombination radiation emitted by the gaseous halos of nearby galaxies. We identify an inflection in the radial profile of the Hα+N[ii] radial emission profile at a projected radius of ∼50 kpc and suggest that beyond this radius the emission from ionized gas in spatially correlated halos dominates the profile. We confirm that this is a viable hypothesis using results from a highly simplified theoretical treatment in which the dark matter halo distribution from cosmological simulations is straightforwardly populated with gas. Whether we fit the fraction of halo gas in a cooler (T = 12,000 K), smooth (c = 1) component (0.26 for galaxies with M ⊙ and 0.34 for those with M ⊙) or take independent values of this fraction from published hydrodynamical simulations (0.19 and 0.38, respectively), this model successfully reproduces the radial location and amplitude of the observed inflection. We also observe that the physical nature of the gaseous halo connects to primary galaxy morphology beyond any relationship to the galaxy’s stellar mass and star formation rate. We explore whether the model reproduces behavior related to the central galaxy’s stellar mass, star formation rate, and morphology. We find that it is unsuccessful in reproducing the observations at this level of detail and discuss various shortcomings of our simple model that may be responsible.

Cumulative Neutrino and Gamma-Ray Backgrounds from Halo and Galaxy Mergers

Abstract The merger of dark matter halos and the gaseous structures embedded in them, such as protogalaxies, galaxies, and groups and clusters of galaxies, results in strong shocks that are capable of accelerating cosmic rays (CRs) to ≳10 PeV. These shocks will produce high-energy neutrinos and γ-rays through inelastic pp collisions. In this work, we study the contributions of these halo mergers to the diffuse neutrino flux and to the nonblazar portion of the extragalactic γ-ray background. We formulate the redshift dependence of the shock velocity, galactic radius, halo gas content, and galactic/intergalactic magnetic fields over the dark matter halo distribution up to a redshift z = 10. We find that high-redshift mergers contribute a significant amount of the CR luminosity density, and the resulting neutrino spectra could explain a large part of the observed diffuse neutrino flux above 0.1 PeV up to several PeV. We also show that our model can somewhat alleviate tensions with the extragalactic γ-ray background. First, since a larger fraction of the CR luminosity density comes from high redshifts, the accompanying γ-rays are more strongly suppressed through γγ annihilations with the cosmic microwave background and the extragalactic background light. Second, mildly radiative-cooled shocks may lead to a harder CR spectrum with spectral indices of 1.5 ≲ s ≲ 2.0. Our study suggests that halo mergers, a fraction of which may also induce starbursts in the merged galaxies, can be promising neutrino emitters without violating the existing Fermi γ-ray constraints on the nonblazar component of the extragalactic γ-ray background.

Universal relations with fermionic dark matter

We have recently introduced a new model for the distribution of dark matter (DM) in galaxies, the Ruffini-Argüelles-Rueda (RAR) model, based on a self-gravitating system of massive fermions at finite temperatures. The RAR model, for fermion masses above keV, successfully describes the DM halos in galaxies, and predicts the existence of a denser quantum core towards the center of each configuration. We demonstrate here, for the first time, that the introduction of a cutoff in the fermion phase-space distribution, necessary to account for galaxies finite size and mass, defines a new solution with a compact quantum core which represents an alternative to the central black hole (BH) scenario for SgrA*. For a fermion mass in the range 48keV ≤ mc2 ≤ 345keV, the DM halo distribution fulfills the most recent data of the Milky Way rotation curves while harbors a dense quantum core of 4×106M⊙ within the S2 star pericenter. In particular, for a fermion mass of mc2 ∼ 50keV the model is able to explain the DM halos from typical dwarf spheroidal to normal elliptical galaxies, while harboring dark and massive compact objects from ∼ 103M⊙ tp to 108M⊙ at their respective centers. The model is shown to be in good agreement with different observationally inferred universal relations, such as the ones connecting DM halos with supermassive dark central objects. Finally, the model provides a natural mechanism for the formation of supermassive BHs as heavy as few ∼ 108M⊙. We argue that larger BH masses (few ∼ 109−10M⊙) may be achieved by assuming subsequent accretion processes onto the above heavy seeds, depending on accretion efficiency and environment.

