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Antonino Del Popolo

Publications and source records attributed to Antonino Del Popolo.

At least 55 records · Page 3Linked to original sources
arXiv2019

Correlations in the matter distribution in CLASH galaxy clusters

We study the total and dark matter (DM) density profiles as well as their correlations for a sample of 15 high-mass galaxy clusters by extending our previous work on several clusters from Newman et al. Our analysis focuses on 15 CLASH X-ray-selected clusters that have high-quality weak- and strong-lensing measurements from combined Subaru and {\em Hubble Space Telescope} observations. The total density profiles derived from lensing are interpreted based on the two-phase scenario of cluster formation. In this context, the brightest cluster galaxy (BCG) forms in the first dissipative phase, followed by a dissipationless phase where baryonic physics flattens the inner DM distribution. This results in the formation of clusters with modified DM distribution and several correlations between characteristic quantities of the clusters. We find that the central DM density profiles of the clusters are strongly influenced by baryonic physics as found in our earlier work. The inner slope of the DM density for the CLASH clusters is found to be flatter than the Navarro--Frenk--White profile, ranging from $α=0.30$ to $0.79$. We examine correlations of the DM density slope $α$ with the effective radius $R_\mathrm{e}$ and stellar mass $M_\mathrm{e}$ of the BCG, finding that these quantities are anti-correlated with a Spearman correlation coefficient of $\sim -0.6$. We also study the correlation between $R_\mathrm{e}$ and the cluster halo mass $M_{500}$, and the correlation between the total masses inside 5\,kpc and 100\,kpc. We find that these quantities are correlated with Spearman coefficients of $0.68$ and $0.64$, respectively. These observed correlations are in support of the physical picture proposed by Newman et al.

astro-ph.CO↗
arXiv2019

Dark compact objects: an extensive overview

We study the structure of compact objects that contain non-self annihilating, self-interacting dark matter admixed with ordinary matter made of neutron star and white dwarf materials. We extend the previous work Phys. Rev. D 92 123002 (2015) on these dark compact objects by analyzing the effect of weak and strongly interacting dark matter with particle masses in the range of 1-500 GeV, so as to set some constraints in the strength of the interaction and the mass of the dark matter particle. We find that the total mass of the compact objects increases with decreasing dark matter particle mass. In the strong interacting case and for dark matter particle masses in the range 1-10 GeV, the total mass of the compact objects largely exceeds the $2M_\odot$ constraint for neutron star masses and the nominal $1M_\odot$for white dwarfs, while for larger dark matter particle masses or in the weakly interacting case the compact objects show masses in agreement or smaller than these constraints, thus hinting at the exclusion of strongly self-interacting dark matter of masses 1-10 GeV in the interior of these compact objects. Moreover, we observe that the smaller the dark matter particle mass, the larger the quantity of dark matter captured is, putting constraints on the dark matter mass trapped in the compact objects so as to fullfill $\simeq 2M_\odot$ observations. Finally, the inhomogeneity of distribution of dark matter in the Galaxy implies a mass dependence of compact objects from the environment which can be used to put constraints on the characteristics of the Galaxy halo DM profile and on particle mass. In view of the these results, we discuss the formation of the dark compact objects in an homogeneous and non-homogeneous dark matter environment.

gr-qc↗
arXiv2018

Energy transfer from baryons to dark matter as a unified solution to small-scale structure issues of the $Λ$CDM model

Using a semianalytic code, we show how baryon physics in a $Λ$CDM cosmology could solve the discrepancy between numerical predictions of dark matter haloes and observations, ranging from dwarf galaxies to clusters, without the need of nonstandard dark matter models as advocated, for example, by [Kaplinghat et al., Phys. Rev. Lett. 116, 041302, (2016)]. Combining well established results, we show, for the first time, how accounting for baryon physics, in particular dynamical friction mechanisms, leads to flat galaxy-cluster profiles and correlations in several of their properties, solves the so-called `diversity problem' and reproduces very well the challenging, extremely low-rising rotation curve of IC2574. We therefore suggest treating baryonic physics properly before introducing new exotic features, albeit legitimate, in the standard cosmological model.

