Published Article: Identifying supermassive black hole recoil in elliptical galaxies
Our article explores the effect an SMBH ejected from the centre of the galaxy through a gravitational wave-induced kick after coalescence has on the surrounding stellar medium. We tackle the problem from both the effect the recoiling SMBH has on the mass density profile of the galaxy, and from the perspective of a change in stellar kinematic structure. We’re able to infer the recoil velocity of a SMBH given the projected mass density of the galaxy and the excess of non angular momentum-conserving orbits in the central regions of the galaxy. We predict that in general, the recoil velocities of coalescing SMBHs is relatively low in massive elliptical galaxies.
Abstract:
We study stellar core growth in simulations of merging massive \((M_\star > 10^{11}\,\mathrm{M}_\odot)\) elliptical galaxies by a supermassive black
hole (SMBH) displaced by gravitational wave induced recoil velocity.
With controlled, dense sampling of the SMBH recoil velocity, we find the core radius originally formed by SMBH binary scouring can grow by a factor of 2-3 when the recoil
velocity exceeds \(\sim50\) per cent of the central escape velocity, and the mass deficit grows by up to a factor of \(\sim 4\).
Using Bayesian inference we predict the distribution of stellar core sizes formed through this process to peak at \(\sim 1\,\mathrm{kpc}\).
An orbital decomposition of stellar particles within the core reveals that radial orbits dominate over tube orbits when the recoil velocity exceeds the velocity dispersion of the core,whereas tube orbits dominate for the lowest recoil kicks.
A change in orbital structure is reflected in the anisotropy parameter, with a central tangential bias present only for recoil velocities less than the local stellar velocity dispersion.
Emulating current integral field unit observations of the stellar line-of-sight velocity distribution, we uncover a distinct signature in the Gauss-Hermite symmetric deviation coefficient \(h_4\) that uniquely constrains the core size due to binary scouring.
This signature is insensitive to the later evolution of the stellar mass distribution due to SMBH recoil.
Our results provide a novel method to estimate the SMBH recoil magnitude from observations of local elliptical galaxies,and implies these galaxies primarily experienced recoil velocities less than the stellar velocity dispersion of the core.