Many galaxies at high redshift have peculiar morphologies dominated by 10⁸-10⁹ M(sun) kpc-sized clumps. They appear as “chain galaxies” (Cowie et al. 1996) when observed edge-on, otherwise as “clump-cluster galaxies” (Elmegreen et al. 2004). Using numerical simulations, we show that these chains and clump-clusters result from fragmentation in gravitationally unstable primordial disks, and we study their evolution. In less than 1 Gyr, clump formation, migration, disruption, and interaction cause these systems to evolve from initially irregular and bulgeless disks into regular spiral galaxies with an exponential or double-exponential disk profile, and a central bulge formed at the same time. A nuclear black hole may also form simultaneously from smaller black holes that grow inside the dense cores of each clump. The properties and lifetimes of the clumps in our models are consistent with observations, in particular the lack of organized rotation in chain galaxies. We suggest that violently unstable disks are an early fundamental step in the formation of spiral galaxies at z=1 and above, which further evolve secularly at lower redshift. The associated starburst activity is intense, and gives a short timescale for the initial stellar disk to form. (Bournaud et al. 2007).

We look at cold flows and shocked gas in SPH cosmological simulations, and determine their relationship to angular momentum. Does shocked gas cool into the disk? We know that dark matter halos have broad distribution of angular momentum, which includes low and negative values. Can baryons with initially negative angular momentum end up in the disk? What path through density-temperature phase diagrams is taken by disk baryons? Our analysis provides new insights into disk galaxy formation within the context of cold dark matter hierarchical buildup.

In order to verify the correlation between the disk circular velocity Vc and the central velocity dispersion of the spheroidal component ?c, we analyzed a sample of 12 low surface-brightness (LSB) galaxies. In previous works LSB galaxies have been claimed to follow either a different linear (Pizzella et al. 2005) or the same power-law relation (Buyle et al. 2006) with respect to high surface brightness (HSB) galaxies. The galaxies studied in this work enable us to confirm that LSB galaxies and HSB galaxies follow two different linear Vc-?c relations.

We want to study the bulge and the disk kinematics of the giant low surface brightness (LSB) galaxy ESO323-G064 in order to investigate is dynamical properties and the mass radial profile of the dark matter (DM) halo. We observed the galaxy with the integral field spectroscopy (VLT/VIMOS, in IFU configuration) measuring the ionized gas (fitting Gaussian functions to the [OIII] and H? emission lines) and stellar (fitting stellar template to the galaxy spectrum) velocity and velocity dispersion fields. The stellar kinematics has been modelled with a spherical isotropic Jeans models, exploring the self consistent and the dark matter scenarios (NFW and pseudo isothermal halo). The lack of good photometry and the limited radial extension of the stellar kinematics did not allow us to extend the models to the disk component and to consider more complicated scenarios (i.e. anisotropy, bars). The bulge-dominated region (R<5”) is characterized by and a very complex ionized gas kinematics, and the emission lines show a multi peaked profile. The disk dominated region (15”

I will outline our semi-analytical model for the formation of galaxies: The high-redshift domain is thought to be where the core of the dark matter potential is built up due to the high frequency of mergers, the formation of disk-structures is suppressed in this epoch and the baryonic matter collapses whilst losing its angular momentum to the dark matter particles to form a spheroid structure, also promoting the growth of a supermassive black hole. Secondly, this dissipative collapse sequence is thought to increase the kinetic energy of the dark matter particles and therefore modify the DM halo density profile. However, in the relatively quiescent lower redshift Universe, disks may form around the pre-existing spheroid components due to an accretion of matter with a dissipationless collapse. We therefore analyse the build up of disk structure in the domain z<2-3 within pre-processed halos using the semi-analytic method and track the structural and dynamical evolution of disk structure.

We report on preliminary results of high-resolution simulations of disk galaxy formation in a fully cosmological environment using a new prescription for feedback implemented in the N-body/SPH code GADGET2. It has turned out that the emergence of large gaseous disks with high angular momentum is rather elusive using standard prescriptions for star formation and stellar feedback. We will discuss the processes by which gas loses its angular momentum during the protogalactic collapse phase, leading to disk galaxies that are too compact with respect to the observations and we show which conditions lead to a gaseous disk and discuss the angular momentum conservation.

