Dark Matter Contribution Research Articles

[formula omitted]-Cosmological Boundary Flux Parameter

Efforts to explain the current accelerated expansion of the universe have prompted the investigation of different scenarios characterised by dark energy models. In this study, we explore an extended ωCBFP model, incorporating two commonly used parameterisations of ω(z) in terms of the redshift z: ω(z)=ω0 and ω(z)=ω0+ω1z/(1+z). In this context, the cosmological parameter Λ is directly linked to the dark matter component through a barotropic framework, where Λ acts as the source of ρcdm, characterised by a dimensionless constant λ, and directly dependent on Λω(z)CDM, which is fully defined by a specific ω(z) functional form. Through a statistical analysis, using late-time data of observational Hubble and type Ia Supernovae, we computed the joint best-fit value of the free parameters by means of the affine-invariant MCMC. On the one hand, the ω0CBFP instance shows an unexpected larger Ω0cdm contribution than the current Ω0Λ. Remarkably this outcome has not been previously reported (to our knowledge). On the other hand, in the ω0ω1CBFP example the dark energy component makes up nearly 60% of the total matter-energy at z=0, compared to just 36% for the cold dark matter contribution. This last result aligns more with the conventional ΛCDM model. In both instances there are unusual increases in Ωcdm(z) around z=1; however, these rises are offset by a decrease in Ωb(z).

Imprints of dark matter on the structural properties of minimally deformed compact stars

In this manuscript, we investigate the possibility of constructing anisotropic dark matter compact stars motivated by the Einasto density profile. This work develops analytical solutions for an anisotropic fluid sphere within the framework of the well-known Adler–Finch–Skea metric. This toy model incorporates an anisotropic fluid distribution that includes a dark matter component. We use the minimal geometric deformation scheme within the framework of gravitational decoupling to incorporate anisotropy into the pressure profile of the stellar system. In this context, we model the temporal constituent of the Θ-field sector to characterize the contribution of dark matter within the gravitational matter source. We present an alternative approach to studying anisotropic self-gravitating structures. This approach incorporates additional field sources arising from gravitational decoupling, which act as the dark component. We explicitly verify whether the proposed model satisfies all the requirements for describing realistic compact structures in detail. We conclude that the modeling of the Einasto density model with the Adler–Finch–Skea metric gives rise to the formation of well-behaved and viable astrophysical results that can be employed to model the dark matter stellar configurations.

Dark Matter Distribution in Milky Way analog Galaxies

Our current understanding of how dark matter (DM) is distributed within the Milky Way (MW) halo, particularly in the solar neighborhood, is based on either careful studies of the local stellar orbits, model assumptions on the global shape of the MW halo, or from direct acceleration measurements. In this work, we undertake a study of external galaxies, with the intent of providing insight into the DM distribution in MW-analog galaxies. For this, we carefully select a sample of galaxies similar to the MW, based on maximum atomic hydrogen (H i) rotational velocity ( vmax,HI=200–280 km s−1) and morphological type (Sab–Sbc) criteria. With a need for deep, highly resolved H i, our resulting sample is composed of five galaxies from the VLA Imaging of Virgo in Atomic Gas (VIVA) survey and The H i Nearby Galaxy Survey (THINGS). To perform our baryonic analysis, we use deep mid-IR images at 3.6 and 4.5 μm from the Spitzer Survey of Stellar Structures in Galaxies (S4G). Based on the dynamical three-dimensional modeling software 3D-Based Analysis of Rotating Objects via Line Observations (3D-BAROLO), we construct rotation curves (RCs) and derive the gas and stellar contributions from the galaxy's gaseous and stellar disks' mass surface density profiles. Through a careful decomposition of their RCs into their baryonic (stars, gas) and DM components, we isolate the DM contribution by using a Markov Chain Monte Carlo-based approach. Based on the Sun's location and the MW’s R 25, we define the corresponding location of the solar neighborhood in these systems. We put forward a window for the DM density (ρ dm = 0.21–0.55 GeV cm−3) at these galactocentric distances in our MW analog sample, consistent with the values found for the MW’s local DM density, based on more traditional approaches found in the literature.

