Quadruple-peaked spectral line profiles as a tool to constrain gravitational potential of shell galaxies

Stellar shells observed in many giant elliptical and lenticular as well as a few spiral and dwarf galaxies, presumably result from galaxy mergers. Line-of-sight velocity distributions of the shells could, in principle, if measured with a sufficiently high S/N, constitute one of methods to constrain the gravitational potential of the host galaxy. Merrifield & Kuijken (1998) predicted a double-peaked line profile for stationary shells resulting from a nearly radial minor merger. In this paper, we aim at extending their analysis to a more realistic case of expanding shells, inherent to the merging process, whereas we assume the same type of merger and the same orbital geometry. We use analytical approach as well as test particle simulations to predict the line-of-sight velocity profile across the shell structure. Simulated line profiles are convolved with spectral PSFs to estimate the peak detectability. The resulting line-of-sight velocity distributions are more complex than previously predicted due to non-zero phase velocity of the shells. In principle, each of the Merrifield & Kuijken (1998) peaks splits into two, giving a quadruple-peaked line profile, which allows more precise determination of the potential of the host galaxy and, moreover, contains additional information. We find simple analytical expressions that connect the positions of the four peaks of the line profile and the mass distribution of the galaxy, namely the circular velocity at the given shell radius and the propagation velocity of the shell. The analytical expressions were applied to a test-particle simulation of a radial minor merger and the potential of the simulated host galaxy was successfully recovered. The shell kinematics can thus become an independent tool to determine the content and distribution of the dark matter in shell galaxies, up to ~100 kpc from the center of the host galaxy.Comment: 15 pages, 16 figures | v2: accepted for publication in A&A, minor language correction

ADIABATIC SHEAR IN POROUS MEDIA

On propose un modèle avancé pour décrire la déformation de cisaillement qui se produit lors de la déformation à grande vitesse d'un solide poreux ductile réalisée par un simple chargement en cisaillement plan auquel est superposée une pression hydrodynamique. Afin de décrire un matériau thermoplastique rigide et poreux, on utilise la théorie de Gurson sur la plasticité en expansion. L'apparition d'un cisaillement adiabatique est interprétée en terme d'instabilités mathématiques dans les équations différentielles appropriées. On démontre l'influence substantielle de la porosité sur le durcissement et sur l'adoucissement thermique.An advanced model of shear deformation occuring in high strain rate deformation of ductile porous solids is proposed under simple planar shear loading superposed by hydrostatic pressure. To describe porous - rigid thermoplastic material the Gurson theory of dilatant plasticity is applied and appearance of an adiabatic shear is interpreted in terms of mathematical instabilities in the underlying differential equations. The substantial influence of porosity on strain hardening and thermal softening effects is demonstrated

THE INFLUENCE OF MIXED FERRITE-BAINITE MICROSTRUCTURE ON CRACK INITIATION UNDER DYNAMIC LOADING

Nous étudions l'influence de la microstructure mixte ferrite-bainite de l'acier C-Cr-Mo sur l'amorçage des fissures lors de chargements dynamiques. Trois techniques expérimentales différentes ont été employées pour évaluer le comportement en rupture dynamique de cet acier.A study of the influence of mixed ferrite-bainite microstructure of C-Cr-Mo steel on crack initiation under dynamic loading was performed. Three different experimental techniques were used to evaluate the dynamic fracture behaviour of the given steel

Study of gravitational fields and globular cluster systems of early-type galaxies

Context. Gravitational fields at the outskirts of early-type galaxies (ETGs) are difficult to constrain observationally. It thus remains poorly explored how well the ΛCDM and MOND hypotheses agree with ETGs. Aims. The dearth of studies on this topic motivated us to gather a large sample of ETGs and examine homogeneously which dark matter halos they occupy, whether the halos follow the theoretically predicted stellar-to-halo mass relation (SHMR) and the halo mass-concentration relation (HMCR), whether ETGs obey MOND and the radial acceleration relation (RAR) observed for late-type galaxies (LTGs), and finally whether ΛCDM or MOND perform better in ETGs. Methods. We employed Jeans analysis of radial velocities of globular clusters (GCs). We analysed nearly all ETGs having more than about 100 archival GC radial velocity measurements available. The GC systems of our 17 ETGs extend mostly over ten effective radii. A ΛCDM simulation of GC formation helped us to interpret the results. Results. Successful ΛCDM fits are found for all galaxies, but compared to the theoretical HMCR and SHMR, the best-fit halos usually have concentrations that are too low and stellar masses that are too high for their masses. This might be because of tidal stripping of the halos or because ETGs and LTGs occupy different halos. Most galaxies can be fitted by the MOND models successfully as well, but for some of the galaxies, especially those in centers of galaxy clusters, the observed GC velocity dispersions are too high. This might be a manifestation of the additional dark matter that MOND requires in galaxy clusters. Additionally, we find many signs that the GC systems were perturbed by galaxy interactions. Formal statistical criteria prefer the best-fit ΛCDM models over the MOND models, but this might be due to the higher flexibility of the ΛCDM models. The MOND approach can predict the GC velocity dispersion profiles better

Imprint of the galactic acceleration scale on globular cluster systems

International audienceWe report that the density profiles of globular cluster (GC) systems in a sample of 17 early-type galaxies (ETGs) show breaks at the radii where the gravitational acceleration exerted by the stars equals the galactic acceleration scale a 0 known from the radial acceleration relation or the modified Newtonian dynamics (MOND). The match with the other characteristic radii in the galaxy is not that close. We propose possible explanations in the frameworks of the Lambda cold dark matter (ΛCDM) model and MOND. We find tentative evidence that in the ΛCDM context, GCs reveal not only the masses of the dark halos through the richness of the GC systems but also the concentrations through the break radii of the GC systems