An explanation for the shapes and features of disk galaxy density profiles, as well as their temporal evolution, is currently lacking. In an attempt to address this situation, we have conducted one of the largest sets of galaxy simulations to date using the N-body/SPH code Gadget-2 on the Canadian high performance computing network SHARCNET. We create galaxies on the basis of halo concentration, mass and spin, as well as disk mass fraction and a possible bulge. A grid search of galaxy parameters consisting of 200 simulations and totaling more than 590,000 CPU hours was performed to examine the relative importance of dynamical parameters on the development of the radial density profiles and the subsequent secular evolution of these profiles. We find that the evolution of the galaxy mass density profiles is controlled by the ratio of the disk mass fraction to the halo spin parameter. The strength of a two-component structure in disk profiles and the speed at which this structure develops, is directly proportional to md/?. We find that the outer density profile is in close agreement with the initial density profile and remains stable over time, whereas the inner profile slope evolves considerably. We pay close attention to those simulations whose density profiles remain exponential over time.

In the past few years we have developed a rather new scenario for the joint formation of spheroids and SMBH, which has proved to be remarkably successful in explaining several observations at low and high redshift related to these systems. The tests have been done with SAM technique. Now we have complemented this model with a scheme for the formation of disks, according to which the observed dichotomy between disks and spheroids has an origin (usually) different from the merging driven one adopted by standard SAM models.

NGC4650A is considered the prototype of the class of wide Polar Ring Galaxies (PRGs): this is a peculiar object composed by a central spheroidal component, the host galaxy, and an extended disk made up by gas, stars and dust, which orbits nearly perpendicular to the plane of the central galaxy (Iodice et al. 2002, Gallagher et al. 2002). This object is one of the best-investigated PRGs, and therefore presents an excellent opportunity for constraining the 3D shape of its dark matter halo. We present the analysis of the dark matter halo content and shape along two perpendicular directions (the equatorial and the meridian planes). We use the stellar kinematics of the spheroid along the equatorial direction and the combined information of stars and gas along the meridian axis. The convergence of high quality kinematical data from different tracers allows us to have unprecedented constraints on the dark matter 3D distribution to be compared with predictions from cosmological simulations (Navarro et al. 1996, 1997, Bullock et al. 2001).

We have investigated the structure and kinematics of the dwarf galaxies DDO47 and NGC3741. They are gas-rich and possess extended HI disks, hence permitting to probe the gravitational potentials out to large radii. The derived rotation curves have a spatial resolution of 200-300 pc. They have been corrected for non-circular motions via modelling of the data cube and a harmonic decomposition of the velocity field. The derived rotation curves are best fitted by cored dark matter halos, while NFW profiles do not comply with them. The derived non-circular motions in DDO47 are not sufficient top hide a CDM cusp. We have also started to study the three-dimensional structure of dwarf galaxies with prodigious gaseous disks. The HI disk of NGC3741 extends out to 42 (B-band, stellar exponential) scale-lengths. Likewise, DDO154 has a huge warped HI disk, however with a highly asymmetric three-dimensional structure. We discuss possibly implications.

Predictions for dark matter halo morphology come from N-body simulations and are generally based on fitting ellipsoids to the density distribution. This has partly been dictated by the low mass resolution of past simulations. However the current state-of-the-art simulations involve halos with several million particles and produce halos with more complicated shapes than perfect ellipses i.e. boxy, disky, or deviations of still higher order. In order to characterize these deviations in three dimensions, we measure the shapes of halos as higher order spherical harmonic deviations from ellipsoids, extending the two dimensional analogue to our high resolution simulations. Observations find that deviations from ellipticity correlate with the kinematic state of elliptical galaxies. Thus we attempt to reproduce such measurements in a three-dimensional context to determine if the deviations from ellipsoids correlate with the degree of rotation and to explore how the shapes change in the presence of disks. As growth of disks inside halos has been shown to lead to reversible shape change (Debattista et al. submitted), we anticipate similar shape changes in the higher order moments of the same simulations.

We performed cosmological simulations of disks with different mass e gas fractions and the star formation switched on. Such disks evolved along 10 Gyr inside the same cosmological dark matter halo where they are embedded at high redshift (z=2). Pure stellar disks develop bars living up to z=0 (Curir et al. 2006). The inclusion of a different gas fraction, from 0.1 to 0.6 of the disk mass, does not succeed in the bar destruction in DM dominated disks. However, in more massive disks, a gas fraction of 0.2 is able to destroy the bar starting from z=0.5 (Curir et al. 2007). We found that the fully cosmological framework plays a crucial role in the evolution of the whole system when more massive disks are considered. In Such a case, indeed, the bar cannot destroy the halo triaxiality which always restores its initial value, also when the bar is destroyed. Here we aim at going deeply into these points including the effects of the star formation which fuels the bar instability, as suggested by our previous studies (Mazzei & Curir 2001).