The Hunt for Chemical Dark Matter across a River-to-Ocean Continuum.

Thousands of mass peaks emerge during molecular characterization of natural dissolved organic matter (DOM) using ultrahigh-resolution mass spectrometry. While mass peaks assigned to certain molecular formulas have been extensively studied, the uncharacterized mass peaks that represent a significant fraction of organic matter and convey biogenic elements and energy have been previously ignored. In this study, we introduce the term dark DOM (DDOM) for unassigned mass peaks and have explored its characteristics and environmental behaviors using a data set of 38 DOM extracts covering the Yangtze River-to-ocean continuum. We identified a total of 9141 DDOM molecules, which exhibited higher molecular weight and greater diversity than the DOM subset with assigned DOM formulas. Although DDOM contributed a smaller fraction of relative abundance, it significantly impacted the molecular weight and molecular composition of bulk DOM. A portion of DDOM with higher molecular weight was found to increase molecular abundance across the river-to-ocean continuum. These compounds could contain halogenated organic molecules and might have a high potential to contribute to the refractory organic carbon pool. With this study, we underline the contribution of dark matter to the total DOM pool and emphasize that more DDOM research is needed to understand its contribution to global biogeochemical cycles and carbon sequestration.

Orbital Torus Imaging: Acceleration, Density, and Dark Matter in the Galactic Disk Measured with Element Abundance Gradients

Under the assumption of a simple and time-invariant gravitational potential, many Galactic dynamics techniques infer the milky Way’s mass and dark matter distributions from stellar kinematic observations. These methods typically rely on parameterized potential models of the Galaxy and must take into account nontrivial survey selection effects, because they make use of the density of stars in phase space. Large-scale spectroscopic surveys now supply information beyond kinematics in the form of precise stellar label measurements (especially element abundances). These element abundances are known to correlate with orbital actions or other dynamical invariants. Here, we use the Orbital Torus Imaging framework that uses abundance gradients in phase space to map orbits. In many cases these gradients can be measured without detailed knowledge of the selection function. We use stellar surface abundances from the Apache Point Observatory Galactic Evolution Experiment survey combined with kinematic data from the Gaia mission. Our method reveals the vertical (z-direction) orbital structure in the Galaxy and enables empirical measurements of the vertical acceleration field and orbital frequencies in the disk. From these measurements, we infer the total surface mass density, Σ, and midplane volume density, ρ 0, as a function of Galactocentric radius and height. Around the Sun, we find Σ⊙(z=1.1kpc)=72−9+6M⊙pc−2 and ρ⊙(z=0)=0.081−0.009+0.015M⊙pc−3 using the most constraining abundance ratio, [Mg/Fe]. This corresponds to a dark matter contribution in surface density of Σ⊙,DM(z = 1.1 kpc) = 24 ± 4 M ⊙ pc−2, and in total volume mass density of ρ ⊙,DM(z = 0) = 0.011 ± 0.002 M ⊙ pc−3. Moreover, using these mass density values we estimate the scale length of the low-α disk to be h R = 2.24 ± 0.06 kpc.

Constraining self-interacting fermionic dark matter in admixed neutron stars using multimessenger astronomy

ABSTRACT We investigate the structure of admixed neutron stars with a regular hadronic component and a fraction of fermionic self-interacting dark matter. Using two limiting equations of state for the dense baryonic interior, constructed from piecewise generalized polytropes, and an asymmetric self-interacting fermionic dark component, we analyse different scenarios of admixed neutron stars depending on the mass of dark fermions mχ, interaction mediators mϕ, and self-interacting strengths g. We find that the contribution of dark matter to the masses and radii of neutron stars leads to tension with mass estimates of the pulsar J0453+1559, the least massive neutron star, and with the constraints coming from the GW170817 event. We discuss the possibilities of constraining dark matter model parameters g and y ≡ mχ/mϕ, using current existing knowledge on neutron star estimations of mass, radius, and tidal deformability, along with the accepted cosmological dark matter freeze-out values and self-interaction cross-section to mass ratio, σSI/mχ, fitted to explain Bullet, Abell, and dwarf galaxy cluster dynamics. By assuming the most restrictive upper limit, σSI/mχ < 0.1 cm2 g−1, along with dark matter freeze-out range values, the allowed g–y region is 0.01 ≲ g ≲ 0.1, with 0.5 ≲ y ≲ 200. For the first time, the combination of updated complementary restrictions is used to set constraints on self-interacting dark matter.

