arXiv subjects

A. Del Popolo

Publications and source records attributed to A. Del Popolo.

At least 91 records · Page 5Linked to original sources

arXiv2012

Surface Density of dark matter haloes on galactic and cluster scales

In this paper, in the framework of the secondary infall model, the correlation between the central surface density and the halo core radius of galaxy, and cluster of galaxies, dark matter haloes was analyzed, this having recently been studied on a wide range of scales. We used Del Popolo (2009) secondary infall model taking into account ordered and random angular momentum, dynamical friction, and dark matter (DM) adiabatic contraction to calculate the density profile of haloes, and then these profiles are used to determine the surface density of DM haloes. The main result is that $r_\ast$ (the halo characteristic radius) is not an universal quantity as claimed by Donato et al. (2009) and Gentile et al. (2009). On the contrary, we find a correlation with the halo mass $M_{200}$ in agreement with Cardone & Tortora (2010), Boyarsky at al. (2009) and Napolitano et al. (2010), but with a significantly smaller scatter, namely $0.16 \pm 0.05$. We also consider the baryon column density finding this latter being indeed a constant for low mass systems such as dwarfs, but correlating with mass with a slope $α= 0.18 \pm 0.05$. In the case of the surface density of dark matter for a system composed only of dark matter, as in dissipationless simulations, we get $α=0.20 \pm 0.05$. These results leave little room for the recently claimed universality of (dark and stellar) column density.

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arXiv2012

Spherical collapse model with shear and angular momentum in dark energy cosmologies

We study, for the first time, how shear and angular momentum modify typical parameters of the spherical collapse model, in dark energy dominated universes. In particular, we study the linear density threshold for collapse $δ_\mathrm{c}$ and the virial overdensity $Δ_\mathrm{V}$, for several dark-energy models and its influence on the cumulative mass function. The equations of the spherical collapse are those obtained in Pace et al. (2010), who used the fully nonlinear differential equation for the evolution of the density contrast derived from Newtonian hydrodynamics, and assumed that dark energy is present only at the background level. With the introduction of the shear and rotation terms, the parameters of the spherical collapse model are now mass-dependant. The results of the paper show, as expected, that the new terms considered in the spherical collapse model oppose the collapse of perturbations on galactic scale giving rise to higher values of the linear overdensity parameter with respect to the non-rotating case. We find a similar effect also for the virial overdensity parameter. For what concerns the mass function, we find that its high mass tail is suppressed, while the low mass tail is slightly affected except in some cases, e.g. the Chaplygin gas case.

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arXiv2012

The Dark Matter Haloes of Chandra X-ray Galaxy Clusters and Baryons Effect

We present results based on Chandra observations of a large sample of 129 hot galaxy clusters. We measure the concentration parameter c_200, the dark mass M_200 and the baryonic mass content in all the objects of our sample, providing the largest dataset of mass parameters for galaxy clusters in the redshift range z = 0.01 - 1.4. We confirm a that a tight correlation between c_200 and M_200, c \propto M^a_vir /(1+z)^b with a = -0.56 +/- 0.15 and b =0.80 +/- 0.25 (68 per cent confidence limits), is present, in good agreement with the predictions from numerical simulations and previous observations. Fitting the mass profile with a generalized NFW model, we got the inner slope alpha, with alpha = 0.94 +/- 0.13. Finally, we show that the inner slope of the density profile, alpha correlates with the baryonic mass content, M_b : namely alpha is decreasing with increasing baryonic mass content.

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arXiv2012

Newtonian acceleration scales in spiral galaxies

We revisit the issue of the constancy of the dark matter (DM) and baryonic Newtonian acceleration scales within the DM scale radius by considering a large sample of late - type galaxies. We rely on a Markov Chain Monte Carlo (MCMC) method to estimate the parameters of the halo model and the stellar mass - to - light ratio and then propagate the uncertainties from the rotation curve data to the estimate of the acceleration scales. This procedure allows us to compile a catalog of 58 objects with estimated values of the $B$ band absolute magnitude $M_B$, the virial mass $M_{vir}$, the DM and baryonic Newtonian accelerations (denoted as $g_{DM}(r_0)$ and $g_{bar}(r_0)$, respectively) within the scale radius $r_0$ which we use to investigate whether it is possible to define a universal acceleration scale. We find a weak but statistically meaningful correlation with $M_{vir}$ thus making us argue against the universality of the acceleration scales. However, the results somewhat depend on the sample adopted so that a careful analysis of selection effects should be carried out before any definitive conclusion can be drawn.

