1,721,232 research outputs found
Low surface brightness galaxy rotation curves in the low energy limit of Rn gravity: No need for dark matter?
No full textWe investigate the possibility that the observed flatness of the rotation curves of spiral galaxies is not evidence for the existence of dark matter haloes, but rather a signal of the breakdown of General Relativity. To this aim, we consider power-law fourth-order theories of gravity obtained by replacing the scalar curvature R with f(R) = f0 Rn in the gravity Lagrangian. We show that, in the low energy limit, the gravitational potential generated by a point-like source may be written as φ(r) α r -1[1 + (r/rc)β] with β a function of the slope n of the gravity Lagrangian and rc a scalelength depending on the gravitating system properties. In order to apply the model to realistic systems, we compute the modified potential and the rotation curve for spherically symmetric and for thin disc mass distributions. It turns out that the potential is still asymptotically decreasing, but the corrected rotation curve, although not flat, is higher than the Newtonian one, thus offering the possibility to fit rotation curves without dark matter. To test the viability of the model, we consider a sample of 15 low surface brightness galaxies with combined H I and Hα measurements of the rotation curve extending in the putative dark matter dominated region. We find a very good agreement between the theoretical rotation curve and the data using only stellar disc and interstellar gas when the slope n of the gravity Lagrangian is set to the value n = 3.5 (giving β = 0.817) obtained by fitting the Type la supernova Hubble diagram with the assumed power-law f(R) model and no dark matter. The excellent agreement between theoretical and observed rotation curves and the values of the stellar mass-to-light ratios in agreement with the predictions of population synthesis models make us confident that Rn gravity may represent a good candidate to solve both the dark energy problem on cosmological scales and the dark matter one on galactic scales with the same value of the slope n of the higher-order gravity Lagrangian. © 2007 RAS
Some astrophysical implications of dark matter and gas profiles in a new galaxy cluster model
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Jointly fitting weak lensing, x-ray, and Sunyaev-Zel'dovich data to constrain scalar-tensor theories with clusters of galaxies
Full text linkDegenerate higher-order scalar-tensor (DHOST) theories are considered the most general class of scalar-tensor theories with an additional scalar field. DHOST theories modify the laws of gravity even at galaxy clusters scale hence affecting the weak lensing, x-ray, and Sunyaev-Zel'dovich observables. We derive the theoretical expression for the lensing convergence κ and the pressure profile P of clusters in the framework of DHOST theories and quantify how much they deviate from their general relativity counterparts. We argue that combined measurements of κ, P, and of the electron number density ne can constrain both the cluster parameters and some effective parameters of the DHOST theory. We carry on a Fisher matrix forecasts analysis to investigate whether this is indeed the case considering different scenarios for the spatial resolution and errors on the measured quantities
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