arXiv subjects

A. Del Popolo

Publications and source records attributed to A. Del Popolo.

At least 109 records · Page 6Linked to original sources

arXiv2006

Gravitational collapse and non-self similarity in the L-T relation

We derive the luminosity-temperature relation for clusters of galaxies by means of a modification of the self-similar model to take account of angular momentum acquisition by protostructures and of an external pressure term in the virial theorem. The fundamental result of the model is that gravitational collapse, which takes account of angular momentum acquisition, can explain the non self-similarity in the L-T relation, in disagreement with the largely accepted assumption that heating/cooling processes and similar are fundamental in the originating the non-self similar behavior (shaping) of the L-T relation.

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arXiv2006

On the Average Comoving Number Density of Halos

I compare the numerical multiplicity function given in Yahagi, Nagashima & Yoshii (2004) with the theoretical multiplicity function obtained by means of the excursion set model and an improved version of the barrier shape obtained in Del Popolo & Gambera (1998), which implicitly takes account of total angular momentum acquired by the proto-structure during evolution and of a non-zero cosmological constant. I show that the multiplicity function obtained in the present paper, is in better agreement with Yahagi, Nagashima & Yoshii (2004) simulations than other previous models (Sheth & Tormen 1999; Sheth, Mo & Tormen 2001; Sheth & Tormen 2002; Jenkins et al. 2001) and that differently from some previous multiplicity function models (Jenkins et al. 2001; Yahagi, Nagashima & Yoshii 2004) it was obtained from a sound theoretical background.

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arXiv2006

Evolution of the cosmological mass function in a moving barrier model

I calculate the mass function evolution in a $Λ$CDM model by means of the excursion set model and an improved version of the barrier shape obtained in Del Popolo & Gambera (1998), which implicitly takes account of the total angular momentum acquired by the proto-structure during evolution and of a non-zero cosmological constant. I compare the result with Reed et al. (2003), who used a high resolution $Λ$CDM numerical simulation to calculate the mass function of dark matter haloes down to the scale of dwarf galaxies, back to a redshift of fifteen. I show that the mass function obtained in the present paper, gives similar predictions to the Sheth & Tormen mass function but it does not show the overprediction of extremely rare objects shown by the Sheth and Tormen mass function. The results confirm previous findings that the simulated halo mass function can be described solely by the variance of the mass distribution, and thus has no explicit redshift dependence.

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arXiv2006

Measuring Omega_m using clusters evolution

The constraints obtained by several authors (Eke et al. 1998; Henry 2000) on the estimated values of $Ω_{\rm m}$, $n$ and $σ_8$ are revisited in the light of recent theoretical developments: 1) new theoretical mass functions; 2) a more accurate mass-temperature relation, also determined for arbitrary $Ω_{\rm m}$ and $Ω_{\rm Λ}$. I re-derive the X-ray Temperature Function (XTF), similarly to Henry (2000) and Eke et al. (1999), re-obtaining the constraints on $Ω_{\rm m}$, $n$, $σ_8$. The result shows that changes in the mass function and M-T relation produces an increase in $Ω_{\rm m}$ of $ \simeq 20%$ and similar results in $σ_8$ and $n$.

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arXiv2005

Constraints on cosmological parameters through clusters XLF and XTF

In this paper, I revisit the constraints obtained by several authors (Reichart et al. 1999; Eke et al. 1998; Henry 2000) on the estimated values of $Ω_{\rm m}$, $n$ and $σ_8$ in the light of recent theoretical developments: 1) new theoretical mass functions (Sheth & Tormen 1999, Sheth, Mo & Tormen 2001, Del Popolo 2002b); 2) a more accurate mass-temperature relation, also determined for arbitrary $Ω_{\rm m}$ and $Ω_{\rm Λ}$ (Del Popolo 2002a). Firstly, using the quoted improvements, I re-derive an expression for the X-ray Luminosity Function (XLF), similarly to Reichart et al. (1999), and then I get some constraints to $Ω_{\rm m}$ and $n$, by using the {\it ROSAT} BCS and {\rm EMSS} samples and maximum-likelihood analysis. Then I re-derive the X-ray Temperature Function (XTF), similarly to Henry (2000), re-obtaining the constraints on $Ω_{\rm m}$, $n$, $σ_8$. Both in the case of the XLF and XTF, the changes in the mass function and M-T relation produces an increase in $Ω_{\rm m}$ of $ \simeq 20%$ and similar results in $σ_8$ and $n$.

