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recent hst proper motion measurements of the magellanic clouds by kallivayalil et al .
( 20006a , b ) and @xcite indicate that they are presently moving at velocities substantially higher ( almost 100 km s@xmath1 ) than those provided by previous observational studies ( van der marel et al .
2002 , kroupa & bastian 1997 ) .
such high velocities ( @xmath2 km s@xmath1 and @xmath3 km s@xmath1 for the lmc and smc , respectively ) are close to the escape velocity of the milky way and consistent with the hypothesis of a first passage about the galaxy ( besla et al . 2007 ) .
a single perigalactic passage has serious implications for the origin of the magellanic stream .
it definitely rules out the tidal stripping hypothesis ( ruzicka , theis & palous 2008 ) since in this scenario the loss of mass is primarily induced by tidal shocks suffered by satellites at the pericenters ( mayer et al .
2006 ) and the stream would not have time to form before the present time .
indeed kinematical data suggest that the clouds are now just after a perigalactic passage . on the other hand , ram - pressure scales as @xmath4 , where @xmath5 is the relative velocity between satellites and the ambient medium .
the high velocities of the clouds could therefore compensate the effect of the reduced interaction time with the hot halo of the mw and hydrodynamical forces would play a determinant role in forming the stream .
+ in @xcite ( hereafter m05 ) we have performed high resolution n - body / sph simulations to study the hydrodynamical and gravitational interaction between the lmc and the mw using orbital constraints by @xcite and a present time satellite velocity of 250 km s@xmath1 .
we found that , after two perigalactic passages , the combined effect of tidal forces and ram - pressure stripping can account for the majority of the lmc s internal features and for the formation of the ms .
more in detail , ram - pressure stripping of cold gas from the lmc s disk produces a stream with morphology and kinematics similar to the observed ones , while tidal stripping has longer time - scales and is not efficient in forming stellar debris , consistently with the lack of stars observed in the stream .
nevertheless , at each pericentric passage the lmc suffers tidal heating which perturbs the overall structure of the satellite reducing the gravitational restoring force and therefore indirectly contributing to the loss of gas .
+ the main objection to this model , in light of the new proper motion measurements of the lmc , is that the time spent by the lmc within the hot halo of the mw would be to short to cover the full extension of the stream ( more than 100 degree ) by ram - pressure mechanisms ( besla et al .
moreover , hydrodynamical forces would affect a galaxy only weakly perturbed by the gravitational interaction and stripping would result more difficult .    in this work i present the results of n - body / sph simulations where the interaction between the mw and the lmc is modeled according to the new proper motion measurements of @xcite .
the initial condition of the simulations are constructed using the technique described by @xcite .
both the mw and the lmc are multi - component galaxy models with a stellar and gaseous disk embedded in a spherical dark matter halo .
the density profile of the nfw halo is adiabatically contracted due to baryonic cooling .
stars and cold gas in the disks follow the same exponential surface density profile .
we also explore the eventuality of an extended lmc gaseous disk . in this model
the gaseous disk is characterized by an additional constant density layer which extends up to eight times the scale length of the exponential disk .
the mw model comprises also a small stellar bulge and an extended low density ( @xmath6 @xmath7 within 150 kpc from the galactic center and @xmath8 @xmath7 at 50 kpc ) hot ( @xmath9 k ) halo in hydrostatic equilibrium inside the galactic potential ( m05 ) .
the mw model , with virial mass @xmath10 and concentration @xmath11 , is similar to model a1 of @xcite while the structural parameters of the lmc are chosen in such a way that the resulting rotation curve resemble that of a typical bulgeless late - type disk galaxy . in details , the satellite has virial mass @xmath12 , concentration @xmath13 and the same amount of mass in the stellar and gaseous disk component ( @xmath14 ) .
the toomre s stability criterion is always satisfied and the parameter @xmath15 set equal to 1.5 and 2.0 at the disk scale radius in the different lmc models .
i performed adiabatic simulations using gasoline , a parallel tree - code with multi - stepping ( wadsley et al .
high resolution runs have @xmath16 particles , of which @xmath17 are used for the disks and @xmath18 for the hot halo of the mw .
the gravitational spline softening is set equal to 0.5 kpc for the dark and gaseous halos , and to 0.1 kpc for stars and gas in the disk and bulge components .        in my best model
the lmc approaches the mw on an unbound orbit ( fig .
