Kinematics of disc galaxies using photometrically calibrated N-body models

We have studied the evolution of isolated galaxies over several Gyr using a self-consistent N-body code including stars, gas and star formation. The results of our simulations are calibrated using spectrophotometric evolution models. We thus simultaneously analyse kinematical and photometrical evolution of the various stellar populations born during the successive bursts of star formation. Our calibrated simulations show that the properties of stellar velocity dispersion drops observed in the centre of three barred active galaxies by Emsellem et al. (2001) could depend on the observational wavelength. This revised version was published online in August 2006 with corrections to the Cover Date.     

S0 galaxies in Fornax: data and kinematics

We have obtained long-slit spectroscopy for a sample of nine S0 galaxies in the Fornax Cluster using the FORS2 spectrograph at the 8.2-m European Southern Observatory (ESO) Very Large Telescope (VLT). From these data, we have extracted the kinematic parameters, comprising the mean velocity, velocity dispersion and higher moment h ₃ and h ₄ coefficients, as a function of position along the major axes of these galaxies. Comparison with published kinematics indicates that earlier data are often limited by their lower signal-to-noise ratio and relatively poor spectral resolution. The greater depth and higher dispersion of the new data mean that we reach well beyond the bulges of these systems, probing their disc kinematics in some detail for the first time. Qualitative inspection of the results for individual galaxies shows that they are not entirely simple systems, perhaps indicating a turbulent past. None the less, we are able to derive reliable circular velocities for most of these systems, which points the way towards a study of their Tully–Fisher relation. This study, along with an analysis of the stellar populations of these systems out to large galactocentric distances, will form the bases of future papers exploiting these new high-quality data, hopefully shedding new light on the evolutionary history of these systems.     

Shapes of clusters and groups of galaxies: comparison of model predictions with observations

We study the properties of the three-dimensional and projected shapes of haloes using high-resolution numerical simulations and observational data where the latter comes from the 2PIGG [2dFGRS (2-degree Field Galaxy Redshift Survey) Percolation Inferred Galaxy Groups] and Data Release 3 of the Sloan Digital Sky Survey (SDSS-DR3GC) group catalogues. We investigate the dependence of the halo shape on characteristics such as mass and number of members. In the three-dimensional case, we find a significant correlation between the mass and the halo shape; massive systems are more prolate than small haloes. We detect a source of strong systematics in estimates of the triaxiality of a halo, which is found to be a strong function of the number of members; Lambda cold dark matter haloes usually characterized by triaxial shapes, slightly bent towards prolate forms, appear more oblate when taking only a small subset of the halo particles.
The ellipticities of observed 2PIGG and SDSS-DR3GC groups are found to be strongly dependent on the number of group members, so that poor groups appear more elongated than rich ones. However, this is again an artefact caused by poor statistics and not an intrinsic property of the galaxy groups, nor an effect from observational biases. We interpret these results with the aid of a GALFORM (Cole et al.) mock 2PIGG catalogue. When comparing the group ellipticities in mock and real catalogues, we find an excellent agreement between the trends of shapes with number of group members. When carefully taking into account the effects of low-number statistics, we find that more massive groups are consistent with more elongated shapes. Finally, our studies find no significant correlations between the shapes of observed 2PIGG or SDSS-DR3GC groups with the properties of galaxy members such as colour- or spectral-type index.     

Long‐slit échelle spectroscopy of galactic outflows: The case ofNGC 4449

At high redshift the ubiquity of outflows and winds in strongly star‐forming galaxies has been demonstrated using rest frame UV absorption lines. In the cases with optical emission lines, the studies mostly had to rely on low and intermediate dispersion spectra. This implies that for detailed studies of galactic wind physics we have to use local objects. In particular, dwarf galaxies are well suited to extrapolation to high redshift protogalaxies. Several kinematic studies of strongly starforming dwarf galaxies using Fabry‐Pérot and IFU spectrographs exist. Unfortunately, similar as for high redshift galaxies the employed spectral resolution is often significantly higher that the thermal line width. As a result faint high velocity features and details of the turbulent motion are hidden or unresolved. Here we will present an analysis of the ionized gas kinematics of the prototypical star‐forming irregular galaxy NGC 4449 using long‐slit, high‐dispersion échelle spectra. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structures in a class of magnetized scale-free discs

We construct analytically stationary global configurations for both aligned and logarithmic spiral coplanar magnetohydrodynamics (MHD) perturbations in an axisymmetric background MHD disc with a power-law surface mass density  Σ₀∝ r ^−α  , a coplanar azimuthal magnetic field   B ₀∝ r ^−γ  , a consistent self-gravity and a power-law rotation curve   v ₀∝ r ^−β  , where v ₀ is the linear azimuthal gas rotation speed. The barotropic equation of state  Π∝Σ ⁿ   is adopted for both MHD background equilibrium and coplanar MHD perturbations where Π is the vertically integrated pressure and n is the barotropic index. For a scale-free background MHD equilibrium, a relation exists among  α, β, γ  and n such that only one parameter (e.g. β) is independent. For a linear axisymmetric stability analysis, we provide global criteria in various parameter regimes. For non-axisymmetric aligned and logarithmic spiral cases, two branches of perturbation modes (i.e. fast and slow MHD density waves) can be derived once β is specified. To complement the magnetized singular isothermal disc analysis of Lou, we extend the analysis to a wider range of  −1/4 < β < 1/2  . As an illustrative example, we discuss specifically the  β= 1/4  case when the background magnetic field is force-free. Angular momentum conservation for coplanar MHD perturbations and other relevant aspects of our approach are discussed.