A Wheeler–DeWitt Quantum Approach to the Branch-Cut Gravitation with Ordering Parameters

In this contribution to the Festschrift for Prof. Remo Ruffini, we investigate a formulation of quantum gravity using the Hořava–Lifshitz theory of gravity, which is General Relativity augmented by counter-terms to render the theory regularized. We are then led to the Wheeler–DeWitt (WDW) equation combined with the classical concepts of the branch-cut gravitation, which contemplates as a new scenario for the origin of the Universe, a smooth transition region between the contraction and expansion phases. Through the introduction of an energy-dependent effective potential, which describes the space-time curvature associated with the embedding geometry and its coupling with the cosmological constant and matter fields, solutions of the WDW equation for the wave function of the Universe are obtained. The Lagrangian density is quantized through the standard procedure of raising the Hamiltonian, the helix-like complex scale factor of branched gravitation as well as the corresponding conjugate momentum to the category of quantum operators. Ambiguities in the ordering of the quantum operators are overcome with the introduction of a set of ordering factors α, whose values are restricted, to make contact with similar approaches, to the integers α=[0,1,2], allowing this way a broader class of solutions for the wave function of the Universe. In addition to a branched universe filled with underlying background vacuum energy, primordial matter and radiation, in order to connect with standard model calculations, we additionally supplement this formulation with baryon matter, dark matter and quintessence contributions. Finally, the boundary conditions for the wave function of the Universe are imposed by assuming the Bekenstein criterion. Our results indicate the consistency of a topological quantum leap, or alternatively a quantum tunneling, for the transition region of the early Universe in contrast to the classic branched cosmology view of a smooth transition.

Tracking the Local Group dynamics by extended gravity

The Local Group (LG) of galaxies, modeled as a two body problem, is sensitive to cosmological contributions like those related to the presence of a cosmological constant Λ into dynamics. Here we study the LG dynamics in the context of Extended Theories of Gravity like f(R) gravity considered as dark energy and dark matter contributions. In the first approach, we perturb the dark energy effect considering a Yukawa-like interaction that naturally emerges from f(R) gravity in the weak field limit. We assume the mass of LG from simulations and, from this, derive constraints on the Yukawa couplings: α<0.581 and mgrav<5.095⋅10−26eV/c2. In the second part, considering a minimal extension of General Relativity, i.e. f(R)∼R1+ϵ, with |ϵ|≪1, we investigate the possibility that it replaces dark matter as a MOND-like theory. We find that there is a value of the parameter β (derived starting from ϵ) which gives a minimal value for the LG mass. Moreover, this particular potential allows to calculate the ratio of dark matter and baryonic matter for the LG to be. We show that this ratio could falsify MOND-like theories.

Kinematics and mass distributions for non-spherical deprojected Sérsic density profiles and applications to multi-component galactic systems

Using kinematics to decompose the mass profiles of galaxies, including the dark matter contribution, often requires parameterization of the baryonic mass distribution based on ancillary information. One such model choice is a deprojected Sérsic profile with an assumed intrinsic geometry. The case of flattened, deprojected Sérsic models has previously been applied to flattened bulges in local star-forming galaxies (SFGs), but can also be used to describe the thick, turbulent disks in distant SFGs. Here, we extend this previous work that derived density (ρ) and circular velocity (vcirc) curves by additionally calculating the spherically-enclosed 3D mass profiles (Msph). Using these profiles, we compared the projected and 3D mass distributions, quantified the differences between the projected and 3D half-mass radii (Re; r1/2, mass, 3D), and compiled virial coefficients relating vcirc(R) and Msph(&lt; r = R) or Mtot. We quantified the differences between mass fraction estimators for multi-component systems, particularly for dark matter fractions (ratio of squared circular velocities versus ratio of spherically enclosed masses), and we considered the compound effects of measuring dark matter fractions at the projected versus 3D half-mass radii. While the fraction estimators produce only minor differences, using different aperture radius definitions can strongly impact the inferred dark matter fraction. As pressure support is important in analyses of gas kinematics (particularly, at high redshifts), we also calculated the self-consistent pressure support correction profiles, which generally predict less pressure support than for the self-gravitating disk case. These results have implications for comparisons between simulation and observational measurements, as well as for the interpretation of SFG kinematics at high redshifts. We have made a set of precomputed tables and the code to calculate the profiles publicly available.

