Bulge growth through disk instabilities in high-redshift galaxies

TL;DR

This paper reviews how violent disk instabilities at high redshift lead to rapid bulge growth through giant clump migration, gas inflows, and concurrent growth of black holes and thick disks, contrasting with slow secular processes in modern galaxies.

Contribution

It provides a comprehensive overview of high-redshift disk instabilities and their role in rapid bulge formation, highlighting differences from low-redshift secular evolution.

Findings

High-redshift disks are globally unstable and fragment into giant clumps.

Giant clumps migrate inward and coalesce into bulges within 10^8 years.

Violent instabilities drive intense gas inflows and concurrent growth of black holes.

Abstract

The role of disk instabilities, such as bars and spiral arms, and the associated resonances, in growing bulges in the inner regions of disk galaxies have long been studied in the low-redshift nearby Universe. There it has long been probed observationally, in particular through peanut-shaped bulges. This secular growth of bulges in modern disk galaxies is driven by weak, non-axisymmetric instabilities: it mostly produces pseudo-bulges at slow rates and with long star-formation timescales. Disk instabilities at high redshift (z>1) in moderate-mass to massive galaxies (10^10 to a few 10^11 Msun of stars) are very different from those found in modern spiral galaxies. High-redshift disks are globally unstable and fragment into giant clumps containing 10^8-10^9 Msun of gas and stars each, which results in highly irregular galaxy morphologies. The clumps and other features associated to the violent instability drive disk evolution and bulge growth through various mechanisms, on short timescales. The giant clumps can migrate inward and coalesce into the bulge in a few 10^8 yr. The instability in the very turbulent media drives intense gas inflows toward the bulge and nuclear region. Thick disks and supermassive black holes can grow concurrently as a result of the violent instability. This chapter reviews the properties of high-redshift disk instabilities, the evolution of giant clumps and other features associated to the instability, and the resulting growth of bulges and associated sub-galactic components.