3D Moving-mesh Hydrodynamical Simulations of Wind/Jet Driven Ultraluminous X-ray Source Bubbles

TL;DR

This study addresses how disk winds from ultraluminous X-ray sources inflate large-scale bubbles by performing 3D moving-mesh hydrodynamic simulations with AREPO and injecting winds inside a cone of half-opening angle $\alpha$ with velocity $v_0$ and mechanical power $L_{\rm mec}$. Results show morphology is largely controlled by the initial wind momentum (and recollimation), while $L_{\rm mec}$ mainly sets bubble size; low $L_{\rm mec}$ can lead to rapid shell cooling and collapse, and jet bubbles display stronger recollimation and a persistent cold jet core. Comparison with observations of NGC 55 ULX-1 and NGC 1313 X-2 favors narrow funnel outflows and demonstrates that emission-measure profiles can help break degeneracies between geometry and viewing angle, improving constraints on ULX accretion-disk winds.

Abstract

We perform 3 dimensional moving-mesh hydrodynamical simulations of bubble nebulae around ultraluminous X-ray sources, using state-of-the-art software AREPO. We use a Monte-Carlo method to inject outflows with uniform mass outflow rate and momentum, in a conical funnel with a specific half opening angle. Simulation results show that the morphology of the bubble is determined by the initial momentum of the outflows, while the mechanical power of the outflows only influences the size of the bubble without changing its shape. Low mechanical power also results in a short cooling timescale of the system, leading to an early collapse of the bubble shell. The half opening angle of the outflows and the viewing angle of the system determine the observed bubble eccentricity together. Compared with the observational morphology of the ULX bubble sources NGC 55 ULX-1 and NGC 1313 X-2, our simulation favors the fact that the high velocity outflows of the accretion disks in these two systems are confined in a narrow funnel region.

Figures (11)

• Figure 1: Slice plots of the two hyper-refined injection regions on the plane that cuts through the north and south poles of the central black hole. The left panel shows the Voronoi mesh of the inner 20 pc of the simulation domain. The right panel shows the Voronoi mesh of the inner 5 pc. The red circles show the projections of the injection regions on the plane.
• Figure 2: Azimuthally averaged snapshots of the bubbles produced by the $45^{\circ}$ wide-angle disk winds. The left panels show the number density color maps overlaid with velocity streamlines, where the thickness of the streamlines represents the magnitude. The middle column panels and the right column panels show the color maps of the radial velocity and the gas temperature, respectively. From the top to the bottom row, the data come from the runs WIND-FID, WIND-LOWV, WIND-LOWL, and WIND-LOWN, respectively. All the snapshots are taken at $t=280$ kyr, except for the run WIND-LOWN, where the snapshot is taken at $t=125$ kyr.
• Figure 3: Radial profiles of number density $n$, radial velocity $v_r$, Mach number $\mathcal{M}$, gas temperature $T$, gas pressure $p_{\rm gas}$, and ram pressure $p_{\rm ram}$ of the runs WIND-FID, WIND-LOWV, and WIND-LOWN, respectively. All the radial profiles are taken from the same snapshots of Figure \ref{['fig:wind_bubble']}. The data is azimuthally and pitch angle averaged between $\theta=0^{\circ}$ and $\theta=10^{\circ}$.
• Figure 4: Azimuthally averaged $\theta$ direction profiles of number density $n$, radial velocity $v_r$, transverse velocity $v_{\theta}$, and gas temperature $T$ of the runs WIND-FID, WIND-LOWV, and WIND-LOWN, respectively. All the transverse profiles are taken from the same snapshots of Figure \ref{['fig:wind_bubble']} and at $r=50$ pc from the central black hole.
• Figure 5: Azimuthally averaged snapshots of the bubbles produced by the $5^{\circ}$ narrow-angle jets. The left panels show the number density color maps overlaid with velocity streamlines, where the thickness of the streamlines represents the magnitude. The middle column panels and the right column panels show the color maps of the radial velocity and the gas temperature, respectively. From the top to the bottom row, the data come from the runs JET-FID, JET-LOWV, JET-LOWL, and JET-LOWN, respectively. The snapshots of JET-FID and JET-LOWL are taken at $t=150$ kyr. The snapshots of the runs JET-LOWV and JET-LOWN are taken at $t=73$ kyr and $t=45$ kyr, respectively, when the shock front is at the same distance as that of JET-FID.