The present paper extends a previous study of Del Popolo to clusters of galaxies, considering how baryon-dark matter (DM) interplay shapes the density profiles of dwarf galaxies. Cluster density ...profiles are determined taking into account dynamical friction, random and ordered angular momentum and the response of DM haloes to condensation of baryons. We find that haloes containing only DM are characterized by Einasto's profiles, and that profiles flatten with increasing content of baryons and increasing values of random angular momentum. The analytical results obtained in the first part of the paper are applied to well-studied clusters, the inner profiles of which have slopes flatter than Navarro, Frenk & White (NFW) predictions (A611, A383) or are characterized by profiles in agreement with the NFW model (MACS J1423.8+2404, RXJ1133). By using an independently measured baryonic fraction and a typical spin parameter value λ≃ 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 ≃10 kpc, M
b, in, is correlated with the total mass of the clusters as
.
In this article, we test the conclusion of the universality of the dark matter (DM) halo surface density μ0D = ρ0
r
0. According to our study, the dispersion of values of μ0D is twice as high as that ...found previously by other authors. We conclude that the DM surface density and its Newtonian acceleration are not constant but correlate with the luminosity, morphological type, (B − V)0 colour index and content of neutral hydrogen. These DM parameters are higher for more luminous systems of early types with red colour and low gas content. We also found that the correlation of DM parameters with colour index appears to be the manifestation of a stronger relation between DM halo mass and the colour of a galaxy. This finding is in agreement with cosmological simulations. These results leave little room for the recently claimed universality of DM column density. We also found that isolated galaxies in our sample (contained in the Analysis of the interstellar Medium of Isolated GAlaxies (AMIGA) catalogue) do not differ significantly in their value of μ0D from the entire sample. Thus, since the AMIGA catalogue gives a sample of galaxies that have not interacted with a significant mass neighbour in the past 3 Gyr, the difference between systems with low and high values of μ0D is not related to merging events during this period of time.
In this paper, we analysed the correlation between the central surface density and the halo core radius of galaxies, and cluster of galaxies dark matter (DM) haloes, in the framework of the secondary ...infall model. We used Del Popolo secondary infall model taking into account ordered and random angular momentum, dynamical friction and 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
* (the halo characteristic radius) is not a universal quantity as claimed by Donato et al. and Gentile et al. On the contrary, we find a correlation with the halo mass M
200 in agreement with Cardone & Tortora, Boyarsky et al. and Napolitano, Romanowsky & Tortora, but with a significantly smaller scatter, namely 0.16 ± 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 of α = 0.18 ± 0.05. In the case of the surface density of DM for a system composed only of DM, as in dissipationless simulations, we get α = 0.20 ± 0.05. These results leave little room for the recently claimed universality of (dark and stellar) column density.
In this paper, we study how the dark matter density profiles of dwarf galaxies in the mass range 108-1010 M⊙ are modified by the interaction of the dwarf galaxy with neighbouring structures, and by ...the changing baryon fraction in dwarf galaxies. With this aim, and referring to an earlier paper by Del Popolo, we determine the density profiles of the dwarf galaxies, taking into account the effect of tidal interaction with neighbouring structures, the effects of ordered and random angular momentum, dynamical friction, the response of dark matter haloes to the condensation of baryons and the effects produced by the presence of baryons. As already shown in the earlier paper, the slope of the density profile of inner haloes flattens with decreasing halo mass, and the profile is well approximated by a Burkert profile. We thus treat the angular momentum generated by tidal torques and the baryon fraction as a parameter in order to understand how the latter influences the density profiles. The analysis shows that dwarf galaxies that have suffered a smaller tidal torque (and consequently have smaller angular momentum) are characterized by steeper profiles with respect to dwarf galaxies subject to higher torque. Similarly, dwarf galaxies that have a smaller baryon fraction also have steeper profiles than those that have a larger baryon fraction. When tidal torquing is shut down and baryons are not present, the density profile is very well approximated by an Einasto profile, similarly to dwarf galaxies obtained in dissipationless N-body simulations. Then, we apply the result of the previous analysis to the dark matter halo rotation curves of three different dwarfs: NGC 2976, which is known to have a flat inner core; NGC 5949, which has a profile intermediate between a cored and a cuspy one; and NGC 5963, which has a cuspy profile. After calculating the baryon fraction, which is ≃0.1 for the three galaxies, we fitted the rotation curves, changing the value of the angular momentum. NGC 2976 has a higher value of ordered angular momentum (λ≃ 0.04) than NGC 5949 (λ≃ 0.025). For NGC 5963, a very steep profile can be obtained with a low value of λ (λ≃ 0.02) and also by decreasing the value of the random angular momentum. For NGC 2976, the tidal interaction with M81 could also have influenced the inner part of the density profile. Finally, we show how the inner density profile correlates with the tidal index for dwarf and low surface brightness galaxies given by Karachentsev et al.