Galactic dark matter effects from purely geometrical aspects of general relativity

We study disk galaxies in the framework of general relativity to focus on the possibility that, even in the low energy limit, there are relevant corrections with respect to the purely Newtonian approach. Our analysis encompasses the model by considering both a low energy expansion and exact solutions, making clear the connection between these different approaches. In particular, we focus on two different limits: the well-known gravitomagnetic analogy and a new limit, called ``strong gravitomagnetism,'' which has corrections in $c$ of the same order as the Newtonian terms. We show that these two limits of the general class of solutions can account for the observed flat velocity profile, which is contrary to what happens using Newtonian models, where a dark matter contribution is required. Hence, we suggest a geometrical origin for a certain amount of dark matter effects.

Nonthermal neutrino-like hot dark matter in light of the S8 tension

The $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ prediction of ${S}_{8}\ensuremath{\equiv}{\ensuremath{\sigma}}_{8}({\mathrm{\ensuremath{\Omega}}}_{m}/0.3{)}^{0.5}$---where ${\ensuremath{\sigma}}_{8}$ is the root mean square of matter fluctuations on an $8\text{ }\text{ }{h}^{\ensuremath{-}1}\text{ }\mathrm{Mpc}$ scale---once calibrated on Planck cosmic microwave background data is $2\ensuremath{-}3\ensuremath{\sigma}$ lower than its direct estimate by a number of weak lensing surveys. In this paper, we explore the possibility that the ``${S}_{8}$ tension'' is due to a fractional contribution of nonthermal hot dark matter (HDM) to the energy density of the Universe leading to a power suppression at small scales in the matter power spectrum. Any HDM model can be characterized by its effective mass ${m}_{\mathrm{sp}}^{\mathrm{eff}}$ and its contribution to the relativistic degrees of freedom at cosmic microwave background decoupling $\mathrm{\ensuremath{\Delta}}{N}_{\mathrm{eff}}$. Taking the specific example of a sterile particle produced from the decay of the inflaton during an early matter-dominated era, we find that the tension can be reduced below $2\ensuremath{\sigma}$ from Planck data only, but it does not favor a nonzero ${{m}_{\mathrm{sp}}^{\mathrm{eff}},\mathrm{\ensuremath{\Delta}}{N}_{\mathrm{eff}}}$. In combination with a measurement of ${S}_{8}$ from $\mathrm{KiDS}1000+\mathrm{BOSS}+2\mathrm{dfLenS}$, the ${S}_{8}$ tension would hint at the existence of a particle of mass ${m}_{\mathrm{sp}}^{\mathrm{eff}}\ensuremath{\simeq}0.6{7}_{\ensuremath{-}0.48}^{+0.26}\text{ }\text{ }\mathrm{eV}$ with a contribution to $\mathrm{\ensuremath{\Delta}}{N}_{\mathrm{eff}}\ensuremath{\simeq}0.06\ifmmode\pm\else\textpm\fi{}0.05$. However, Pantheon and BOSS $\mathrm{BAO}/f{\ensuremath{\sigma}}_{8}$ data restricts the particle mass to ${m}_{\mathrm{sp}}^{\mathrm{eff}}\ensuremath{\simeq}0.4{8}_{\ensuremath{-}0.36}^{+0.17}$ and contribution to $\mathrm{\ensuremath{\Delta}}{N}_{\mathrm{eff}}\ensuremath{\simeq}0.04{6}_{\ensuremath{-}0.031}^{+0.004}$. We discuss implications of our results for other canonical nonthermal HDM models---the Dodelson-Widrow model and a hidden sector model of a thermal sterile particle with a different temperature. We report competitive results on such hidden sector temperature that might have interesting implications for particle physics model building, in particular connecting the ${S}_{8}$ tension to the longstanding short baseline oscillation anomaly.