We investigate the basic properties of local HI-rich galaxies by using semi-analytic galaxy formation models, taking into account the merging processes of dark halos, based on the hierarchical structure formation scenario. The local HI-rich galaxies detected in blind radio surveys provide us with important clues to revealing the formation and evolution processes of galactic disks. By making a comparison with the observational results of the blind radio surveys (e.g., the Arecibo Dual-Beam Survey and the HI Parkes All Sky Survey) and the surveys for the optical counterparts (e.g., the Survey for Ionization in Neutral Gas Galaxies), we find the following points; (1) the cross-sections of the galactic HI disks (the HI column density > 10^{19} cm^{-2}) correlate tightly with the HI masses; sigma \propto M_{HI}^{p} with p=0.92-0.99 in the range of HI mass from 10^{6} to 10^{10.5} M_sun, (2) The cross sections of the HI disks reach up to 10^{4} [kpc^{2}] for the massive galaxies with the HI mass M(HI)=10^{11} M_sun, and (3) the star formation rates (SFR) correlate strongly with the HI masses; SFR \propto M_{HI}^{x} with x=1.3-1.4 in the range of HI mass from 10^{6} to 10^{11} M_sun. We also discuss a link between the HI-selected galaxies and the quasar absorption systems (DLA and sub-DLA systems) originating in HI gas of galaxies.

We explore the possibility that extended disks, such as that recently discovered in M31, are the result of a single dwarf (10⁹-10¹⁰ M(sun)) satellite merger. We carry out self-consistent N-body simulations of dwarf NFW halos with embedded spheroidal stellar components on prograde orbits in a live M31-like host galaxy. As the orbit decays due to dynamical friction and the system is disrupted, the stellar particles form an extended, exponential disk-like structure that spans the radial range 30-200 kpc once they have relaxed. The disk scale-length correlates with the initial extent of the stellar component within the satellite halo: the more embedded the stars, the smaller the resulting disk scale-length. If the progenitors start on circular orbits, the kinematics of the stars that make up the extended disk have an average rotational motion that is 30--50 km/s lower than the host's circular velocity. For dwarf galaxies moving on highly eccentric orbits (e=0.7), the stellar debris exhibits a much lower rotational velocity. Our results imply that extended galactic disks might be a generic feature of the hierarchical formation of spiral galaxies such as M31 and the Milky Way.

We have explored the galaxy disk/extended halo gas kinematic relationship using rotation curves (Keck/ESI) of ten intermediate redshift galaxies which were selected by MgII halo gas absorption observed in quasar spectra (Keck/HIRES, VLT/UVES). The halo gas is sampled at projected galactocentric distances of 25-105 kpc and at a range of position angles with respect to the galaxy major axis. Previous results of six edge-on galaxies, probed along their major axis, suggest that observed halo gas velocities are consistent with the galaxy disk angular momentum; implying extended disk-like halo rotation at galactocentric distances of 25-72 kpc. Using our new sample of ten galaxies, we demonstrate that the gas velocities are by and large not consistent with being directly coupled to the galaxy kinematics. Our sample contains two pairs of interacting galaxies and in one case, the gas velocities are both retrograde to the disk rotations and the angular momentum of the system. Thus, mechanisms other than co-rotation dynamics (i.e., gas inflow, feedback, galaxy-galaxy interactions, etc.) must be invoked toaccount for the overall observed kinematics of the halo gas. In order to better understand the dynamic interaction of the galaxy/halo/cosmic web environment, we performed similar mock observations of galaxies and gaseous halos in Lambda-CDM cosmological N-body simulations, with resolutions of 20-50 parsecs. Physical processes influencing halo gas dynamics, such as radiative cooling, star formation, metal enrichment, and thermal feedback due to supernovae, are implemented in the code. We present an example case of a z=0.85 galaxy with various orientations probing halo gas at a range of positions. The gas dynamics inferred using simulated quasar absorption lines are also inconsistent with observational data. Our results suggest that the galactic inflow and outflow mechanisms currently implemented in cosmological models are not yet fully understood.