astro-ph.GA↗
arXiv2018

Mass functions from the excursion set model

Aims. We aim to study the stochastic evolution of the smoothed overdensity $δ$ at scale $S$ of the form $δ(S) = \int_{0}^S K(S,u)\mathrm{d}W(u)$, where $K$ is a kernel and $\mathrm{d}W$ is the usual Wiener process. Methods. For a Gaussian density field, smoothed by the top-hat filter, in real space, we used a simple kernel that gives the correct correlation between scales. A Monte Carlo procedure was used to construct random walks and to calculate first crossing distributions and consequently mass functions for a constant barrier. Results. We show that the evolution considered here improves the agreement with the results of N-body simulations relative to analytical approximations which have been proposed from the same problem by other authors. In fact, we show that an evolution which is fully consistent with the ideas of the excursion set model, describes accurately the mass function of dark matter haloes for values of $ν\leq 1$ and underestimates the number of larger haloes. Finally, we show that a constant threshold of collapse, lower than it is usually used, it is able to produce a mass function which approximates the results of N-body simulations for a variety of redshifts and for a wide range of masses. Conclusions. A mass function in good agreement with N-body simulations can be obtained analytically using a lower than usual constant collapse threshold.

astro-ph.CO↗
arXiv2017

Quantifying Departures from Equilibrium with the Spherical Jeans Equation

Proper motions of collisionless pointlike objects in a spherically symmetric system, for example stars in a galaxy, can be used to test whether that system is in equilibrium, with no assumptions regarding isotropy. In particular, the fourth order spherical Jeans equation yields expressions for two observable quantities characterizing the departure from equilibrium, both of which can be expressed in terms of time derivatives of first and third moments of the velocities. As illustrations, we compute these quantities for tracer distributions drawn from an exact equilibrium configuration and also from near equilibrium configurations generated using the N-body code GALIC.

astro-ph.GA↗
arXiv2017

Small scale problems of the $Λ$CDM model: a short review

The $Λ$CDM model, or concordance cosmology, as it is often called, is a paradigm at its maturity. It is clearly able to describe the universe at large scale, even if some issues remain open, such as the cosmological constant problem , the small-scale problems in galaxy formation, or the unexplained anomalies in the CMB. $Λ$CDM clearly shows difficulty at small scales, which could be related to our scant understanding, from the nature of dark matter to that of gravity; or to the role of baryon physics, which is not well understood and implemented in simulation codes or in semi-analytic models. At this stage, it is of fundamental importance to understand whether the problems encountered by the $Λ$DCM model are a sign of its limits or a sign of our failures in getting the finer details right. In the present paper, we will review the small-scale problems of the $Λ$CDM model, and we will discuss the proposed solutions and to what extent they are able to give us a theory accurately describing the phenomena in the complete range of scale of the observed universe.

astro-ph.CO↗
arXiv2017

A high precision semi-analytic mass function

In this paper, extending past works of Del Popolo, we show how a high precision mass function (MF) can be obtained using the excursion set approach and an improved barrier taking implicitly into account a non-zero cosmological constant, the angular momentum acquired by tidal interaction of proto-structures and dynamical friction. In the case of the $Λ$CDM paradigm, we find that our MF is in agreement at the 3\% level to Klypin's Bolshoi simulation, in the mass range $M_{\rm vir} = 5 \times 10^9 h^{-1} M_{\odot} -- 5 \times 10^{14} h^{-1} M_{\odot}$ and redshift range $0 \lesssim z \lesssim 10$. For $z=0$ we also compared our MF to several fitting formulae, and found in particular agreement with Bhattacharya's within 3\% in the mass range $10^{12}-10^{16} h^{-1} M_{\odot}$. Moreover, we discuss our MF validity for different cosmologies.

astro-ph.CO↗
arXiv2017

On the first crossing distributions in fractional Brownian motion and the mass function of dark matter haloes

We construct an integral equation for the first crossing distributions for fractional Brownian motion in the case of a constant barrier and we present an exact analytical solution. Additionally we present first crossing distributions derived by simulating paths from fractional Brownian motion. We compare the results of the analytical solutions with both those of simulations and those of some approximated solutions which have been used in the literature. Finally, we present multiplicity functions for dark matter structures resulting from our analytical approach and we compare with those resulting from N-body simulations. We show that the results of analytical solutions are in good agreement with those of path simulations but differ significantly from those derived from approximated solutions. Additionally, multiplicity functions derived from fractional Brownian motion are poor fits of the those which result from N-body simulations. We also present comparisons with other models which exist in the literature and we discuss different ways of improving the agreement between analytical results and N-body simulations.