Kinematic Decomposition of the H i Gaseous Component in the Large Magellanic Cloud

Abstract We perform a profile analysis of the combined H i data cube of the Large Magellanic Cloud (LMC) from observations with the Australia Telescope Compact Array and the Parkes radio telescope. For the profile analysis, we use a newly developed algorithm that decomposes individual line profiles into an optimal number of Gaussian components based on a Bayesian nested sampling. The decomposed Gaussian components are then classified into kinematically cold, warm, and hot gas components based on their velocity dispersion. The estimated masses of the kinematically cold, warm, and hot gas components are ∼12.2%, ∼58.3%, and ∼29.5% of the total H i mass of the LMC, respectively. Our analysis reveals the highly complex H i structure and kinematics of the LMC that are seen in previous studies but in a more quantitative manner. We also extract the undisturbed H i gas bulk motions and derive new H i gas bulk rotation curves of the LMC by applying a 2D tilted-ring analysis. In contrast to previously derived H i rotation curves, the newly derived bulk rotation curves are much more consistent with the carbon star kinematics, with rotation velocity linearly increasing in the inner part and reaching a maximum of ∼60 km s−1 at the outermost measured radius. By comparing the lower bulk rotation curves with previous studies, we conclude that there is a lower dynamical contribution of dark matter in the central part of the LMC.

Dark matter from torsion in Friedmann cosmology

A cosmological model in an Einstein–Cartan framework endowed with torsion is studied. For a torsion function assumed to be proportional to Hubble expansion function, namely phi =-alpha H, the contribution of torsion function as a dark matter component is studied in two different approaches. In the first one, the total matter energy density is altered by torsion coupling alpha , giving rise to an effective dark matter and cosmological constant terms that reproduce quite well the flat cosmic concordance model. In the second approach, starting with just standard baryonic matter plus a cosmological constant term, it is obtained that the coupling of torsion with baryons and cosmological constant term naturally gives rise to a dark matter contribution, together a modified cosmological term. In this model the dark matter sector can be interpreted as an effective coupling of the torsion function with the ordinary baryonic matter and cosmological constant. Finally, it is shown that both models are totally compatible with recent cosmological data from Supernovae and Hubble parameter measurements.

Widened R&amp;lt;sup&amp;gt;&amp;lt;i&amp;gt;n&amp;lt;/i&amp;gt;&amp;lt;/sup&amp;gt; General Relativity

An extension of General Relativity is presented based on a scalar Lagrangian density which is a general function of all the independent invariant scalars that one is able to build by the powers of the Ricci tensor. It is shown how the new terms arising in the generalized Einstein filed equations may be interpreted as dark matter and dark energy contributions. Metricity condition fulfilled by a new tensor different than the usual metric tensor is also obtained. Moreover, it is shown that Schwarzschild-De Sitter, Robertson-Walker-De Sitter and Kerr-De Sitter metrics are exact solutions to the new field equations. Remarkably, the form of the equation of the geodesic trajectories of particle motions across space-time remains the same as in Einstein General Relativity unless the cosmological constant Lambda is no longer a constant becoming a function of the space-time co-ordinates.

Dynamics and epicyclic motions of particles around the Schwarzschild\u2013de Sitter black hole in perfect fluid dark matter

In this paper, we investigate circular orbits for test particles around the Schwarzschild–de Sitter (dS) black hole surrounded by perfect fluid dark matter. We determine the region of circular orbits bounded by innermost and outermost stable circular orbits. We show that the impact of the perfect fluid dark matter shrinks the region where circular orbits can exist as the values of both innermost and outermost stable circular orbits decrease. We find that for specific lower and upper values of the dark matter parameter there exist double matching values for inner and outermost stable circular orbits. It turns out that the gravitational attraction due to the dark matter contribution dominates over cosmological repulsion. This gives rise to a remarkable result in the Schwarzschild–de Sitter black hole surrounded by dark matter field in contrast to the Schwarzschild–de Sitter metric. Finally, we study epicyclic motion and its frequencies with their applications to twin peak quasi-periodic oscillations (QPOs) for various models. We find the corresponding values of the black hole parameters which could best fit and explain the observed twin peak QPO object GRS 1915+109 from microquasars.