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arXiv2005

Orbital migration and the period distribution of exoplanets

We use the model for the migration of planets introduced in Del Popolo, Yesilyurt & Ercan (2003) to calculate the observed mass and semimajor axis distribution of extra-solar planets. The assumption that the surface density in planetesimals is proportional to that of gas is relaxed, and in order to describe disc evolution we use a method which, using a series of simplifying assumptions, is able to simultaneously follow the evolution of gas and solid particles for up to $10^7 {\rm yr}$. The distribution of planetesimals obtained after $10^7 {\rm yr}$ is used to study the migration rate of a giant planet through the model of this paper. The disk and migration models are used to calculate the distribution of planets as function of mass and semimajor axis. The results show that the model can give a reasonable prediction of planets' semi-major axes and mass distribution. In particular there is a pile-up of planets at $a \simeq 0.05$ AU, a minimum near 0.3 AU, indicating a paucity of planets at that distance, and a rise for semi-major axes larger than 0.3 AU, out to 3 AU. The semi-major axis distribution shows that the more massive planets (typically, masses larger than $4 M_{\rm J}$) form preferentially in the outer regions and do not migrate much. Intermediate-mass objects migrate more easily whatever the distance they form, and that the lighter planets (masses from sub-Saturnian to Jovian) migrate easily.

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arXiv2005

Cosmological constraints from clustering properties of galaxy clusters

In this paper, we discuss improvements of the Suto et al. (2000) model, in the light of recent theoretical developments (new theoretical mass functions, a more accurate mass-temperature relation and an improved bias model) to predict the clustering properties of galaxy clusters and to obtain constraints on cosmological parameters. We re-derive the two-point correlation function of clusters of galaxies for OCDM and LambdaCDM cosmological models, and we compare these results with the observed spatial correlation function for clusters in RASS1 (ROSAT All-Sky Survey 1), and in XBACs (X-RAY Brighest Abell-Type) samples. The comparison shows that the best agreement is obtained for the LambdaCDM model with Omega=0.3. The values of the correlation length obtained, (r_\simeq 28.2 \pm 5.2 \rm h^{-1}} Mpc for LambdaCDM), are larger than those found in the literature and comparable with the results found in Borgani, Plionis & Kolokotronis (1999). (REST IN THE PAPER ABSTRACT)

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arXiv2005

A theoretical study of the luminosity temperature relation for clusters of galaxies

A luminosity-temperature relation for clusters of galaxies is derived. The two models used, take into account the angular momentum acquisition by the proto-structures during their expansion and collapse. The first one is a modification of the self-similar model (SSM) while the second one is a modification of the Punctuated Equilibria Model (Cavaliere et al. 1999). In both models the mass-temperature relation (M-T) used is based on the calculations of Del Popolo (2002b). We show that the above models lead, in X-rays, to a luminosity-temperature relation that scales as L \propto T^5, at scale of groups, flattening to L \propto T^3 for rich clusters and converging to L \propto T^2 at higher temperatures. However a fundamental result of our paper is that the non-similarity in the L-T relation, can be explained by a simple model that takes into account the amount of the angular momentum of a proto-structure. This result is in disagreement with the widely accepted idea that the above non-similarity is due to non-gravitating processes as those of heating/cooling.

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arXiv2005

On the reliability of merger-trees and the mass growth histories of dark matter haloes

We have used merger trees realizations to study the formation of dark matter haloes. The construction of merger-trees is based on three different pictures about the formation of structures in the Universe. These pictures include: the spherical collapse (SC), the ellipsoidal collapse (EC) and the non-radial collapse (NR). The reliability of merger-trees has been examined comparing their predictions related to the distribution of the number of progenitors, as well as the distribution of formation times, with the predictions of analytical relations. The comparison yields a very satisfactory agreement. Subsequently, >.........