The Velocity Dispersion Function for Quiescent Galaxies in the Local Universe

Abstract We investigate the distribution of central velocity dispersions for quiescent galaxies in the SDSS at 0.03 ≤ z ≤ 0.10. To construct the field velocity dispersion function (VDF), we construct a velocity dispersion complete sample of quiescent galaxies with D n 4000 > 1.5. The sample consists of galaxies with central velocity dispersion larger than the velocity dispersion completeness limit of the SDSS survey. Our VDF measurement is consistent with previous field VDFs for σ > 200 km s−1. In contrast with previous results, the VDF does not decline significantly for σ < 200 km s−1. The field and the similarly constructed cluster VDFs are remarkably flat at low velocity dispersion (σ < 250 km s−1). The cluster VDF exceeds the field for σ > 250 km s−1 providing a measure of the relatively larger number of massive subhalos in clusters. The VDF is a probe of the dark matter halo distribution because the measured central velocity dispersion may be directly proportional to the dark matter velocity dispersion. Thus the VDF provides a potentially powerful test of simulations for models of structure formation.

Dynamical History Of The Local Group In ΛCDM slowromancapii@ − Including External Perturbers In 3D

We attempt to fit the observed radial velocities (RVs) of ${\,{\sim}\,}30$ Local Group (LG) galaxies using a 3D dynamical model of it and its immediate environment within the context of the standard cosmological paradigm, $\Lambda$CDM. This extends and confirms the basic results of our previous axisymmetric investigation of the LG (MNRAS, 459, 2237). We find that there remains a tendency for observed RVs to exceed those predicted by our best-fitting model. The typical mismatch is slightly higher than in our 2D model, with a root mean square value of ${\,{\sim}\,}50$ km/s. Our main finding is that including the 3D distribution of massive perturbing dark matter halos is unlikely to help greatly with the high velocity galaxy problem. Nonetheless, the 2D and 3D results differ in several other ways such as which galaxies' RVs are most problematic and the preferred values of parameters common to both models. The anomalously high RVs of several LG dwarfs may be better explained if the Milky Way (MW) and Andromeda (M31) were once moving much faster than in our models. This would allow LG dwarfs to gain very high RVs via gravitational slingshot encounters with a massive fast-moving galaxy. Such a scenario is possible in some modified gravity theories, especially those which require the MW and M31 to have previously undergone a close flyby. In a $\Lambda$CDM context, however, this scenario is not feasible as the resulting dynamical friction would cause a rapid merger.

Probing scalar tensor theories for gravity in redshift space

We present measurements of the spatial clustering statistics in redshift space of various scalar field modified gravity simulations. We utilise the two-point and the three-point correlation functions to quantify the spatial distribution of dark matter halos within these simulations and thus discern between the models. We compare $\Lambda$CDM simulations to various modified gravity scenarios and find consistency with previous work in terms of 2-point statistics in real and redshift-space. However using higher order statistics such as the three-point correlation function in redshift space we find significant deviations from $\Lambda$CDM hinting that higher order statistics may prove to be a useful tool in the hunt for deviations from General Relativity.

ALIGNMENTS OF DARK MATTER HALOS WITH LARGE-SCALE TIDAL FIELDS: MASS AND REDSHIFT DEPENDENCE

ABSTRACT Large-scale tidal fields estimated directly from the distribution of dark matter halos are used to investigate how halo shapes and spin vectors are aligned with the cosmic web. The major, intermediate, and minor axes of halos are aligned with the corresponding tidal axes, and halo spin axes tend to be parallel with the intermediate axes and perpendicular to the major axes of the tidal field. The strengths of these alignments generally increase with halo mass and redshift, but the dependence is only on the peak height, . The scaling relations of the alignment strengths with the value of ν indicate that the alignment strengths remain roughly constant when the structures within which the halos reside are still in a quasi-linear regime, but decreases as nonlinear evolution becomes more important. We also calculate the alignments in projection so that our results can be compared directly with observations. Finally, we investigate the alignments of tidal tensors on large scales, and use the results to understand alignments of halo pairs separated at various distances. Our results suggest that the coherent structure of the tidal field is the underlying reason for the alignments of halos and galaxies seen in numerical simulations and in observations.