We study the cusp/core problem using a secondary infall model that takes into account the effect of ordered and random angular momentum, dynamical friction, and baryons adiabatic contraction (AC). ...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 AC eliminating the cusp. The slope of density profile of inner halos flattens with decreasing halo mass and the profile is well approximated by a Burkert's profile. In order to obtain the Navarro-Frenk-White (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 lower sideband galaxies from Gentile et al. 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 108-109 M shows that after a transient steepening, due to the AC, the density profile flattens to alpha 0. On cluster scales we observe a similar evolution of the dark matter (DM) density profile but in this case the density profile slope flattens to alpha 0.6 for a cluster of 1014 M . The total mass profile, differently from that of DM, shows a central cusp well fitted by an NFW model.
The consideration of galaxies as self-gravitating systems of many collisionless particles allows us to use methods of statistical mechanics for 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 non-extensive context of Tsallis q-statistics, subject to the non-additivity of the entropies of subsystems. Assuming stationarity and isotropy in the velocity space, when solving the generalized collisionless Boltzmann equation it is possible to derive the galaxy distribution function and density profile. We present a particular set of non-extensive models and we 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.
ABSTRACT
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 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 catalogue of 58 objects with estimated values of the B‐band absolute magnitude MB, the virial mass Mvir, and the DM and baryonic Newtonian accelerations (denoted as gDM(r0) and gbar(r0), respectively) within the scale radius r0 which we use to investigate whether it is possible to define a universal acceleration scale. We find a weak but statistically meaningful correlation with Mvir 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.
On the universality of density profiles Del Popolo, A.
Monthly notices of the Royal Astronomical Society,
November 2010, Letnik:
408, Številka:
3
Journal Article
Recenzirano
Odprti dostop
The secondary infall model (described in a previous paper by this author), which takes into account the effect of dynamical friction, ordered and random angular momentum, baryon adiabatic contraction ...and dark matter (DM) baryon interplay, is used to study how the inner slopes of relaxed ΛCDM haloes with and without baryons (baryons+DM and pure DM) depend on redshift and on halo mass. This method is applied to structures on galactic scales and clusters of galaxies scales. It is found that the inner logarithmic density slope, α≡ d log ρ/d log r, of DM haloes with baryons has a significant dependence on halo mass and redshift, with slopes ranging from α≃ 0 for dwarf galaxies to α≃ 0.4 for objects of M≃ 1013 M⊙ and α≃ 0.94 for M≃ 1015 M⊙ clusters of galaxies. Structure slopes increase with increasing redshift, and this trend reduces going from galaxies to clusters. In the case of density profiles constituted just of DM, the mass and redshift dependence of the slope are very slight. In this last case, the analysis of Merritt et al. is used. They compared N-body density profiles with various parametric models, finding systematic variation in the profile shape with halo mass. This last analysis suggests that the galaxy-sized haloes obtained with this model have a different shape parameter (i.e. a different mass distribution) than the cluster-sized haloes obtained with the same model. The results of the present paper argue against universality of density profiles constituted by DM and baryons and confirm the claims of a systematic variation in profile shape with halo mass, for DM haloes.
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