astro-ph.CO↗
arXiv2016

Constraints on shear and rotation with massive galaxy clusters

A precise determination of the mass function is an important tool to verify cosmological predictions of the $Λ$CDM model and to infer more precisely the better model describing the evolution of the Universe. Galaxy clusters have been currently used to infer cosmological parameters, in particular the matter density parameter $Ω_{\rm m}$, the matter power spectrum normalization $σ_8$ and the equation of state parameter $w_{\rm de}$ of the dark energy fluid. In this work, using data on massive galaxy clusters ($M>8\times 10^{14}~h^{-1}~M_{\odot}$) in the redshift range $0.05\lesssim z\lesssim 0.83$ we put constraints on the parameter $α$ introduced within the formalism of the extended spherical collapse model to quantify deviations from sphericity due to shear and rotation. Since at the moment there is no physical model describing its functional shape, we assume it to be a logarithmic function of the cluster mass. By holding $σ_8$ fixed and restricting our analysis to a $Λ$CDM model, we find, at $1-σ$ confidence level, $Ω_{\rm m}=0.284\pm0.0064$, $h=0.678\pm0.017$ and $β=0.0019^{+0.0008}_{-0.0015}$, where $β$ represents the slope of the parameter $α$. This results translates into a $9\%$ decrement of the number of massive clusters with respect to a standard $Λ$CDM mass function, but better data are required to better constrain this quantity, since at the $2-σ$ and $3-σ$ confidence level we are only able to infer upper limits.

astro-ph.CO↗
arXiv2014

A unified solution to the small scale problems of the $Λ$CDM model II: introducing parent-satellite interaction

We continue the study of the impact of baryon physics on the small scale problems of the $Λ$CDM model, based on a semi-analytical model (Del Popolo, 2009). Withsuch model, we show how the cusp/core, missing satellite (MSP), Too Big to Fail (TBTF) problems and the angular momentum catastrophe can be reconciled with observations, adding parent-satellite interaction. Such interaction between darkmatter (DM) and baryons through dynamical friction (DF) can sufficiently flattenthe inner cusp of the density profiles to solve the cusp/core problem. Combining, in our model, a Zolotov et al. (2012)-like correction, similarly to Brooks et al. (2013), and effects of UV heating and tidal stripping, the number of massive, luminous satellites, as seen in the Via Lactea 2 (VL2) subhaloes,is in agreement with the numbers observed in the MW, thus resolving the MSP and TBTF problems. The model also produces a distribution of the angular spin parameter and angular momentum in agreement with observations of the dwarfs studied by van den Bosch, Burkert, \\& Swaters (2001).

astro-ph.CO↗
arXiv2014

Cusps and Cores in the presence of galactic bulges

In this paper, we study how the presence of bulge formation in galaxies influence their inner density profile, by means of an extended version of the Del Popolo (2009) semi-analytical model. As in Del Popolo (2009), the model takes into account the effect of baryons adiabatic contraction, ordered and random angular momentum, dynamical friction, and adds to the previous the effect of gas cooling, star formation, supernova feedback, and reionization. Our model shows that dwarf galaxies are bulgeless, in agreement with observations showing that the large majority of them has no stellar bulges, and are characterized by a flat profile well described by a Burkert profile. {We then studied the effect of a bulge, added to the {cored} DM halo, on the density profile}. In the case of a galaxy having a mass $10^{11} M_{\odot}$ the inner density profile has a slope $α\simeq 0.65$, for a bulge of $4.5 \times 10^{9} M_{\odot}$, while if bulge formation is not considered, the slope would be $α\simeq 0.55$. If the bulge is larger, $6.5 \times 10^{9} M_{\odot}$ the slope is $α\simeq 0.7$. In the case of a larger galaxy with $10^{12} M_{\odot}$ the slope is $α\simeq 0.85$, while in absence of bulge it is $α\simeq 0.75$. We finally study how the inner slope $α$ changes with the bulge mass, and we find a correlation among the two quantities. The result shows that bulge formation has an important role in shaping the inner DM density profile in agreement with Inoue & Saitoh (2011) result. The result implies that going from Sc to SO Hubble type the slope is slightly steepening due to the bulge formation, and due to the fact that early type galaxies have larger bulges.

astro-ph.GA↗
arXiv2013

A fully quantum model of Big Bang

In the paper the closed Friedmann-Robertson-Walker model with quantization in the presence of the positive cosmological constant and radiation is studied. For analysis of tunneling probability for birth of an asymptotically deSitter, inflationary Universe as a function of the radiation energy a new definition of a "free" wave propagating inside strong fields is proposed. On such a basis, tunneling boundary condition is corrected, penetrability and reflection concerning to the barrier are calculated in fully quantum stationary approach. For the first time non-zero interference between the incident and reflected waves has been taken into account which turns out to play important role inside cosmological potentials and could be explained by non-locality of barriers in quantum mechanics. Inside whole region of energy of radiation the tunneling probability for the birth of the inflationary Universe is found to be close to its value obtained in semiclassical approach. The reflection from the barrier is determined for the first time (which is essentially differs on 1 at the energy of radiation close to the barrier height). The proposed method could be easily generalized on the cosmological models with the barriers of arbitrary shape, that has been demonstrated for the FRW-model with included Chaplygin gas. Result is stable for variations of the studied barriers, accuracy are found to be 11--18 digits for all coefficients and energies below the barrier height.