Velocity bias in the distribution of dark matter halos

The standard formalism for the co-evolution of halos and dark matter predicts that any initial halo velocity bias rapidly decays to zero. We argue that, when the purpose is to compute statistics like power spectra etc., the coupling in the momentum conservation equation for the biased tracers must be modified. Our new formulation predicts the constancy in time of any statistical halo velocity bias present in the initial conditions, in agreement with peak theory. We test this prediction by studying the evolution of a conserved halo population in N-body simulations. We establish that the initial simulated halo density and velocity statistics show distinct features of the peak model and, thus, deviate from the simple local Lagrangian bias. We demonstrate, for the first time, that the time evolution of their velocity is in tension with the rapid decay expected in the standard approach.

Multi-fractal analysis and lacunarity spectrum of the dark matter haloes in the SDSS-DR7

The dark matter halo distribution of the nearby universe is used to study the fractal behaviour in the proximate universe. The data, which is based on four volume-limited galaxy samples was obtained by Muñoz-Cuartas and Mueller (2012) from the Seventh Data Release of the Sloan Digital Sky Survey (SDSS-DR7). In order to know the fractal behaviour of the observed universe, from the initial sample which contains 412,468 galaxies and 339,505 dark matter haloes were used as input for the fractal calculations. Using this data we use the sliding-window technique for the dark matter distribution and compute the multi-fractal dimension and the lacunarity spectrum and use it to study its dependence on radial distance in every sample.The transition to homogeneity is not observed in the dark matter halo distribution obtained from the SDSS-DR7 volume-limited galaxy samples; in its place the dark matter halo distribution exhibits a persistent multi-fractal behaviour where the measured dimension does not arrive at the value of the physical dimension of the space, for all structure parameter values of the analysed set, at least up to radial distances of the ordered from 165 Mpc/h from the available centres of each sample. Our results and their implications are discussed in the context of the formation of large-scale structures in the universe.

The same with less: the cosmic web of warm versus cold dark matter dwarf galaxies

We explore fundamental properties of the distribution of low-mass dark matter haloes within the cosmic web using warm dark matter (WDM) and cold dark matter (CDM) cosmological simulations. Using self-abundance-matched mock galaxy catalogues, we show that the distribution of dwarf galaxies in a WDM universe, wherein low-mass halo formation is heavily suppressed, is nearly indistinguishable to that of a CDM universe whose low-mass haloes are not seen because galaxy formation is suppressed below some threshold halo mass. However, if the scatter between dwarf galaxy luminosity and halo properties is large enough, low-mass CDM haloes would sometimes host relatively bright galaxies thereby populating CDM voids with the occasional isolated galaxy and reducing the numbers of completely empty voids. Otherwise, without high mass to light scatter, all mock galaxy clustering statistics that we consider – the auto-correlation function, the numbers and radial profiles of satellites, the numbers of isolated galaxies, and the probability distribution function of small voids – are nearly identical in CDM and WDM. WDM voids are neither larger nor emptier than CDM voids, when constructed from abundance-matched halo catalogues. It is thus a challenge to determine whether the CDM problem of the overabundance of small haloes with respect to the number density of observed dwarf galaxies has a cosmological solution or an astrophysical solution. However, some clues about the dark matter particle and the scatter between the properties of dwarf galaxies and their dark matter halo hosts might be found in the cosmic web of galaxies in future surveys of the local volume.

English

The basis of the nonlinear least square fitting is to fit the nonlinear rotation curve model with the observed rotation curve of the Orion dwarf galaxy. It has been the most powerful tool to study the distribution of dark matter in galaxies where it is used to obtain the proper mass model of a galaxy. In this paper, we present the rotation curve fit of Orion dwarf galaxy, corrected for asymmetric drift by using the gradient method of nonlinear least square. Our results showed an excellent agreement between the mass models of cored halo profile with the observed rotation curve. Thus, we can estimate the value of disk mass, MD; the core radius, r0 and core density, ro of the galaxy with 1-s of uncertainty. We finally indicated the dark matter halo distribution as cored dark matter halo with density, 3.9 × 106MŸ kpc-3.

