ABSTRACT
Supermassive black holes (SMBHs) are indispensable components of galaxy ecosystems. Their origin, growth, and feedback to the host galaxies are among the most fundamental questions in galaxy formation. In this talk, I will introduce a theoretical framework that coherently describes the formation of SMBHs from their seeding epoch to the present within the cosmological context. I will show that these seeds are remnants of the first-generation (Pop-III) stars, whose formation is active in pristine mini-halos at z ~ 10--40, and ceases by z ~ 5 when the intergalactic medium (IGM) becomes enriched. The critical factors governing seed breeding are local radiation environment and halo assembly, indicating that the effects of environment and assembly bias -- concepts that have been extensively explored in the local Universe, are already prevalent at such high redshifts. The dynamically hot and thermally cold nature of the turbulent interstellar medium (ISM) in any high-z galaxy induces rapid cooling, cancellation of angular momentum, and gas inflow towards the galactic center, leading to nuclear burst that triggers the formation of nuclear star cluster (NSC), hyper-Eddington accretion onto the seed, and temporary quenching of the host galaxy. SMBH growth at z >~ 5 is thus expected to be dominated by episodic hyper-Eddington bursts, each lasting only ~ 10-100 kyr, and gradually migrating to a phase of more quiescent sub-Eddington growth towards z=0. We design a semi-analytical model that implements these ideas to forecast the formation and evolution of galaxy ecosystems from z = 40--0, with nested refinement engines connecting large-scale structures, halos, galaxies, dense star clusters, and SMBHs. These ideas intuitively account for the recent JWST observations at high z, including the emergence of highly clumpy star formations, massive/quiescent galaxies, and overmassive black holes, although further data is required to test and refine the model assumptions. High-resolution hydrodynamical simulations with successive refinements are essential to clarify the detailed physical processes at each level of the cosmic hierarchy.
