Interplay between Dark Matter and Galactic Structure in Disk and Oblate Elliptical Galaxies

We investigate the radial distribution of galaxies within their host dark\nmatter halos by modeling their small-scale clustering, as measured in the Sloan\nDigital Sky Survey. Specifically, we model the Jiang et al. (2011) measurements\nof the galaxy two-point correlation function down to very small projected\nseparations (10 < r < 400 kpc/h), in a wide range of luminosity threshold\nsamples (absolute r-band magnitudes of -18 up to -23). We use a halo occupation\ndistribution (HOD) framework with free parameters that specify both the number\nand spatial distribution of galaxies within their host dark matter halos. We\nassume that the first galaxy in each halo lives at the halo center and that\nadditional satellite galaxies follow a radial density profile similar to the\ndark matter Navarro-Frenk-White (NFW) profile, except that the concentration\nand inner slope are allowed to vary. We find that in low luminosity samples,\nsatellite galaxies have radial profiles that are consistent with NFW. M_r < -20\nand brighter satellite galaxies have radial profiles with significantly steeper\ninner slopes than NFW (we find inner logarithmic slopes ranging from -1.6 to\n-2.1, as opposed to -1 for NFW). We define a useful metric of concentration,\nM_(1/10), which is the fraction of satellite galaxies (or mass) that are\nenclosed within one tenth of the virial radius of a halo. We find that M_(1/10)\nfor low luminosity satellite galaxies agrees with NFW, whereas for luminous\ngalaxies it is 2.5-4 times higher, demonstrating that these galaxies are\nsubstantially more centrally concentrated within their dark matter halos than\nthe dark matter itself. Our results therefore suggest that the processes that\ngovern the spatial distribution of galaxies, once they have merged into larger\nhalos, must be luminosity dependent, such that luminous galaxies become poor\ntracers of the underlying dark matter.\n

This paper examines the crucial role dark matter plays in both the development of galactic structure and the timeline of cosmic evolution. First, it investigates how the masses of dark matter halos regulate the growth rate of supermassive black holes (SMBHs), thereby controlling galactic structure. The halo depth determines gas inflow rates and cooling efficiency, which decides the rate at which SMBHs accrete matter. As feedback from SMBHs in turn influences star formation rates and the stability of galactical structures, this paper discusses the specific outcomes each type of dark matter halo imposes on galactic structure. Then, the paper explores how different dark matter models, such as hot, cold, warm, and lambda cold dark matter, determine whether primordial density fluctuations survived or were erased during early phases of the universes history. The transfer function of each model is identified, then a graphic comparing each respective matter power spectrum, a cosmological parameter derived from the transfer function, is demonstrated. Finally, the paper would compare observational results from SDSS with the scenarios each matter power spectrum predicted and determine the most accurate dark matter model.

The planar arrangement of nearly half the satellite galaxies of M31 has been a source of mystery and speculation since it was discovered. With a growing number of other host galaxies showing these satellite galaxy planes, their stability and longevity have become central to the debate on whether the presence of satellite planes are a natural consequence of prevailing cosmological models, or represent a challenge. Given the dependence of their stability on host halo shape, we look into how a galaxy plane's dark matter environment influences its longevity. An increased number of dark matter subhalos results in increased interactions that hasten the deterioration of an already-formed plane of satellite galaxies in spherical dark halos. The role of total dark matter mass fraction held in subhalos in dispersing a plane of galaxies present non trivial effects on plane longevity as well. But any misalignments of plane inclines to major axes of flattened dark matter halos lead to their lifetimes being reduced to < 3 Gyrs. Distributing > 40% of total dark mass in subhalos in the overall dark matter distribution results in a plane of satellite galaxies that is prone to change through the 5 Gyr integration time period.

In this Chapter, we discuss in a unified way equilibrium points, periodic orbits and their stability, which constitute local concepts of Hamiltonian dynamics together with ordered and chaotic motion, which are the concern of a more global type of analysis. Using the Fermi Pasta Ulam β (FPU − β) model as an example, we study the destabilization properties of some of its simple periodic orbits and connect them to wider aspects of the motion in phase space. We show numerically that the spectrum of positive Lyapunov exponents, characterizing a region of strong chaos, becomes invariant in the thermodynamic limit, verifying that the Kolmogorov-Sinai entropy, defined as the sum of these exponents, is an extensive property of the system. The Chapter ends with an introduction of the smaller alignment index (SALI) and the generalized alignment index (GALI) criteria for distinguishing ordered from chaotic motion.