HORIZON RUN 3: TOPOLOGY AS A STANDARD RULER

We study the Physically Self Bound Cold Dark Matter Halo distribution which we associate with the massive galaxies within the Horizon Run 3 to estimate the accuracy in determination of the cosmological distance scale measured by the topology analysis. We apply the routine "Contour 3D" to 108 Mock Survey of $\pi$ steradians out to redshift z = 0.6, which effectively correspond to the SDSS-III BOSS survey, and compare the topology with that of a Gaussian Random Phase Field. We find that given three separate smoothing lengths $\lambda =$ 15, 21, and 34 $h^{-1}{\rm Mpc}$, the least $\chi^2$ fit genus per unit volume g yields a 1.7 % fractional uncertainty in smoothing length and angular diameter distance to $z = 0.6$. This is an improvement upon former calibrations of and presents a competitive error estimate with next BAO scale techniques. We also present three dimensional graphics of the Horizon Run 3 spherical mock survey to show a wealth of large-scale structures of the universe that are predicted in surveys like BOSS.

Velocity and mass bias in the distribution of dark matter haloes

The non-linear, scale-dependent bias in the mass distribution of galaxies and the underlying dark matter is a key systematic affecting the extraction of cosmological parameters from galaxy clustering. Using 95 million halos from the Millennium-XXL N-body simulation, we find that the mass bias is scale independent only for $k<0.1 h{\rm Mpc}^{-1}$ today ($z=0$) and for $k<0.2 h{\rm Mpc}^{-1}$ at $z=0.7$. We test analytic halo bias models against our simulation measurements and find that the model of Tinker et al. 2005 is accurate to better then 5% at $z=0$. However, the simulation results are better fit by an ellipsoidal collapse model at $z=0.7$. We highlight, for the first time, another potentially serious systematic due to a sampling bias in the halo velocity divergence power spectra which will affect the comparison between observations and any redshift space distortion model which assumes dark matter velocity statistics with no velocity bias. By measuring the velocity divergence power spectra for different sized halo samples, we find that there is a significant bias which increases with decreasing number density. This bias is approximately 20% at $k=0.1h$Mpc$^{-1}$ for a halo sample of number density $\bar{n} = 10^{-3} (h/$Mpc$)^3$ at both $z=0$ and $z=0.7$ for the velocity divergence auto power spectrum. Given the importance of redshift space distortions as a probe of dark energy and the on-going major effort to advance models for the clustering signal in redshift space, our results show this velocity bias introduces another systematic, alongside scale-dependent halo mass bias, which cannot be neglected.

Halo bias in mixed dark matter cosmologies

The large-scale distribution of cold dark matter halos is generally assumed to trace the large-scale distribution of matter. In a universe with multiple types of matter fluctuations, as is the case with massive neutrinos, the relation between the halo field and the matter fluctuations may be more complicated. We develop a method for calculating the bias factor relating fluctuations in the halo number density to fluctuations in the mass density in the presence of multiple fluctuating components of the energy density. In the presence of massive neutrinos we find a small but pronounced feature in the halo bias near the neutrino free-streaming scale. The neutrino feature is a small step with amplitude that increases with halo mass and neutrino mass density. The scale-dependent halo bias lessens the suppression of the small-scale halo power spectrum and should therefore weaken constraints on neutrino mass from the galaxy auto-power spectrum and correlation function. On the other hand, the feature in the bias is itself a novel signature of massive neutrinos that can be studied independently.

Remapping simulated halo catalogues in redshift space

We discuss the extension to redshift space of a rescaling algorithm, designed to alter the effective cosmology of a pre-existing simulated particle distribution or catalogue of dark matter haloes. The rescaling approach was initially developed by Angulo & White and was adapted and applied to halo catalogues in real space in our previous work. This algorithm requires no information other than the initial and target cosmological parameters, and it contains no tuned parameters. It is shown here that the rescaling method also works well in redshift space, and that the rescaled simulations can reproduce the growth rate of cosmological density fluctuations appropriate for the target cosmology. Even when rescaling a grossly non-standard model with Λ = 0 and zero baryons, the redshift-space power spectrum of standard Λ cold dark matter can be reproduced to about 5 per cent error for k < 0.2 h Mpc−1. The ratio of quadrupole-to-monopole power spectra remains correct to the same tolerance up to k = 1 h Mpc−1, provided that the input halo catalogue contains measured internal velocity dispersions.