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arXiv2004

Constraints to cosmological parameters through clusters evolution

In this paper, I revisit the constraints obtained by several authors (Reichart et al. 1999; Eke et al. 1998; Henry 2000) on the estimated values of Omegam, n and sigma_8 in the light of recent theoretical developments: 1) new theoretical mass functions (Sheth & Tormen 1999, Sheth, Mo & Tormen 2001, Del Popolo 2002b); 2) a more accurate mass-temperature relation, also determined for arbitrary Omega_m and Omega_Lambda (Del Popolo 2002a).

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arXiv2004

Dark Matter Halos in a Secondary Infall Model

We calculate the density profiles of virialized halos in the case of structure evolving hierarchically from a scale-free Gaussian delta-field having a power spectrum $P(k)\propto k^n$ in a Omega=1 Universe; we suppose that the initial density contrast profile around local maxima is given by the mean peak profile introduced by Bardeen et al. (1986 hereafter BBKS). We show both that the density profiles are not power-laws but have a logarithmic slope that increases from the inner halo to its outer parts and for n \geq -1 are well approximated by Navarro et al. (1995, 1996, 1997) profile and the radius a, at which the slope alpha=-2, is a function of the mass of the halo and of the spectral index n.

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arXiv2004

X-ray temperature distribution function of clusters in presence of large non-radial motions

We consider the non-radial motions, originating in the outskirts of clusters of galaxies and we show how it may reduce the discrepancy between Cold Dark Matter (CDM) predicted X-ray temperature distribution function of clusters of galaxies and that really observed, so resolving the problem of the X-ray clusters abundance over-production predicted by the CDM model. We construct the X-ray temperature distribution function using Press-Schechter's (1974) theory and Evrard's (1990) prescriptions for the mass-temperature relation, taking also account of the non-radial motions originating from the gravitational interaction of the quadrupole moment of the protocluster. Then, we compare our X-ray temperature distribution function with the tidal field of the matter of the neighboring protostructures. We find that the model produces a reasonable cluster temperature distribution.

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arXiv2003

Improvements in the M-T relation and mass function and the measured Omega_m through clusters evolution

In this paper, I revisit the constraints obtained by several authors (Reichart et al. 1999; Eke et al. 1998; Henry 2000) on the estimated values of Omega_m, n and sigma_8 in the light of recent theoretical developments: 1) new theoretical mass functions (Sheth & Tormen 1999, Sheth, Mo & Tormen 1999, Del Popolo 2002b); 2) a more accurate mass-temperature relation, also determined for arbitrary Omega_m and Omega_Λ (Voit 2000, Pierpaoli et al. 2001, Del Popolo 2002a). Firstly, using the quoted improvements, I re-derive an expression for the X-ray Luminosity Function (XLF), similarly to Reichart et al. (1999), and then I get some constraints to Ω_m and n, by using the ROSAT BCS and EMSS samples and maximum-likelihood analysis. Then I re-derive the X-ray Temperature Function (XTF), similarly to Henry (2000) and Eke et al. (1999), re-obtaining the constraints on Omega_m, n, sigma_8. Both in the case of the XLF and XTF, the changes in the mass function and M-T relation produces an increase in Omega_m of \simeq 20% and similar results in sigma_8 and n.

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arXiv2003

Planetary migration in evolving planetesimals discs

In the current paper, we further improved the model for the migration of planets introduced in Del Popolo et al. (2001) and extended to time-dependent planetesimal accretion disks in Del Popolo and Eksi (2002). In the current study, the assumption of Del Popolo and Eksi (2002), that the surface density in planetesimals is proportional to that of gas, is released. In order to obtain the evolution of planetesimal density, we use a method developed in Stepinski and Valageas (1997) which is able to simultaneously follow the evolution of gas and solid particles for up to 10^7 yrs. Then, the disk model is coupled to migration model introduced in Del Popolo et al. (2001) in order to obtain the migration rate of the planet in the planetesimal. We find that the properties of solids known to exist in protoplanetary systems, together with reasonable density profiles for the disk, lead to a characteristic radius in the range 0.03-0.2 AU for the final semi-major axis of the giant planet.