gr-qc↗
arXiv2012

Extended Spherical Collapse and the Accelerating Universe

The influence of the shear stress and angular momentum on the nonlinear spherical collapse model is discussed in the framework of the Einstein-de Sitter (EdS) and $Λ$CDM models. By assuming that the vacuum component is not clustering within the homogeneous nonspherical overdensities, we show how the local rotation and shear affects the linear density threshold for collapse of the non-relativistic component ($δ_\mathrm{c}$) and its virial overdensity ($Δ_\mathrm{V}$). It is also found that the net effect of shear and rotation in galactic scale is responsible for higher values of the linear overdensity parameter as compared with the standard spherical collapse model (no shear and rotation).

astro-ph.CO↗
arXiv2012

Cosmological measure with volume averaging and the vacuum energy problem

In this paper, we give a possible solution to the cosmological constant problem. It is shown hat the traditional approach, based on volume weighting of probabilities, leads to an incoherent onclusion: the probability that a randomly chosen observer measures $Λ=0$ is exactly equal to 1. Using an alternative, volume averaging measure, instead of volume weighting can explain why the osmological constant is non-zero.

gr-qc↗
arXiv2009

How initial and boundary conditions affect protoplanetary migration in a turbulent sub-Keplerian accretion disc: 2D non viscous SPH simulations

Current theories on planetary formation establish that giant planet formation should be contextual to their quick migration towards the central star due to the protoplanets-disc interactions on a timescale of the order of $10^5$ years, for objects of nearly 10 terrestrial masses. Such a timescale should be smaller by an order of magnitude than that of gas accretion onto the protoplanet during the hierarchical growing-up of protoplanets by collisions with other minor objects. These arguments have recently been analysed using N-body and/or fluid-dynamics codes or a mixing of them. In this work, inviscid 2D simulations are performed, using the SPH method, to study the migration of one protoplanet, to evaluate the effectiveness of the accretion disc in the protoplanet dragging towards the central star, as a function of the mass of the planet itself, of disc tangential kinematics. To this purpose, the SPH scheme is considered suitable to study the roles of turbulence, kinematic and boundary conditions, due to its intrinsic advective turbulence, especially in 2D and in 3D codes. Simulations are performed both in disc sub-Keplerian and in Keplerian kinematic conditions as a parameter study of protoplanetary migration if moderate and consistent deviations from Keplerian Kinematics occur. Our results show migration times of a few orbital periods for Earth-like planets in sub-Keplerian conditions, while for Jupiter-like planets estimates give that about $10^4$ orbital periods are needed to half the orbital size. Timescales of planet migration are strongly dependent on the relative position of the planet with respect to the shock region near the centrifugal barrier of the disc flow.

astro-ph.EP↗
arXiv2009

An Abs Algorithm for a Class of Systems of Stochastic Linear Equations

This paper is to explore a model of the ABS Algorithms dealing with the solution of a class of systems of linear stochastic equations $Aξ=η$ when $η$ is a $m$-dimensional normal distribution. It is shown that the stepsize $α_i$ is distributed as $N(u_i,σ_i)$ (being $u_i$ the expected value of $α_i$ and $σ_i$ its variance) and the approximation to the solutions $ξ_{i}$ is distributed as $N_n(U_i,Σ_i)$ (being $U_i$ the expected value of $ξ_i$ and $Σ_i$ its variance), for this algorithm model.

astro-ph.IM↗
arXiv2008

Some improvements to the spherical collapse model

I study the joint effect of dynamical friction, tidal torques and cosmological constant on clusters of galaxies formation I show that within high-density environments, such as rich clusters of galaxies, both dynamical friction and tidal torques slows down the collapse of low-? peaks producing an observable variation in the time of collapse of the perturbation and, as a consequence, a reduction in the mass bound to the collapsed perturbation Moreover, the delay of the collapse produces a tendency for less dense regions to accrete less mass, with respect to a classical spherical model, inducing a biasing of over-dense regions toward higher mass I show how the threshold of collapse is modified if dynamical friction, tidal torques and a non-zero cosmological constant are taken into account and I use the Extended Press Schecter (EPS) approach to calculate the effects on the mass function Then, I compare the numerical mass function given in Reed et al (2003) with the theoretical mass function obtained in the present paper I show that the barrier obtained in the present paper gives rise to a better description of the mass function evolution with respect to other previous models (Sheth & Tormen 1999, MNRAS, 308, 119 (hereafter ST); Sheth & Tormen 2002, MNRAS, 329, 61 (hereafter ST1))

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