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arXiv2012

On the Density profile slope of Clusters of Galaxies

The present paper extends to clusters of galaxies the study of Del Popolo (2012), concerning how the baryon-dark matter (DM) interplay shapes the density profile of dwarf galaxies. Cluster density profiles are determined taking into account dynamical friction, random and ordered angular momentum and the response of dark matter halos to condensation of baryons. We find that halos containing only DM are characterized by Einasto's profiles, and that the profile flattens with increasing content of baryons, and increasing values of random angular momentum. The analytical results obtained in the first part of the paper were applied to well studied clusters whose inner profiles have slopes flatter than NFW predictions (A611, A383) or are characterized by profiles in agreement with the NFW model (MACS J1423.8+2404, RXJ1133). By using independently-measured baryonic fraction, a typical spin parameter value $λ\simeq 0.03$, and adjusting the random angular momentum, we re-obtain the mass and density profiles of the quoted clusters. Finally, we show that the baryonic mass inside $\simeq 10$ kpc, $M_{b,in}$ is correlated with the total mass of the clusters, %finding a correlation among the two quantities, as $M_{b,in} \propto M_{500}^{0.4}$.

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arXiv2012

Statistical properties of the dark matter haloes of dwarf galaxies and correlations with the environment

According to the now strongly supported concordance $Λ$CDM model, galaxies may be grossly described as a luminous component embedded in a dark matter halo. The density profile of these mass dominating haloes may be determined by N - body simulations which mimic the evolution of the tiny initial density perturbations during the process leading to the structures we observe today. Unfortunately, when the effect of baryons is taken into account, the situation gets much more complicated due to the difficulties in simulating their physics. As a consequence, a definitive prediction of how dark matter haloes should presently look like is still missing. We revisit here this issue from an observational point of view devoting our attention to dwarf galaxies. Being likely dark matter dominated, these systems are ideal candidates to investigate the present day halo density profiles and check whether dark matter related quantities correlate with the stellar ones or the environment. By fitting a large sample of well measured rotation curves, we infer constraints on both halo structural parameters (such as the logarithmic slope of the density profile and its concentration) and derived quantities (e.g., the mass fraction and the Newtonian acceleration) which could then be used to constrain galaxy formation scenarios. Moreover, we investigate whether the halo properties correlates with the environment the galaxy lives in thus offering a new tool to deepen our understanding of galaxy formation.

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arXiv2011

Non--power law behavior of the radial profile of phase--space density of halos

We study the pseudo phase-space density, $ρ(r)/σ^3(r)$, of $Λ$CDM dark matter halos with and without baryons (baryons+DM, and pure DM), by using the model introduced in Del Popolo (2009), which takes into account the effect of dynamical friction, ordered and random angular momentum, baryons adiabatic contraction and dark matter baryons interplay. We examine the radial dependence of $ρ(r)/σ^3(r)$ over 9 orders of magnitude in radius for structures on galactic and cluster of galaxies scales. We find that $ρ(r)/σ^3(r)$ is approximately a power-law only in the range of halo radius resolved by current simulations (down to 0.1% of the virial radius) while it has a non-power law behavior below the quoted scale, with inner profiles changing with mass. The non-power-law behavior is more evident for halos constituted both of dark matter and baryons while halos constituted just of dark matter and with angular momentum chosen to reproduce a Navarro-Frenk-White (NFW) density profile, are characterized by an approximately power-law behavior. The results of the present paper lead to conclude that density profiles of the NFW type are compatible with a power-law behavior of $ρ(r)/σ^3(r)$, while those flattening to the halo center, like those found in Del Popolo (2009) or the Einasto profile, or the Burkert profile, cannot produce radial profile of the pseudo-phase-space density that are power-laws at all radii. The results argue against universality of the pseudo phase-space density and as a consequence argue against universality of density profiles constituted by dark matter and baryons as also discussed in Del Popolo (2009).

