We use analytical arguments and N-Body/SPH simulations to show that the presence of an effective temperature floor of ~10⁴K naturally explains the tendency for small galaxies to be more spheroidal, more gas rich, and less efficient in converting baryons into stars than larger galaxies. While unimportant for galaxies within large dark matter halos, a reasonable temperature floor produces a pressure support radius that is comparable to the angular momentum support radius in halos with low virial temperatures. The effect becomes important in galaxies with circular velocities smaller than ~100 km/s and becomes increasingly significant in dwarf galaxies (~40 km/s). Though quite simple, this intuitive mechanism explains many of the observed trends seen in small galaxies. We suggest that most dwarf systems do not start off as thin disks, but rather are born as thick, mildly rotating systems.

The NFW halo has been difficult to reconcile with low surface brightness (LSB) galaxy data. NFW fits to LSB rotation curves often have concentrations lower than expected for a LCDM cosmology, and high-resolution Hα velocity fields do not show the characteristic NFW pinching of isovelocity contours. We simulate the two-dimensional NFW halo and test several modifications to the potential in an attempt to simultaneously reconcile both the NFW velocity field and rotation curve with observed LSB galaxy data. We present mock velocity fields and rotation curves of axisymmetric and non-axisymmetric NFW potentials and compare our simulation results to high-resolution velocity fields from integral field spectroscopy of LSB galaxies.

Major and minor axis stellar and ionized gas kinematics of a sample of bulge dominated low surface brightness galaxies is presented. The stellar kinematics, together with broad band imaging, is used to construct detailed mass models aimed at deriving the central density radial profile of the dark matter component. For the two sample galaxies that have been so far modeled, we find that a flat-density core dark matter halo is preferred. Moreover the ionized gas kinematics is not consistent with the model potential, suggesting that it is not a reliable tracer of the mass distribution in the central region.

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I will describe the results of state-of-the art cosmological hydrodynamical simulations following the formation of a Milky Way-sized disk galaxy. I will address how the formation of the disk depends on numerical resolution and feedback processes such as heating and winds from supernovae explosions as well as the cosmic ultraviolet background. I will show that the angular momentum catastrophe is avoided once a resolution of millions of particles is achieved in the galaxy. A realistic rotation curve is obtained and the resulting galaxy matches the Tully Fisher relation reasonably well. I will also discuss the populations of satellites formed in the simulation, showing how these are still difficult to resolve properly. I will then contrast these results with those of a novel simulation following the formation of a galaxy with much lower mass, similar to M33 in our Local Group, addressing the following fundamental question: is it possible to form a bulgeless disk galaxy in a CDM Universe?

LCDM numerical simulations predict that the “missing baryons” reside in a Warm-Hot gas phase in the overdense cosmic filaments. There are now several theoretical and observational arguments like the presence of star formation in the outskirts of galaxies, the improvement of the baryonic Tully-Fisher relation or the detection of a dark component in the tidal dwarf galaxies that support the fact that galactic disks may be more massive than usually thought, containing a substantial fraction of the “missing baryons”. We will present N-body simulations of galactic disks, where the gas content has been multiplied by a factor between 2 and 5. The stability of the disk is ensured by assuming that the ISM is composed out of two partially coupled phases, a warm phase, corresponding the observed CO and HI gas and a cold (but dynamically warm) phase corresponding to the unseen baryons. Amongst other results we will show that this model reproduces well the amount of dark matter observed in tidal dwarf galaxies.

We use a disk galaxy evolution model to investigate the origin of exponential density profiles of disk galaxies and the evolution of the Tully-Fisher and Size-Luminosity Relations. Our model follows the detailed accretion, cooling, and ejection of baryonic mass inside growing dark matter haloes. In our model the surface density profile of the disk is determined by detailed angular momentum conservation, starting from the distribution of specific angular momentum as found in cosmological simulations. Through a combination of star formation and feedback we are able to produce a sample of galaxies with close to exponential surface density profiles. We constrain the free parameters of this model using the local Tully-Fisher and Size-Luminosity relations. Then we investigate the evolution of the Tully-Fisher and Size-Luminosity relations and compare the model predictions with recent observations.