Firstly, we demonstrate that unusually large outer HI spiral arms observed in NGC 2915 can form in an extended gas disk embedded in a massive triaxial dark matter halo with slow figure rotation, through the strong gravitational torque of the rotating halo. Secondly, we show that the figure rotation of a triaxial dark matter halo can influence dynamical evolution of disk galaxies by using fully self-consistent numerical simulations. We particularly describe the formation processes of “halo-triggered” bars in thin galactic disks dominated by dark matter halos with figure rotation and discuss the origin of stellar bars in low luminosity, low surface brightness (LSB) disk galaxies. Thirdly, we provide several implications of the present numerical results in terms of triggering mechanism of starbursts in galaxies and stellar bar formation in high redshifts.

We present a three-integral orbit superposition Schwarschild model of NGC 2974, observed with the integral-field unit SAURON. We explore the dynamical structure of the stars and gas.

We present a work in progress investigating the radial distributions of dark and luminous matter in local bright spiral galaxies spanning a range of Hubble types. the distributions are derived from multiband imaging (BVRJHK) predominately from the Ohio State University Bright Spiral Galaxy Survey (OSUBSGS) and rotation curves from the literature. We use stellar colour-MIL relationships from Bell & de Jong (2001, ApJ, 550, 212) to create radial stellar mass surface density profiles for each of our galaxies. These profiles are used to create rotation curves for the stellar component; gas masses are derived from HI when available. the resulting stellar and gas mass rotation curves are compared to observed (total mass) rotation curves, and the rotation due to dark matter is determined for each galaxy. Fits to Navarro, Frenk, & White (1996, ApJ, 462, 563; NFW) halo profiles are shown. We present this analysis for 2 example galaxies from our sample of nearly 50. We will use this data to investigate correlations between these mass components and physical properties of galaxies.

The mass and distribution of baryons in galaxies is closely related to the inferred structure of the dark halo. A robust estimate of the baryon content requires knowledge of the typical mass–to–light (M/L) ratio of the stellar component. Various arguments favour a low M*/LI < 1 for late–type spirals. We show that “bottom-light” Initial Mass Functions (IMFs) favoured by recent literature do yield so low M/L ratios, for Sbc/Sc discs. We also predict the stellar M/L ratio, and hence the zero–point of the Tully–Fisher relation, to vary significantly with Hubble disc type. Finally, we provide colour–M/L relations to derive the stellar M/L ratio from the observed photometry, for different IMFs.

We use photometric, Hα and Hi data to investigate the distribution of dark matter in spiral galaxies. A new technique for deriving the Hi rotation curve is presented. the final combined Hα+Hi rotation curves are symmetric, well resolved and extend to large radii. We perform the rotation curve decomposition into the luminous and dark matter contributions. the observations are confronted with different models of the dark matter distribution, including core-dominated and cusp-dominated halos as well as less conventional possibilities. the best agreement with the observations is found for the core-dominated halos.

Relative amplitudes and pitch angles for the main two-armed spiral structure in a sample of 54 non-barred spiral galaxies were estimated from K band photometry. A lack of strong, tight patterns was observed which may be caused by non-linear dynamic effects. Assuming that the upper envelope corresponds to a relative radial forcing of ⋐5%, one can estimate the perturbation of the total potential. This suggests that a maximum disk solution is adequate to account for the force perturbation and that no additional dark matter is required.

We have performed SPH simulations for the response of the gaseous disks to the imposed potentials including those from bars and SMBHs. Evolution of the nuclear regions of gaseous disks depends critically on the masses of SMBHs as well as the sound speed in the gas.

We present new velocity dispersion measurements for a set of 12 spiral galaxies and use them to derive a more accurate υc – σ relation which holds for a wide morphological range of galaxies. Combined with the MBH – σ relation, this relation can be used as a tool to estimate supermassive black hole (SMBH) masses by means of the asymptotic circular velocity. Together with the Tully-Fisher relation, it serves as a constraint for galaxy formation and evolution models.

We present the results of a high-resolution CO-line survey using the Nobeyama Millimeter-wave Array at high-angular (⋐ 2–3″) and high spectral resolutions for the 15 CO-richest Virgo spirals. We derived exact rotation curves using position-velocity diagrams by applying the iteration method. the obtained RCs rise steeply in the central 100 pc. Surface-mass-density distributions by direct deconvolution of the RCs show massive cores of ⋐ 109M⊙ within 100 pc, suggesting the existence of DM cusps in the centres. Five galaxies were found to nest single-peaked extremely high-density molecular cores, where star formation is currently suppressed by the high differential rotation. We show that the deeper is the gravitational potential, the higher is the central gas density.