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arXiv2011

Density profile slope in Dwarfs and environment

In the present paper, we study how the dark matter density profiles of dwarfs galaxies in the mass range $10^8-10^{10} M_{\odot}$ are modified by the interaction of the dwarf in study with the neighboring structures, and by changing baryon fraction in dwarfs. As already shown in Del Popolo (2009), the slope of density profile of inner halos flattens with decreasing halo mass and the profile is well approximated by a Burkert's profile. The analysis shows that dwarfs who suffered a smaller tidal torquing (consequently having smaller angular momentum) are characterized by steeper profiles with respect to dwarfs subject to higher torque, and similarly dwarfs having a smaller baryons fraction have also steeper profiles than those having a larger baryon fraction. In the case tidal torquing is shut down and baryons are not present, the density profile is very well approximated by an Einasto profile, similarly to dwarfs obtained in dissipationless N-body simulations. We then apply the result of the previous analysis to the dark matter halo rotation curves of three different dwarfs, namely NGC 2976, known to have a flat inner core, NGC 5949 having a profile intermediate between a cored and a cuspy one, and NGC 5963 having a cuspy profile. After calculating baryon fraction, which is $\simeq 0.1$ for the three galaxies, we fitted the rotation curves changing the value of angular momentum. NGC 2976, has an higher value of ordered angular momentum ($λ\simeq 0.04$) with respect to NGC 5949 ($λ\simeq 0.025$) and in the case of NGC 5963 the very steep profile can be obtained with a low value of $λ$ ($λ\simeq 0.02$) and also decreasing the value of the random angular momentum. In the case of NGC 2976 tidal interaction with M81 could have also influenced the inner part of the density profile.

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arXiv2011

Secondary infall model and dark matter scaling relations in intermediate redshift early - type galaxies

Scaling relations among dark matter (DM) and stellar quantities are a valuable tool to constrain formation scenarios and the evolution of galactic structures. However, most of the DM properties are actually not directly measured, but derived through model dependent mass mapping procedures. It is therefore crucial to adopt theoretically and observationally well founded models. We use here an updated version of the secondary infall model (SIM) to predict the halo density profile, taking into account the effects of angular momentum, dissipative friction and baryons collapse. The resulting family of halo profiles depends on one parameter only, the virial mass, and nicely fits the projected mass and aperture velocity dispersion of a sample of intermediate redshift lens galaxies. We derive DM related quantities (namely the column density and the Newtonian acceleration) and investigate their correlations with stellar mass, luminosity, effective radius and virial mass.

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arXiv2011

Spherical galaxy models as equilibrium configurations in nonextensive statistics

Considering galaxies as self - gravitating systems of many collisionless particles allows to use methods of statistical mechanics inferring the distribution function of these stellar systems. Actually, the long range nature of the gravitational force contrasts with the underlying assumptions of Boltzmann statistics where the interactions among particles are assumed to be short ranged. A particular generalization of the classical Boltzmann formalism is available within the nonextensive context of Tsallis q -statistics, subject to non -additivity of the entropies of sub - systems. Assuming stationarity and isotropy in the velocity space, it is possible solving the generalized collsionless Boltzmann equation to derive the galaxy distribution function and density profile. We present a particular set of nonextensive models and investigate their dynamical and observable properties. As a test of the viability of this generalized context, we fit the rotation curve of M33 showing that the proposed approach leads to dark matter haloes in excellent agreement with the observed data.

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arXiv2010

On the universality of density profiles

We use the secondary infall model described in Del Popolo (2009), which takes into account the effect of dynamical friction, ordered and random angular momentum, baryons adiabatic contraction and dark matter baryons interplay, to study how in- ner slopes of relaxed LCDM dark matter (DM) halos with and without baryons (baryons+DM, and pure DM) depend on redshift and on halo mass. We apply the quoted method to structures on galactic scales and clusters of galaxies scales. We find that the inner logarithmic density slope, of dark matter halos with baryons has a significant dependence on halo mass and redshift with slopes ranging from 0 for dwarf galaxies to 0.4 for objects of M = 10^13M_solar and 0.94 for M = 10^15M_solar clusters of galaxies. Structures slopes increase with increasing redshift and this trend reduces going from galaxies to clusters. In the case of density profiles constituted just of dark matter the mass and redshift dependence of slope is very slight. In this last case, we used the Merrit et al. (2006) analysis who compared N-body density profiles with various parametric models finding systematic variation in profile shape with halo mass. This last analysis suggests that the galaxy-sized halos obtained with our model have a different shape parameter, i.e. a different mass distribution, than the cluster-sized halos, obtained with the same model. The results of the present paper argue against universality of density profiles constituted by dark matter and baryons and confirm claims of a systematic variation in profile shape with halo mass, for dark matter halos.