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arXiv2003

Numerical tests of dynamical friction in gravitational inhomogeneous systems

In this paper, I test by numerical simulations the results of Del Popolo & Gambera (1998),dealing with the extension of Chandrasekhar and von Neumann's analysis of the statistics of the gravitational field to systems in which particles (e.g., stars, galaxies) are inhomogeneously distributed. The paper is an extension of that of Ahmad & Cohen (1974), in which the authors tested some results of the stochastic theory of dynamical friction developed by Chandrasekhar & von Neumann (1943) in the case of homogeneous gravitational systems. It is also a continuation of the work developed in Del Popolo (1996a,b), which extended the results of Ahmad & Cohen (1973), (dealing with the study of the probability distribution of the stochastic force in homogeneous gravitational systems) to inhomogeneous gravitational systems. Similarly to what was done by Ahmad & Cohen (1974) in the case of homogeneous systems, I test, by means of the evolution of an inhomogeneous system of particles, that the theoretical rate of force fluctuation d F/dt describes correctly the experimental one, I find that the stochastic force distribution obtained for the evolved system is in good agreement with the Del Popolo & Gambera (1998) theory. Moreover, in an inhomogeneous background the friction force is actually enhanced relative to the homogeneous case.

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arXiv2003

Planetary migration in protoplanetary disks

In the current paper, we further develop the model for the migration of planets introduced in Del Popolo et al. (2001) and extended to time-dependent accretion discs in Del Popolo and Eksi (2002). We use a method developed by Stepinski and Valageas (1996, 1997), that is able to simultaneously follow the evolution of gas and solid particles for up to $10^7 {\rm yr}$. The disc model is coupled to the migration model introduced in Del Popolo et al. (2001) in order to obtain the migration rate of the planet in the planetesimal disc. We find that in the case of discs having total mass of $10^{-3}-0.1 M_{\odot}$, and $0.1<α<0.0001$, planets can migrate inward a large distance while if $M<10^{-3} M_{\odot}$ the planets remain almost in their initial position for $0.1<α<0.01$ and only in the case $α<0.001$ the planets move to a minimum value of orbital radius of $\simeq 2 {\rm AU}$. The model gives a good description of the observed distribution of planets in the period range 0-20 days.

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arXiv2003

Evolution of planetesimal discs and planets migration

In this paper, we further develop the model for the migration of planets introduced in Del Popolo, Gambera and Ercan, and extended to time-dependent planetesimal accretion disks in Del Popolo and Eksi. More precisely, the assumption of Del Popolo and Eksi that the surface density in planetesimals is proportional to that of gas is released. Indeed, the evolution of the radial distribution of solids is governed by many processes: gas-solid coupling, coagulation, sedimentation, evaporation/condensation, so that the distribution of planetesimals emerging from a turbulent disk does not necessarily reflect that of gas. In order to describe this evolution we use a method developed in Stepinski and Valageas which, using a series of simplifying assumptions, is able to simultaneously follow the evolution of gas and solid particles for up to $10^7 {\rm yr}$. Then, the distribution of planetesimals obtained after $10^7 {\rm yr}$ is used to study the migration rate of a giant planet through the migration model introduced in \cite{DP1}. This allows us to investigate the dependence of the migration rate on the disk mass, on its time evolution and on the value of the dimensionless viscosity parameter alpha. We find that in the case of disks having a total mass of $10^{-3}-10^{-1} M_{\odot}$, and $10^{-4}<α<10^{-1}$, planets can migrate inward over a large distance while if $M_{\rm d}<10^{-3} M_{\odot}$ the planets remain almost at their initial position for $α>10^{-3}$ and only in the case $α<10^{-3}$ the planets move to a minimum value of orbital radius of $\simeq 2 {\rm AU}$. Moreover, the observed distribution of planets in the period range 0-20 days can be easily obtained from our model.

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arXiv2002

Dynamical derivation of Bode's law

In a planetary or satellite system, idealized as n small bodies in initially coplanar, concentric orbits around a large central body, obeying Newtonian point-particle mechanics, resonant perturbations will cause dynamical evolution of the orbital radii except under highly specific mutual relationships, here derived analytically apparently for the first time. In particular, the most stable situation is achieved (in this idealized model) only when each planetary orbit is roughly twice as far from the Sun as the preceding one, as observed empirically already by Titius (1766) and Bode (1778) and used in both the discoveries of Uranus (1781) and the Asteroid Belt (1801). ETC.

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