We have performed a kinematical and dynamical analysis of the ionized gas content of the late–type spiral NGC 5457 (M101) by means of scanning Fabry–Perot interferometry. the purpose of this study is to gain insight into the dark matter content in this galaxy. A sample of 263 HII regions were catalogued. We calculated radial velocity and velocity dispersions. From the dynamics of the ionized gas we were able to infer a mass of 9.8 × 1010 M⊙ inside a radius of 4'8 (or 10 kpc).

We have applied the “Synthetic Field Method” on a sample of 20 nearby galaxies in order to determine the opacity of their disks. We present preliminary results on the radial dependence of cold dust absorption for 3 examples. the spirals NGC 4535 and NGC 4725 show significant absorption at a half-light radius. UGC 2302, a LSB galaxy, shows much less opacity.

Observational data increasingly indicate that the mergers of galaxies, even minor mergers, can trigger the formation of a set of SSCs within galaxies. the follow-up, dynamical evolution of SSCs in a configuration of dark matter (DM) dominated systems would be basically similar to what we simulated in this work. the scenario that we propose yields a series of results comparable to the relevant observations. Most notable are two points. One is that the low bulge detection rate in very late-type galaxies is in favour of soft-core DM profiles in galaxies of this kind. On the other hand, the observed young ages of nuclear clusters provide evidence supporting cuspy-core profiles. in conclusion, both the soft- and cuspy-core DM density profiles are suitable to relevant dwarf galaxies based on comparisons with observations.

We present results obtained from a study of the mass distribution of 24 galaxies observed using Fabry-Pérot techniques, as part of the GHASP survey (see Russeil et al., this meeting). For each galaxy, we combined high resolution Hα rotation curves derived from 2-D velocity fields, with low resolution HI data, in order to determine accurately the inner slope of the rotation curve which strongly constrains the distribution of matter. Our work suggests the existence of a constant density core in the center of the dark halos.

I will present a new method of dynamical modeling of stellar systems based on evolutionary algorithms. the technique will be illustrated with an application to the problem of recovering the gravitational potential of a thin galactic disc from kinematic observables in a non-parametric way.

We present Hα emission line velocity fields of two Low Surface Brightness galaxies (LSBs) - UGC 628 and UGC 5005 - obtained using Fabry-Perot (FP) interferometry observations at the Canada-France-Hawaii telescope. Our goal is to study the dynamics of LSBs.

We use optical, long-slit rotation curves to derive the slope of the central density profile in three blue disk galaxies with very faint central surface brightness values. We find the result to be in conflict with current cold dark matter predictions and to lend further support for pseudo-isothermal spheres as superior models for the dark halos of galaxies.

We present preliminary results from spectroscopic observations of a sample of 11 low surface brightness galaxies (LSB). We measured the stellar and gaseous kinematics along their major and minor axes. Such information will allow us to accurately investigate the dark matter (DM) content within their optical regions, providing further constraints on the predictions of standard CDM models. Although dynamical modeling is still in progress, our observations already show that the derived stellar kinematics is more regular than the ionized gas one, which often shows evidence for non-circular and asymmetric motions.

We investigate the relation between the central velocity dispersion, σc, and the circular velocity, Vcirc, in galaxies. in addition to previously obtained data, we consider an observationally homogeneus sample of 52 high surface brightness and 11 low surface brightness spiral galaxies. We performed a straight line regression analysis in a linear scale, finding a good fit, also for low σc galaxies, always rejected in the previous studies. Low surface brightness galaxies seem to behave differently, showing either higher values of Vcirc or lower values of σc with respect to their high surface brightness counterparts.

The varying dwarf galaxy populations in different environments pose a problem for Cold Dark Matter (CDM) hierarchical clustering models. in this paper we present results from a survey conducted in different environments to search for low surface brightness (LSB) dwarf galaxies.

Using detailed Monte Carlo radiative transfer modeling, we examine the effects of absorption and scattering by interstellar dust on the observed kinematics of galaxies. Our modeling results have a direct impact on the derivation of the properties of dark matter haloes around both elliptical and spiral galaxies. We find that interstellar dust has a very significant effect on the observed stellar kinematics of elliptical galaxies, in the way that it mimics the presence of a dark matter halo. Taking dust into account in kinematical modeling procedures can reduce or even eliminate the need for dark matter at a few effective radii. Dust profoundly affects the optical rotation curve and stellar kinematics of edge-on disc galaxies. This effect, however, is significantly reduced when the galaxy is more than a few degrees from strictly edge-on. These results demonstrate that dust attenuation cannot be invoked as a possible mechanism to reconcile the discrepancies between the observed shallow slopes of LSB galaxy rotation curves and the dark matter cusps found in CDM cosmological simulations.