Black holes and WIMPs: all or nothing or something else

ABSTRACT We consider constraints on primordial black holes (PBHs) in the mass range $(10^{-18}\!-\!10^{15})\, \mathrm{M}_{\odot }$ if the dark matter (DM) comprises weakly interacting massive particles (WIMPs) that form haloes around them and generate γ-rays by annihilations. We first study the formation of the haloes and find that their density profile prior to WIMP annihilations evolves to a characteristic power-law form. Because of the wide range of PBH masses considered, our analysis forges an interesting link between previous approaches to this problem. We then consider the effect of the WIMP annihilations on the halo profile and the associated generation of γ-rays. The observed extragalactic γ-ray background implies that the PBH DM fraction is $f^{}_{\rm PBH} \lesssim 2 \times 10^{-9}\, (m_{\chi } / {\rm TeV})^{1.1}$ in the mass range $2 \times 10^{-12}\, \mathrm{M}_{\odot }\, (m_{\chi } / {\rm TeV})^{-3.2} \lesssim M \lesssim 5 \times 10^{12}\, \mathrm{M}_{\odot }\, (m_{\chi } / {\rm TeV})^{1.1}$, where mχ and M are the WIMP and PBH masses, respectively. This limit is independent of M and therefore applies for any PBH mass function. For $M \lesssim 2\times 10^{-12}\, \mathrm{M}_{\odot }\, (m_{\chi }/ {\rm TeV})^{-3.2}$, the constraint on $f^{}_{\rm PBH}$ is a decreasing function of M and PBHs could still make a significant DM contribution at very low masses. We also consider constraints on WIMPs if the DM is mostly PBHs. If the merging black holes recently discovered by LIGO/Virgo are of primordial origin, this would rule out the standard WIMP DM scenario. More generally, the WIMP DM fraction cannot exceed 10−4 for $M \gt 10^{-9}\, \mathrm{M}_{\odot }$ and $m_{\chi } \gt 10\,$ GeV. There is a region of parameter space, with $M \lesssim 10^{-11}\, \mathrm{M}_{\odot }$ and $m_{\chi } \lesssim 100\,$ GeV, in which WIMPs and PBHs can both provide some but not all of the DM, so that one requires a third DM candidate.

Search for Gravitational Waves from the Coalescence of Subsolar Mass and Eccentric Compact Binaries

Abstract We present a search for gravitational waves from subsolar mass compact-binary mergers that allows for nonnegligible orbital eccentricity. Subsolar mass black holes are a signature of primordial origin black holes, which may be a component of dark matter. To produce binary coalescences, primordial black holes may form close binaries either in the early universe or more recently through dynamical interactions. A signature of dynamical formation would be the observation of noncircularized orbits. We search for black hole mergers where the primary mass is 0.1–7M ⊙ and the secondary mass is 0.1–1M ⊙. We allow for eccentricity up to ∼0.3 at a dominant-mode gravitational-wave frequency of 10 Hz for binaries with component masses &gt;0.5M ⊙. We find no convincing candidates in the public LIGO data from 2015–2017. The two most promising candidates have a false alarm rate of 1 per 3 and 4 yr, respectively, which combined is only a ∼2.4σ deviation from the expected Poisson rate. Given the marginal statistical significance, we place upper limits on the rate of subsolar mass mergers under the assumption of a null observation and compare how these limits may inform the possible dark matter contribution.

