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Most Galaxy-sized systems (M_host ~ 10^12 M_sun) in the LCDM cosmology are expected to have accreted at least one satellite with a total mass M_sat ~ 10^11 M_sun = 3M_disk in the past 8 Gyr. Analytic and numerical investigations suggest that this is the most precarious type of merger for the survival of thin galactic disks because more massive accretion events are relatively rare and less massive ones preserve thin disk components. We use high-resolution, dissipationless N-body simulations to study the response of an initially-thin, fully-formed Milky-Way type stellar disk to these cosmologically common events and show that the thin disk does not survive. Regardless of orbital configuration, the impacts transform the disks into structures that are roughly three times as thick and more than twice as kinematically hot as the observed dominant thin disk component of the Milky Way. We conclude that if the Galactic thin disk is a representative case, then the presence of a stabilizing gas component is the only recourse for explaining the preponderance of disk galaxies in an LCDM universe; otherwise, the disk of the Milky Way must be uncommonly cold and thin for its luminosity, perhaps as a consequence of an unusually quiescent accretion history.
We analyze the physical properties and infall rates of the circum-galactic gas around disks obtained in multi-resolved, cosmological, AMR simulations. At intermediate and low redshifts, disks are embedded into an extended, hot, tenuous corona that co
We study the effect of dissipational gas physics on the vertical heating and thickening of disc galaxies during minor mergers. We produce a suite of minor merger simulations for Milky Way-like galaxies. This suite consists of collisionless simulation
Circumplanetary disks (CPDs) control the growth of planets, supply material for satellites to form, and provide observational signatures of young forming planets. We have carried out two dimensional hydrodynamical simulations with radiative cooling t
An observational review is provided of the properties of accretion disks around young stars. It concerns the primordial disks of intermediate- and high-mass young stellar objects in embedded and optically revealed phases. The properties were derived
We present K-band polarimetric images of several massive young stellar objects at resolutions $sim$ 0.1-0.5 arcsec. The polarization vectors around these sources are nearly centro-symmetric, indicating they are dominating the illumination of each fie