Published Article: The supermassive black hole merger-driven evolution of high-redshift red nuggets into present-day cored early-type galaxies
In this article, we use N-body simulations run with the KETJU code to study the evolution of high-redshift compact galaxies into present-day early-type galaxies, which contain low-density cores. The simulations demonstrate that the presence of supermassive black holes is crucial for the merger-driven evolution of high-redshift red nuggets into the local elliptical galaxy population.
Abstract: Very compact (\(R_\mathrm{e}\lesssim 1\) kpc) massive quiescent galaxies (red nuggets) are more abundant in the high-redshift Universe \((z\sim 2-3)\) than today. Their size evolution can be explained by collisionless dynamical processes in galaxy mergers which, however, fail to reproduce the diffuse low-density central cores in the local massive early-type galaxies (ETGs). We use sequences of major and minor merger N-body simulations starting with compact spherical and disc-like progenitor models to investigate the impact of supermassive black holes (SMBHs) on the evolution of the galaxies. With the KETJU code we accurately follow the collisional interaction of the SMBHs with the nearby stellar population and the collisionless evolution of the galaxies and their dark matter haloes. We show that only models including SMBHs can simultaneously explain the formation of low-density cores up to sizes of \(R_\mathrm{b} \sim 1.3\) kpc with mass deficits in the observed range and the rapid half-mass size evolution. In addition, the orbital structure in the core region (tangentially biased orbits) is consistent with observation-based results for local cored ETGs. The displacement of stars by the SMBHs boost the half-mass size evolution by up to a factor of 2 and even fast rotating progenitors (compact quiescent discs) lose their rotational support after 6-8 mergers. We conclude that the presence of SMBHs is required for merger-driven evolution models of high-redshift red nuggets into local ETGs.