Geometrical properties of local dynamics in Hamiltonian systems: The Generalized Alignment Index (GALI) method

The elastic scattering between dark matter particles and radiation represents an attractive possibility to solve a number of discrepancies between observations and standard cold dark matter predictions, as the induced collisional damping would imply a suppression of small-scale structures. We consider this scenario and confront it with measurements of the ionization history of the Universe at several redshifts and with recent estimates of the counts of Milky Way satellite galaxies. We derive a conservative upper bound on the dark matter-photon elastic scattering cross section of σγ DM < 8 × 10−10 σT (mDM/GeV) at 95% CL, about one order of magnitude tighter than previous constraints from satellite number counts. Due to the strong degeneracies with astrophysical parameters, the bound on the dark matter-photon scattering cross section derived here is driven by the estimate of the number of Milky Way satellite galaxies. Finally, we also argue that future 21 cm probes could help in disentangling among possible non-cold dark matter candidates, such as interacting and warm dark matter scenarios. Let us emphasize that bounds of similar magnitude to the ones obtained here could be also derived for models with dark matter-neutrino interactions and would be as constraining as the tightest limits on such scenarios.

The mass-to-luminosity ratio of the dwarf satellite galaxies in the Milky Way suggests that these dwarf galaxies may contain substantial dark matter. The dark matter at the dense region such as within or at the vicinity of the centres of these dwarf galaxies may undergo the process of self-annihilation and produce γ-rays as the end product. The satellite borne γ-ray telescope such as Fermi-LAT reported the detection of γ-rays from around 45 Dwarf Spheroidals (dSphs) of Milky Way. In this work, we consider particle dark matter models described in the literature and after studying their phenomenologies, we calculate the γ-ray fluxes from the self-annihilation of the dark matter within the framework of these models in case of each of these 45 dSphs. We then compare the computed results with the observational upper bounds for γ-ray flux reported by Fermi-LAT and Dark Energy Survey for each of the 45 dSphs. The fluxes are calculated by adopting different dark matter density profiles. We then extend similar analysis for the observational upper bounds given by Fermi-LAT for the continuum γ-ray fluxes originating from extragalactic sources.

The satellite galaxies of the Milky Way (MW) are effective probes of the underlying dark matter (DM) substructure, which is sensitive to the nature of the DM particle. In particular, a class of DM models have a power spectrum cut-off on the mass scale of dwarf galaxies and thus predict only small numbers of substructures below the cut-off mass. This makes the MW satellite system appealing to constrain the DM properties: feasible models must produce enough substructure to host the number of observed Galactic satellites. Here, we compare theoretical predictions of the abundance of DM substructure in thermal relic warm DM (WDM) models with estimates of the total satellite population of the MW. This produces conservative robust lower limits on the allowed mass, m th, of the thermal relic WDM particle. As the abundance of satellite galaxies depends on the MW halo mass, we marginalize over the corresponding uncertainties and rule out m th ≤ 2.02 keV at 95 percent confidence independently of assumptions about galaxy formation processes. Modelling some of these — in particular, the effect of reionization, which suppresses the formation of dwarf galaxies — strengthens our constraints on the DM properties and excludes models with m th ≤ 2.02 keV in our fiducial model. We also find that thermal relic models cannot produce enough satellites if the MW halo mass is M 200 ≤ 0.6 × 1012 M ☉, which imposes a lower limit on the MW halo mass in CDM. We address several observational and theoretical uncertainties and discuss how improvements in these will strengthen the DM mass constraints.

We investigate how the orbital evolution and mass distribution of infalling satellite galaxies shape the phase-space and radial distributions of intracluster light (ICL) relative to the underlying cluster dark matter (DM) halo. Using controlled, self-consistent N-body simulations, we follow the tidal stripping and orbital evolution of satellite galaxies as they are accreted into a live cluster halo, systematically varying satellite–to–host mass ratio and orbital circularity. From these experiments, we measure the specific orbital energy and angular momentum of stripped stellar and DM material, finding that stripped stars consistently occupy lower-energy and lower-angular momentum regions of phase-space than stripped DM. The magnitude of this difference increases strongly towards more equal satellite–to–host mass ratios, while dependence on circularity is weak. We construct a predictive model for the phase-space properties of stripped stars and DM from a given infalling satellite population and find that phase-space differences are driven primarily by the characteristic mass of the satellite stellar mass function. The ICL is always more centrally concentrated than the DM, with offset magnitude increasing towards higher characteristic masses. Comparisons with four cosmological hydrodynamical simulations show that, once the satellite stellar mass function is matched, the model reproduces the radial stellar-to-DM density profile offsets to better than inter-simulation scatter. This demonstrates that the radial ICL-DM relationship is largely governed by satellite demographics. With adequate constraints on the infalling satellite population, ICL density profiles can therefore be used as informative tracers of the underlying radial DM distribution in clusters.