Semi-numeric simulations of helium reionization and the fluctuating radiation background

Recent He II Lyman-alpha forest observations from 2.0 < z < 3.2 show large fluctuations in the optical depth at z > 2.7. These results point to a fluctuating He-ionizing background, which may be due to the end of helium reionization of this era. We present a fast, semi-numeric procedure to approximate detailed cosmological simulations. We compute the distribution of dark matter halos, ionization state of helium, and density field at z = 3 in broad agreement with recent simulations. Given our speed and flexibility, we investigate a range of ionizing source and active quasar prescriptions. Spanning a large area of parameter space, we find order-of-magnitude fluctuations in the He II ionization rate in the post-reionization regime. During reionization, the fluctuations are even stronger and develop a bimodal distribution, in contrast to semi-analytic models and the hydrogen equivalent. These distributions indicate a low-level ionizing background even at significant He II fractions.

Cosmology with massive neutrinos I: towards a realistic modeling of the relation between matter, haloes and galaxies

By using a suite of large box-size N-body simulations that incorporate massive neutrinos as an extra set of particles, with total masses of 0.15, 0.30, and 0.60 eV, we investigate the impact of neutrino masses on the spatial distribution of dark matter haloes and on the distribution of galaxies within the haloes. We compute the bias between the spatial distribution of dark matter haloes and the overall matter and cold dark matter distributions using statistical tools such as the power spectrum and the two-point correlation function. Overall we find a scale-dependent bias on large scales for the cosmologies with massive neutrinos. In particular, we find that the bias decreases with the scale, being this effect more important for higher neutrino masses and at high redshift. However, our results indicate that the scale-dependence in the bias is reduced if the latter is computed with respect to the cold dark matter distribution only. We find that the value of the bias on large scales is reasonably well reproduced by the Tinker fitting formula once the linear cold dark matter power spectrum is used, instead of the total matter power spectrum. We also investigate whether scale-dependent bias really comes from purely neutrino's effect or from nonlinear gravitational collapse of haloes. For this purpose, we address the Ων-σ8 degeneracy and find that such degeneracy is not perfect, implying that neutrinos imprint a slight scale dependence on the large-scale bias. Finally, by using a simple halo occupation distribution (HOD) model, we investigate the impact of massive neutrinos on the distribution of galaxies within dark matter haloes. We use the main galaxy sample in the Sloan Digital Sky Survey (SDSS) II Data Release 7 to investigate if the small-scale galaxy clustering alone can be used to discriminate among different cosmological models with different neutrino masses. Our results suggest that different choices of the HOD parameters can reproduce the observational measurements relatively well, and we quantify the difference between the values of the HOD parameters between massless and massive neutrino cosmologies.

Note on structure formation from cosmic string wakes

The search for cosmic strings has been of renewed interest with the advent of precision cosmology. In this note we give a quantitative description of the nonlinear matter density fluctuations that can form from ascaling network of cosmic string wakes. Specifically, we compute the distribution of dark matter halos. These halos would possess strong correlations in position space that should have survived until today. We also discuss the challenges involved in their detection due to their small size and the complex dynamics of their formation.

Galaxy stability within a self-interacting dark matter halo

This paper investigates spheroidal galaxies comprising a self-interacting dark matter (SIDM) halo plus de Vaucouleurs stellar distribution. These are coupled only via their shared gravitational field, which is computed consistently from the density profiles. Assuming conservation of mass, momentum and angular momentum, perturbation analyses reveal the galaxy's response to radial disturbance. The modes depend on fundamental dark matter properties, the stellar mass, and the halo's mass and radius. The coupling of stars and dark matter stabilizes some haloes that would be unstable as one-fluid models. However the centrally densest haloes are unstable, causing radial flows of SIDM and stars (sometimes in opposite directions). Depending on the dark microphysics, some highly diffuse haloes are also unstable. Unstable galaxies might shed their outskirts or collapse. Observed elliptical galaxies appear to exist in the safe domain. Halo pulsations are possible. The innermost node of SIDM waves may occur within 10 half-light radii. Induced stellar ripples may also occur at detectable radii if higher overtones are excited. If any SIDM exists, observational skotoseismology of galaxies could probe dark matter (DM) physics, measure the sizes of specific systems, and perhaps help explain peculiar objects (e.g. some shell galaxies, and the growth of red nuggets).