Testing the weak cosmic censorship conjecture for a Reissner\u2013Nordstr\xf6m\u2013de Sitter black hole surrounded by perfect fluid dark matter

In this paper, we test the weak cosmic censorship conjecture (WCCC) for the Reissner–Nordström–de Sitter (RN-dS) black hole surrounded by perfect fluid dark matter. We consider a spherically symmetric perturbation on deriving linear and non-linear order perturbation inequalities by applying a new version of gedanken experiments well accepted from the work of Sorce and Wald. Contrary to the well-known result that the Reissner–Nordström (RN) black hole could be overcharged under linear order particle accretion it is hereby shown that the same black hole in perfect fluid dark matter with cosmological parameter cannot be overcharged. Considering a realistic scenario in which black holes cannot be considered to be in vacuum we investigate the contribution of dark matter and cosmological constant in the overcharging process of an electrically charged black hole. We demonstrate that the black hole can be overcharged only when two fields induced by dark matter and cosmological parameter are completely balanced. Further we present a remarkable result that a black hole cannot be overcharged beyond a certain threshold limit for which the effect arising from the cosmological constant dominates over the effect by the perfect fluid dark matter. Thus even for a linear accretion process, the black hole cannot always be overcharged and hence obeys the WCCC in general. This result would continue to be fulfilled for non-linear order accretion.

Scaling Behavior for the Susceptibility of the Vacuum

Using the two-component superfluid model of Winterberg for space, two models for the susceptibility of the cosmic vacuum as a function of the cosmic scale parameter, a, are presented. We also consider the possibility that Newton’s constant can scale, i.e., G-1=G-1(a), to form the most general scaling laws for polarization of the vacuum. The positive and negative values for the Planckion mass, which form the basis of the Winterberg model, are inextricably linked to the value of G, and as such, both G and Planck mass are intrinsic properties of the vacuum. Scaling laws for the non-local, smeared, cosmic susceptibility, , the cosmic polarization, , the cosmic macroscopic gravitational field, , and the cosmic gravitational field mass density, , are worked out, with specific examples. At the end of recombination, i.e., the era of last scattering, using the polarization to explain dark matter, and the gravitational field mass density to explain dark energy, we find that, . While this is an unconventional assignment, differing from the ΛCDM model, we believe this is correct, as localized dark matter (LDM) contributions can be much higher in this epoch than cosmic smeared values for susceptibility. All density parameter assignments in Friedmanns’ equation are cosmic averages, valid for distance scales in excess of 100 Mpc in the current epoch. We also evaluate the transition from ordinary matter dominance, to dark matter dominance, for the cosmos as a whole. We obtain for the transition points, z=1.66, for susceptibility model I, and, z=2.53 , for susceptibility model II.

Dynamical masses of brightest cluster galaxies – II. Constraints on the stellar IMF

ABSTRACT We use stellar and dynamical mass profiles, combined with a stellar population analysis, of 32 brightest cluster galaxies (BCGs) at redshifts of 0.05 ≤$z$ ≤ 0.30, to place constraints on their stellar initial mass function (IMF). We measure the spatially resolved stellar population properties of the BCGs, and use it to derive their stellar mass-to-light ratios ($\Upsilon _{\star \rm POP}$). We find young stellar populations (&amp;lt;200 Myr) in the centres of 22 per cent of the sample, and constant $\Upsilon _{\star \rm POP}$ within 15 kpc for 60 per cent of the sample. We further use the stellar mass-to-light ratio from the dynamical mass profiles of the BCGs ($\Upsilon _{\star \rm DYN}$), modelled using a multi-Gaussian expansion and Jeans Anisotropic Method, with the dark matter contribution explicitly constrained from weak gravitational lensing measurements. We directly compare the stellar mass-to-light ratios derived from the two independent methods, $\Upsilon _{\star \rm POP}$ (assuming some IMF) to $\Upsilon _{\star \rm DYN}$ for the subsample of BCGs with no young stellar populations and constant $\Upsilon _{\star \rm POP}$. We find that for the majority of these BCGs, a Salpeter (or even more bottom-heavy) IMF is needed to reconcile the stellar population and dynamical modelling results although for a small number of BCGs, a Kroupa (or even lighter) IMF is preferred. For those BCGs better fit with a Salpeter IMF, we find that the mass-excess factor against velocity dispersion falls on an extrapolation (towards higher masses) of known literature correlations. We conclude that there is substantial scatter in the IMF amongst the highest mass galaxies.