Application of the SALI chaos detection method to accelerator mappings

We present a comparison of different numerical techniques for the integration of variational equations. The methods presented can be applied to any autonomous Hamiltonian system whose kinetic energy is quadratic in the generalized momenta, and whose potential is a function of the generalized positions. We apply the various techniques to the well-known H´enon-Heiles system, and use the Smaller Alignment Index (SALI) method of chaos detection to evaluate the percentage of its chaotic orbits. The accuracy and the speed of the integration schemes in evaluating this percentage are used to investigate the numerical efficiency of the various techniques.

view Abstract Citations (62) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Face-on galaxies. Lewis, B. M. Abstract A 21 cm survey of about 200 face-on galaxies using the 305 m Arecibo radio telescope is reported. The narrowest profiles for every morphological type are presented. The data are consistent with an integral velocity dispersion of about 8 km/s in every morphological type. When combined with the results of other studies, the present results indicate that the gas dispersion appears to be a universal number, broadly independent of morphological type, absolute magnitude, and position within a galaxy. Two direct consequences follow from the universality of an isotropic velocity distribution: (1) the 'missing mass' component within galaxies necessarily resides in the halo, and (2) small galaxies may only maintain an H I distribution through galaxy-wide random motions, provided that the appropriate dispersion is the canonical one. Publication: The Astrophysical Journal Pub Date: October 1984 DOI: 10.1086/162474 Bibcode: 1984ApJ...285..453L Keywords: Centimeter Waves; H Lines; Hydrogen Clouds; Interstellar Gas; Radio Galaxies; Spiral Galaxies; Galactic Rotation; Galactic Structure; Kinematics; Mass Distribution; Missing Mass (Astrophysics); Radial Velocity; Spectral Line Width; Velocity Distribution; Astrophysics full text sources ADS | data products SIMBAD (29) NED (13)

The abnormally weighting energy hypothesis consists of assuming that the dark sector of cosmology violates the weak equivalence principle (WEP) on cosmological scales, which implies a violation of the strong equivalence principle for ordinary matter. In this paper, dark energy is shown to result from the violation of WEP by pressureless (dark) matter. This allows us to build a new cosmological framework in which general relativity is satisfied at low scales, as WEP violation depends on the ratio of the ordinary matter over dark matter densities, but at large scales, we obtain a general relativity-like theory with a different value of the gravitational coupling. This explanation is formulated in terms of a tensor-scalar theory of gravitation without WEP for which there exists a revisited convergence mechanism toward general relativity. The consequent dark energy mechanism build upon the anomalous gravity of dark matter (i) does not require any violation of the strong energy condition p<-{rho}c{sup 2}/3, (ii) offers a natural way out of the coincidence problem thanks to the nonminimal couplings to gravitation, (iii) accounts fairly for supernovae data from various simple couplings and with density parameters very close to the ones of the concordance model {lambda}CDM, and therefore suggests anmore » explanation to its remarkable adequacy. Finally, (iv) this mechanism ends up in the future with an Einstein-de Sitter expansion regime once the attractor is reached.« less

Spergel &amp; Steinhardt proposed the possibility that the dark matter particlesare self-interacting, as a solution to two discrepancies between thepredictions of cold dark matter models and the observations: first, theobserved dark matter distribution in some dwarf galaxies has large,constant-density cores, as opposed to the predicted central cusps; and second,small satellites of normal galaxies are much less abundant than predicted. Thedark matter self-interaction would produce isothermal cores in halos, and wouldalso expel the dark matter particles from dwarfs orbiting within large halos.However, another inevitable consequence of the model is that halos shouldbecome spherical once most particles have interacted. Here, I rule out thismodel by the fact that the innermost regions of dark matter halos in massiveclusters of galaxies are elliptical, as shown by gravitational lensing andother observations. The absence of collisions in the lensing cores of massiveclusters implies that any dark matter self-interaction is too weak to haveaffected the observed density profiles in the dark-matter dominated dwarfgalaxies, or to have eased the destruction of dwarf satellites in galactichalos. If $s_x$ is the cross section and $m_x$ the mass of the dark matterparticle, then $s_x/m_x &lt; 10^{-25.5} \\cm^2/\\gev$.

Despite the interest in Dark Matter (DM) searches is currently more focused on underground experiments, a signature of DM annihilation/decay in gamma-rays from space would constitute a smoking gun for its identification. In this contribution, we start with a brief review of the efforts of the ground-based MAGIC Cherenkov telescopes system to detect DM signatures from dwarf satellite galaxies orbiting the Milky Way halo. We then present the recent survey of Segue 1, considered by many as possibly the most DM dominated satellite galaxy known in our galaxy. No significant gamma-ray emission was found above the background in around 30 hours of observation. This is the largest survey ever made on a single dwarf by Cherenkov telescopes. We present a novel analysis that fully takes into account the spectral features of the gamma-ray spectrum of specific DM models in a Supersymmetric scenario. We also discuss the prospects of detection after the Fermi observation of similar objects at lower energies.