Behavior of luminous matter in the head-on encounter of two ultralight BEC dark matter halos

Within the context of ultralight Bose-Einstein condensate (BEC) dark matter, we analyze the head-on encounters of two structures. These structures are made of a BEC component, which is a ground-state equilibrium solution of the Gross-Pitaevskii-Poisson (GPP) system, together with a component of luminous matter. The evolution of the condensate dark matter is carried out by solving the time-dependent GPP equations, whereas the luminous matter is modeled with particles interacting gravitationally on top of the BEC dark matter halos. We track the evolution of frontal encounters for various values of the collision velocity and analyze the high-velocity regime showing solitonic behavior of the BEC halos and that of slow velocities producing a single final structure. We measure the relative velocity of the dark matter with respect to the luminous matter after the encounters in the solitonic case and track the evolution of luminous matter in the case of merger.

Figure 1

We show three snapshots of the distribution of luminous particles and isocurves of ${\rho }_{\mathrm{BEC}}$ at $t=0$, 20, 40 in code units. The luminous particles by construction have peculiar motion around the center of mass; however the density profile remains localized. In the bottom right we also show the position of the maximum of ${\rho }_L$ in the $xz$ plane in time, which shows the box size where the maximum of ${\rho }_L$ is changing.

Figure 2

We show four snapshots of ${\rho }_{\mathrm{BEC}}$, ${\rho }_L$ and $\mathrm{Re}(\mathrm{\Psi })$ at various times for a boosted configuration. The density profiles of each component remain nearly time independent as expected. The initial momentum added to the configuration is $v_z=1.5$, which is the highest we use in the paper. In the bottom panel we show the location of the maxima of both components and the difference between them along the $z$ axis, which is the direction of the boost.

Figure 3

We show snapshots of ${\rho }_{\mathrm{BEC}}$, ${\rho }_L$ and $\mathrm{Re}(\mathrm{\Psi })$ at various times for a collision with $v_z=1$. In the bottom panel we show the trajectory of the maximum of each blob for dark and luminous matter. We use 5000 particles for the luminous matter.

Figure 4

Values of $d_A$ for $v_z=1$ and $v_z=1.5$ respectively. We have removed the time window where the interference pattern occurs and the maximum of ${\rho }_{\mathrm{BEC}}$ is located basically at the origin.

Figure 5

We show the fits of the relative motion between ${\rho }_{\mathrm{BEC}}$ and ${\rho }_L$ for various values of $v_z>0.755$ after the collision.

Figure 6

We show snapshots of ${\rho }_{\mathrm{BEC}}$, ${\rho }_L$ and $\mathrm{Re}(\mathrm{\Psi })$ at various times for a collision with $v_z=0.5$ in code units. We use 5000 particles for the luminous matter.

Figure 7

Snapshots of the evolution of the luminous matter and contours of ${\rho }_{\mathrm{BEC}}$ that show their relative locations for $v_z=0.2$. As the dark matter gets glued during the collision, the luminous matter becomes diluted.

Figure 8

We show the central values of ${\rho }_{\mathrm{BEC}}$ and $V$ in time, in code units, for the simulation in Fig. 7.