Movie 1

Movie 1 shows the evolution of the gas component of the high-resolution region of the simulation. We track the orbits of a few galaxies in order to illustrate their interaction with the cosmic web. Legends at the start of the animation identify the progenitors of three dwarfs where star formation at z=0 has largely ceased (galaxies 17, 30 and 50); the progenitor of a dwarf relatively unaffected by cosmic web stripping (galaxy 35, which is still forming stars at z=0); and the three most massive systems, which we identify with the main spiral galaxies of the Local Group: the Milky Way (MW), Andromeda (M31) and the Triangulum (M33) galaxies. The box size is indicated by the 1 Mpc-length bar (comoving) shown in the upper-right region. The orbits of the dwarfs are tracked with solid curves, from z=41 to the current position. The track colors are chosen to indicate whether the system is forming stars at z=0 at rates roughly comparable to their past average (blue) or if star formation has largely ceased (red). Galaxy 17 is at rest in the reference frame of the animation.

The evolution of the gaseous component shows the early development of highly aspherical features such as filaments and pancakes characteristic of LCDM. At z ~ 1.8 these structures gather into a large pancake-like structure (seen nearly edge-on in this projection) that sweeps past several galaxies (including galaxies 17, 30, and 50).

In order to highlight the hydrodynamical interaction with the pancake, we pause at z = 0.57 and indicate with ellipses several ``streams'' of gas that result from the ram-pressure of the moving pancake. Note that ram-pressure stripping features due to the cosmic web can be seen not only at z ~ 0.57 but also earlier, just after the pancake develops at z ~ 1.8.

The evolution of galaxy 35 provides a counterexample. As the movie shows, this galaxy forms in the central filament that joins the pancake at z ~ 1.8. Therefore, it co-moves with the pancake and is able to avoid losing most of its baryons to ram pressure. Galaxy 35 is thus able to form stars more or less continuously until z = 0.

Finally, at z ~ 0, we show the distribution of all the galaxies included in the analysis reported in this paper. MW, M31 and M33 are not labeled then for clarity. Red circles indicate the position of dwarf galaxies where star formation has largely ceased, while blue triangles indicate the position of galaxies that are still forming stars. In order to show the galaxy distribution in the context of the whole simulation, the animation zooms out in the last few seconds of the movie.

Movie 2

Movie 2 shows the evolution of the gaseous component of the simulation on a scale much smaller than Movie 1. It adopts the same projection and reference frame as Movie 1, centered on galaxy 17. Movie 2 shows in more detail an intrincate network of filaments/pancakes that collapse into a bigger one at z ~ 3. At this time, one of these structures contains several dwarf galaxies, which show as red-yellow density peaks in the movie. Note, during the assembly of each galaxy, the presence of strong feedback-driven winds leaving the galaxies. At z ~ 2, a large pancake-like structure is seen moving down at high speed (~ 300 km/s). It sweeps past all galaxies belonging to the filament that contains galaxy 17, dragging their gas in the process.

Movie 2 makes clear that the interaction between the galaxy and the cosmic web leads to the removal of a large part of the gaseous halo of galaxy 17 and several other galaxies. This gas may be seen streaming down toward the pancake at z ~ 1.4. Galaxy 17 does not lose all of its gas (some is also reaccreted later) and forms stars for a little longer before running out of cold, dense gas. (This is why the central galaxy seems to fade away at late times; recall that only the gas component is shown in this animation.) At z ~ 0.7, galaxy 17 has very little gas left and apears as a little density peak surrounded by a diffuse gaseous halo. Finally, at z > 0.5, galaxy 17 begins to accrete more gas but the density of this gas is too low for it to cool effectively and to trigger a new episode of star formation.

Movie 3

Movie 3 shows the evolution of the dark matter component in the same scale and reference frame as Movie 2. This animation shows again the intrincate network of filaments/pancakes that collapse into a bigger one at z ~ 3. Compared to the gas, the dark matter ``pancake'' is noticeably thicker, due to its collisionless nature. At z ~ 2, a large pancake-like structure is seen moving down at high speed; in contrast to the gas, which is dragged by this collision, the dark matter remains largely undisturbed. Cosmic web stripping is a purely hydrodynamical process that affects only the baryonic component of a halo.

Movie 4

Movie 4 shows the evolution of the dark matter and gas component from the same reference frame as Movie 2 (i.e., centered on galaxy 17). This movie shows the same that Movie 2 and Movie 3 but with the camera at a distance "d" from galaxy 17. It is possible to distinguish the 3D environment surrounding galaxy 17. Movie 4 makes clear that the interaction between the galaxy and the cosmic web leads to the removal of a large part of the gaseous halo of galaxy 17 and several other galaxies. This gas may be seen streaming down toward the pancake at z ~ 1.4, as the camera rotates. The change of contrast in the right-side panel was made in order to make clear the ram pressure stripping features that halo of galaxy 17 shows. Once the camera stops, the contrast becomes as before and the animation continues.