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arXiv2010

Improvements in the X-ray luminosity function and constraints on the Cosmological parameters from X-ray luminous clusters

We show how to improve constraints on Ω_m, σ_8, and the dark-energy equation-of-state parameter, w, obtained by Mantz et al. (2008) from measurements of the X-ray luminosity function of galaxy clusters, namely MACS, the local BCS and the REFLEX galaxy cluster samples with luminosities L> 3 \times 10^{44} erg/s in the 0.1--2.4 keV band. To this aim, we use Tinker et al. (2008) mass function instead of Jenkins et al. (2001) and the M-L relationship obtained from Del Popolo (2002) and Del Popolo et al. (2005). Using the same methods and priors of Mantz et al. (2008), we find, for a Λ$CDM universe, Ω_m=0.28^{+0.05}_{-0.04} and σ_8=0.78^{+0.04}_{-0.05}$ while the result of Mantz et al. (2008) gives less tight constraints $Ω_m=0.28^{+0.11}_{-0.07}$ and σ_8=0.78^{+0.11}_{-0.13}. In the case of a wCDM model, we find Ω_m=0.27^{+0.07}_{-0.06}, $σ_8=0.81^{+0.05}_{-0.06}$ and $w=-1.3^{+0.3}_{-0.4}$, while in Mantz et al. (2008) they are again less tight Ω_m=0.24^{+0.15}_{-0.07}, σ_8=0.85^{+0.13}_{-0.20} and w=-1.4^{+0.4}_{-0.7}. Combining the XLF analysis with the f_{gas}+CMB+SNIa data set results in the constraint Ω_m=0.269 \pm 0.012, σ_8=0.81 \pm 0.021 and w=-1.02 \pm 0.04, to be compared with Mantz et al. (2008), Ω_m=0.269 \pm 0.016, σ_8=0.82 \pm 0.03 and w=-1.02 \pm 0.06. The tightness of the last constraints obtained by Mantz et al. (2008), are fundamentally due to the tightness of the $f_{gas}$+CMB+SNIa constraints and not to their XLF analysis. Our findings, consistent with w=-1, lend additional support to the cosmological-constant model.

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arXiv2009

The Cusp/Core problem and the Secondary Infall Model

We study the cusp/core problem using a secondary infall model (SIM) that takes into account the effect of ordered and random angular momentum, dynamical friction and baryons adiabatic contraction. The model is applied to structures on galactic scales (normal and dwarfs spiral galaxies) and on clusters of galaxies scales. Our analysis suggest that angular momentum and dynamical friction are able, on galactic scales, to overcome the competing effect of adiabatic contraction eliminating the cusp. The slope of density profile of inner haloes flattens with decreasing halo mass and the profile is well approximated by a Burkert's profile. In order to obtain the NFW profile, starting from the profiles obtained from our model, the magnitude of angular momentum and dynamical friction must be reduced with respect to the values predicted by the model itself. The rotation curves of four LSB galaxies from Gentile et al. (2004) are compared to the rotation curves obtained by the model in the present paper obtaining a good fit to the observational data. The time evolution of the density profile of a galaxy of $10^8-10^9 M_{\odot}$ shows that after a transient steepening, due to the adiabatic contraction, the density profile flattens to $α\simeq 0$. On cluster scales we observe a similar evolution of the dark matter density profile but in this case the density profile slope flattens to $α\simeq 0.6$ for a cluster of $\simeq 10^{14} M_{\odot}$. The total mass profile, differently from that of dark matter, shows a central cusp well fitted by a NFW model.

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arXiv2009

Constraints on the Cosmological parameters by means of the clusters mass function

We present constraints on the values of $Ω_m$, $n$, $σ_8$, obtained from measurements of the X-ray luminosity function of galaxy clusters as compiled in EMSS, RDCS and BCS galaxy cluster samples. The values obtained $Ω_m=0.25^{+0.15}_{-0.05}$, $n=-1^{+0.05}_{-0.05}$, and $σ_8=0.8^{+0.1}_{-0.1}$ are in agreement with WMAP data. We then put constraints on the quoted parameters and the dark-energy equation-of-state parameter, $w$, using Chandra observations of 37 clusters with $ $=0.55 derived from 400 deg$^2$ ROSAT serendipitous survey and 49 brightest $z \simeq 0.05$ clusters detected in the All-Sky Survey. In the case of $Λ$CDM model, we get $Ω_m=0.25^{+0.1}_{-0.08}$ and $σ_8=0.75^{+0.08}_{-0.05}$, while in the case of the $w$CDM model, we get $Ω_m=0.28^{+0.10}_{-0.10}$, $w=-1.25^{+0.30}_{-0.35}$, and $σ_8=0.8^{+0.09}_{-0.09}$. Our results are consistent with those from recent analyses of type Ia supernovae, cosmic microwave background anisotropies, the X-ray gas mass fraction of relaxed galaxy clusters, baryon acoustic oscillations and cosmic shear. The improvement in data quality from EMSS, RDCS, and BCS to Chandra observations leads to an improvement in the constraints even if not of the same entity of the improvement in data.

