Browsing by Subject "dark matter"

Now showing 1 - 6 of 6
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    Open Access
    Exploring the GalMer database: bar properties and non-circular motions
    (2016) Randriamampandry, T H; Deg, N; Carignan, C; Combes, F; Spekkens, K
    Context. We use Tree-SPH simulations from the GalMer database to characterize and quantify the non-circular motions induced by the presence of bar-like structures on the observed rotation curve of barred galaxies derived from empirical models of their line-of-sight velocity maps. The GalMer database consists of SPH simulations of galaxies spanning a wide range of morphological types and sizes.
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    Open Access
    Isolated and non-isolated dwarfs in terms of modified Newtonian dynamics
    (2012) Gentile, G; Angus, G W; Famaey, B; Oh, S-H; de Blok, W J G
    Within the framework of modified Newtonian dynamics (MOND), we investigate the kinematics of two dwarf spiral galaxies belonging to very different environments, namely KK 246 in the Local Void and Holmberg II in the M 81 group. A mass model of the rotation curve of KK 246 is presented for the first time, and we show that its observed kinematics are consistent with MOND. We re-derive the outer rotation curve of Holmberg II, by modelling its HI data cube, and find that its inclination should be closer to face-on than previously derived. This implies that Holmberg II has a higher rotation velocity in its outer parts, which, although not very precisely constrained, is consistent with the MOND prediction.
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    Open Access
    Mass models of disc galaxies from the DiskMass Survey in modified Newtonian dynamics
    (2015) Angus, G W; Gentile, G; Swaters, R; Famaey, B; Diaferio, A; McGaugh, S S; Heyden, K J van der
    This article explores the agreement between the predictions of modified Newtonian dynamics (MOND) and the rotation curves and stellar velocity dispersion profiles measured by the DiskMass Survey (DMS). A bulge-disk decomposition was made for each of the thirty published galaxies, and a MOND Poisson solver was used to simultaneously compute, from the baryonic mass distributions, model rotation curves and vertical velocity dispersion profiles, which were compared to the measured values. The two main free parameters, the stellar disk's mass-to-light ratio (M/L) and its exponential scaleheight (h(z)), were estimated by Markov Chain Monte Carlo modelling. The average best-fitting K-band stellar mass-to-light ratio was M/L a parts per thousand integral 0.55 +/- A 0.15. However, to match the DMS data, the vertical scaleheights would have to be in the range h(z) = 200-400 pc which is a factor of 2 lower than those derived from observations of edge-on galaxies with a similar scalelength. The reason is that modified gravity versions of MOND characteristically require a larger M/L to fit the rotation curve in the absence of dark matter and therefore predict a stronger vertical gravitational field than Newtonian models. It was found that changing the MOND acceleration parameter, the shape of the velocity dispersion ellipsoid, the adopted vertical distribution of stars, as well as the galaxy inclination, within any realistic range, all had little impact on these results.
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    Open Access
    pFoF: a highly scalable halo-finder for large cosmological data sets
    (2014) Roy, Fabrice; Bouillot, Vincent R; Rasera, Yann
    We present a parallel implementation of the friends-of-friends algorithm and an innovative technique for reducing complex-shaped data to a user-friendly format. This code, named pFoF, contains an optimized post-processing workflow that reduces the input data coming from gravitational codes, arranges them in a user-friendly format and detects groups of particles using percolation and merging methods. The pFoF code also allows for detecting structures in sub- or non-cubic volumes of the comoving box. In addition, the code offers the possibility of performing new halo-findings with a lower percolation factor, useful for more complex analysis. In this paper, we give standard test results and show performance diagnostics to stress the robustness of pFoF. This code has been extensively tested up to 32768 MPI processes and has proved to be highly scalable with an efficiency of more than 75%. It has been used for analysing the Dark Energy Universe Simulation: Full Universe Runs (DEUS-FUR) project, the first cosmological simulations of the entire observable Universe, modelled with more than half a trillion dark matter particles.
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    The baryonic Tully-Fisher relation and its implication for dark matter halos
    (2009) Trachternach, C; de Blok, W J G; McGaugh, S S; van der Hulst, J M; Dettmar, R-J
    The baryonic Tully-Fisher relation (BTF) is a fundamental relation between baryonic mass and maximum rotation velocity. It can be used to estimate distances, as well as to constrain the properties of dark matter and its relation with the visible matter.
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    THINGS about MOND
    (2011) Gentile, G; Famaey, B; de Blok, W J G
    We present an analysis of 12 high-resolution galactic rotation curves from The HI Nearby Galaxy Survey (THINGS) in the context of modified Newtonian dynamics (MOND). These rotation curves were selected to be the most reliable for mass modelling, and they are the highest quality rotation curves currently available for a sample of galaxies spanning a wide range of luminosities. We fit the rotation curves with the "simple" and "standard" interpolating functions of MOND, and we find that the "simple" function yields better results. We also redetermine the value of a(0), and find a median value very close to the one determined in previous studies, a(0) = (1.22 +/- 0.33) x 10(-8) cm s(-2). Leaving the distance as a free parameter within the uncertainty of its best independently determined value leads to excellent quality fits for 75% of the sample. Among the three exceptions, two are also known to give relatively poor fits in Newtonian dynamics plus dark matter. The remaining case (NGC 3198) presents some tension between the observations and the MOND fit, which might, however, be explained by the presence of non-circular motions, by a small distance, or by a value of a(0) at the lower end of our best-fit interval, 0.9 x 10(-8) cm s(-2). The best-fit stellar M/L ratios are generally in remarkable agreement with the predictions of stellar population synthesis models. We also show that the narrow range of gravitational accelerations found to be generated by dark matter in galaxies is consistent with the narrow range of additional gravity predicted by MOND.