A constant dark matter halo surface density in galaxies

We confirm and extend the recent finding that the central surface density r_0*rho_0 galaxy dark matter halos, where r_0 and rho_0 are the halo core radius and central density, is nearly constant and independent of galaxy luminosity. Based on the co-added rotation curves of about 1000 spiral galaxies, mass models of individual dwarf irregular and spiral galaxies of late and early types with high-quality rotation curves and, galaxy-galaxy weak lensing signals from a sample of spiral and elliptical galaxies, we find that log(r_0*rho_0) = 2.15 +- 0.2, in units of log(Msol/pc^2). We also show that the observed kinematics of Local Group dwarf spheroidal galaxies are consistent with this value. Our results are obtained for galactic systems spanning over 14 magnitudes, belonging to different Hubble Types, and whose mass profiles have been determined by several independent methods. In the same objects, the approximate constancy of rho_0*r_0 is in sharp contrast to the systematical variations, by several orders of magnitude, of galaxy properties, including rho_0 and central stellar surface density.Comment: Accepted for publication in MNRAS. 9 pages, 4 figure

Analysis of Rotation Curves in the framework of R^n gravity

We present an analysis of a devised sample of Rotation Curves (RCs), aimed at checking the consequences of a modified f(R) gravity on galactic scales. Originally motivated by the the dark energy mystery, this theory may serve as a possibility of explaining the observed non-Keplerian profiles of galactic RCs in terms of a break-down of the Einstein General Relativity. We show that in general the power-law f(R) version could fit well the observations with reasonable values for the mass model parameters, encouraging further investigation on R^n gravity from both observational and theoretical points of view.Comment: Accepted for publication on Mon.Not.Roy.Astron.So

Probing the dark matter issue in f(R)-gravity via gravitational lensing

For a general class of analytic f(R)-gravity theories, we discuss the weak field limit in view of gravitational lensing. Though an additional Yukawa term in the gravitational potential modifies dynamics with respect to the standard Newtonian limit of General Relativity, the motion of massless particles results unaffected thanks to suitable cancellations in the post-Newtonian limit. Thus, all the lensing observables are equal to the ones known from General Relativity. Since f(R)-gravity is claimed, among other things, to be a possible solution to overcome for the need of dark matter in virialized systems, we discuss the impact of our results on the dynamical and gravitational lensing analyses. In this framework, dynamics could, in principle, be able to reproduce the astrophysical observations without recurring to dark matter, but in the case of gravitational lensing we find that dark matter is an unavoidable ingredient. Another important implication is that gravitational lensing, in the post-Newtonian limit, is not able to constrain these extended theories, since their predictions do not differ from General Relativity.Comment: 7 pages, accepted for publication in EPJ

Dark energy and dust matter phases from an exact f(R)f(R)-cosmology model

We show that dust matter-dark energy combined phases can be achieved by the exact solution derived from a power law $f(R)$ cosmological model. This example answers the query by which a dust-dominated decelerated phase, before dark-energy accelerated phase, is needed in order to form large scale structures.Comment: 6 pages, 5 figures. to appear in Phys. Lett.

The dark matter density at the Sun's location

Aims: We derive the value of the dark matter density at the Sun's location (ρ⊙) without fully modeling the mass distribution in the Galaxy. Methods: The proposed method relies on the local equation of centrifugal equilibrium and is independent of i) the shape of the dark matter density profile, ii) knowledge of the rotation curve from the galaxy center out to the virial radius, and iii) the uncertainties and the non-uniqueness of the bulge/disk/dark halo mass decomposition. Results: The result can be obtained in analytic form, and it explicitly includes the dependence on the relevant observational quantities and takes their uncertainties into account. By adopting the reference, state-of-the-art values for these, we find ρ ⊙ = 0.43(11)(10) GeV/cm3, where the quoted uncertainties are respectively due to the uncertainty in the slope of the circular-velocity at the Sun location and the ratio between this radius and the length scale of the stellar exponential thin disk. Conclusions: We obtained a reliable estimate of ρ⊙, that, in addition has the merit of being ready to take any future change/improvement into account in the measures of the observational quantities it depends on

Dark Matter Universal Properties in Galaxies

In the past years a wealth of observations has unraveled the structural properties of dark and luminous mass distribution in galaxies, a benchmark for understanding dark matter and the process of galaxy formation. The study of the kinematics of over thousand spirals has evidenced a dark-luminous matter coupling and the presence of a series of scaling laws, pictured by the Universal Rotation Curve paradigm, an intriguing observational scenario not easily explained by present theories of galaxy formation.Comment: Proceedings of the VI International Workshop on the Dark side of the Universe. June 01-06, 2010. Le\'on, M\'exic

f(R) theories

Over the past decade, f(R) theories have been extensively studied as one of the simplest modifications to General Relativity. In this article we review various applications of f(R) theories to cosmology and gravity - such as inflation, dark energy, local gravity constraints, cosmological perturbations, and spherically symmetric solutions in weak and strong gravitational backgrounds. We present a number of ways to distinguish those theories from General Relativity observationally and experimentally. We also discuss the extension to other modified gravity theories such as Brans-Dicke theory and Gauss-Bonnet gravity, and address models that can satisfy both cosmological and local gravity constraints.Comment: 156 pages, 14 figures, Invited review article in Living Reviews in Relativity, Published version, Comments are welcom

Equipos multiprofesionales-multidisciplinares en el ámbito educativo - legislación comparada y regulación de políticas educacionales en Argentina y Brasil

Las demandas al servicio/trabajo social por parte de las instituciones educacionales en Argentina y Brasil están asociadas al proceso histórico de establecimiento de la obligatoriedad escolar y la universalización del derecho a la educación. Esa obligatoriedad fue legislada por primera vez en 1884 en la Argentina a través de la Ley nº 1.420 (Bravo, 1988) y en la Constitución Federal de 1934 en el caso brasileño (Cury, 2007). Habría encontrado mayores dificultades para ser institucionalizada en el Brasil, debido a la histórica fuerza descentralizadora[1]. A pesar de ello y con base en la revisión de literatura realizada, podemos observar que en ambos países hubo una serie de etapas más o menos definidas en la relación entre la obligatoriedad escolar, la universalización de la educación básica, la situación de pobreza del alumnado y la institucionalización de servicios/trabajos sociales en el sistema educativo: etapa higienista, desarrollista, autoritaria y democratizadora/neoliberal.[1] “Nos países em que o sentido da educação esteve atrelado principalmente a uma política de integração, o Estado cumpriu um papel central na criação de um sistema educacional mais democrático, por meio de políticas de homogeneização e universalização da educação (...). Diferentemente de outros países, no Brasil o Estado nacional cumpriu um papel secundário, ficando a educação atrelada à formação de elites e às necessidades de um desenvolvimento industrial tardio e concentrado apenas em algumas regiões” (Krawczyk e Vieira, 2012:150)