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arXiv2009

Angular momentum transfer and the size - mass relation in early - type galaxies

Early - type galaxies (ETGs) define a narrow strip in the size - mass plane because of the observed correlation between the effective radius $R_{eff}$ and the total stellar mass $M_{\star}$. When expressed in logarithmic units, a linear relation, $\log{R_{eff}} \propto γ\log{M_{\star}}$, is indeed observationally found, but the slope $γ$ deviates from the canonical $γ= 1/2$ value which can be naively predicted for a spherically symmetric isotropic system. We propose here that a transfer of angular momentum to the stellar component induces an anisotropy in the velocity space thus leading to a modified distribution function (DF). Assuming an Osipkov - Merritt like anisotropic DF, we derive an analytic relation between the slope $γ$ of the size - mass relation and the slope $α$ of the angular momentum term in the DF. With this simple model, we are then able to recover the observed $γ$ value provided $α$ is suitably set. It turns out that an anisotropy profile which is tangential inside $\sim 0.6 r_a$ and radial outside, with $r_a$ the anisotropy radius, is able to reproduce the observed size - mass relation observed for massive ($M_{\star} \ge 2 \times 10^{10} \ h^{-1} {\rm M}_{\odot}$) elliptical galaxies.

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arXiv2009

Density profiles of dark matter haloes on Galactic and Cluster scales

In the present paper, we improve the "Extended Secondary Infall Model" (ESIM) of Williams et al. (2004) to obtain further insights on the cusp/core problem. The model takes into account the effect of ordered and random angular momentum, dynamical friction and baryon adiabatic contraction in order to obtain a secondary infall model more close to the collapse reality. The model is applied to structures on galactic scales (normal and dwarf spiral galaxies) and on cluster of galaxies scales. The results obtained suggest that angular momentum and dynamical friction are able, on galactic scales, to overcome the competing effect of adiabatic contraction eliminating the cusp. The NFW profile can be reobtained, in our model only if the system is constituted just by dark matter and the magnitude of angular momentum and dynamical friction are reduced with respect to the values predicted by the model itself. The rotation curves of four LSB galaxies from de Blok & Bosma (2002) are compared to the rotation curves obtained by the model in the present paper obtaining a good fit to the observational data. On scales smaller than $\simeq 10^{11} h^{-1} M_{\odot}$ the slope $α\simeq 0$ and on cluster scales we observe a similar evolution of the dark matter density profile but in this case the density profile slope flattens to $α\simeq 0.6$ for a cluster of $\simeq 10^{14} h^{-1} M_{\odot}$. The total mass profile, differently from that of dark matter, shows a central cusp well fitted by a NFW model.

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arXiv2008

On the nature of gravitational forces

In this paper I show how the statistics of the gravitational field is changed when the system is characterized by a non-uniform distribution of particles. I show how the distribution functions W(dF/dt) giving the joint probability that a test particle is subject to a force F and an associated rate of change of F given by dF/dt, are modified by inhomogeneity. Then I calculate the first moment of dF/dt to study the effects of inhomogenity on dynamical friction. Finally I test, by N-Body simulations, that the theoretical W(F) and dF/dt describes correctly the experimental data and I find that the stochastic force distribution obtained for the evolved system is in good agreement with theory. Moreover, I find that in an inhomogeneous background the friction force is actually enhanced relative to the homogeneous case.

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arXiv2006

On the cosmological mass function theory

This paper provides, from one side, a review of the theory of the cosmological mass function from a theoretical point of view, starting from the seminal paper of Press & Shechter (1974) to the last developments (Del Popolo & Gambera (1998, 1999), Sheth & Tormen 1999 (ST), Sheth, Mo & Tormen 2001 (ST1), Jenkins et al. 2001 (J01), Shet & Tormen 2002 (ST2), Del Popolo 2002a, Yagi et al. 2004 (YNY)), and from another side some improvements on the multiplicity function models in literature. ...

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