[ orbit ] ) with initial galactocentric distance of 400 kpc and velocity @xmath19 km s@xmath1 .
after the perigalactic passage ( at @xmath20 kpc ) the velocity decreases faster than for a ballistic orbit as a result of dynamical friction .
the escape velocity at a given lmc position is indicated by a red curve in the right panel and calculated assuming a spherical unperturbed host potential . due to the effects of dynamical friction , at late times
the satellite lies on a nearly parabolic orbit . at the present time
( @xmath21 gyr , vertical lines in the plots ) it reaches a velocity of @xmath22 km @xmath23 at @xmath24 kpc from the galactic center , in good agreement with the new proper motion measurements . + in choosing the initial inclination of the lmc i made the approximation that it does not change during the interaction due to the effects precession or nutation of the disk plane . at the beginning of the simulation
the disk moves almost face - on through the external medium , and ram - pressure affecting the whole disk perpendicularly . in proximity to the perigalactic passage the velocity vector changes rapidly and
the angle between the satellite s disk and the proper motion is close to zero . at the present time the simulated disk has an inclination of about 30 degree with respect to the orbital motion ( kallivayalil et al .
2006a ) and is indeed moving nearly edge - on through the external hot gas , with ram - pressure compressing its eastern side .
[ aitoff ] illustrates the present time distribution of stars and gas originating from the lmc s disk .
the stellar disk becomes elongated while tidal debris start forming after the perigalactic passage .
but all stars stay bound to the satellite .
tidal heating does not perturb significantly the vertical structure of the disk that remains thin and does not create a warp , unlike what observed in m05 .
bar instability develops at the perigalacticon only in the case of @xmath25 . + ram - pressure strips nearly @xmath26 of gas from the lmc s disk forming a continuous stream that lies in a thin plane perpendicular to the disk of the mw and extending up to @xmath27 degrees from the lmc ( fig .
[ aitoffcirc ] ) .
the location of the stream in the southern galactic hemisphere is comparable to the values of @xmath28 and @xmath29 provided by observations .
contrary to m05 there is no lmc s gas above the galactic plane . in m05
the material lying in the northern hemisphere is stripped from the satellite during the orbital period preceding the present one and the stream forms a great polar circle around the galaxy . the lack of gas at @xmath30 in fig .
[ aitoffcirc ] is not due to inefficient ram - pressure at early times , but to the fact that , in order to reproduce the current location and velocity of the lmc , the satellite enters the mw halo exactly at @xmath31 .
the morphology of the stream does not change significantly adopting an extended gaseous disk model ( top panel of fig .
[ aitoffcirc ] ) , except for the region at the head of the stream , which appears broader ( bottom ) .
i carried out high resolution gravitational / hydrodynamical simulations of the interaction between the lmc and the mw using the orbital parameters suggested by the new hst proper motion measurements .
i find that ram - pressure stripping exerted by a tenuous mw hot halo during a single perigalactic passage forms a stream whose extension and location in the sky are comparable to the observed ones .
the stellar structure of the satellite is only marginally affected by tidal forces .
+ the numerical simulations were performed on the l sgi - altix 3700 bx2 at the university observatory in munich .
this work was partly supported by the dfg sonderforschungsbereich 375 `` astro - teilchenphysik '' .
i use high resolution n - body / sph simulations to model the new proper motion of the large magellanic cloud ( lmc ) within the milky way ( mw ) halo and investigate the effects of gravitational and hydrodynamical forces on the formation of the magellanic stream ( ms ) . 
 both the lmc and the mw are fully self consistent galaxy models embedded in extended cuspy @xmath0cdm dark matter halos . 
 + i find that ram - pressure from a low density ionized halo is sufficient to remove a large amount of gas from the lmc s disk forming a trailing stream that extends more than 120 degrees from the cloud . 
 tidal forces elongate the satellite s disk but do not affect its vertical structure . 
 no stars become unbound showing that tidal stripping is almost effectiveless .