The long lives of giant clumps and the birth of outflows in gas-rich galaxies at high redshift

TL;DR

This study uses high-resolution simulations to show that giant clumps in high-redshift galaxies survive stellar feedback, produce significant outflows, and migrate inward, contributing to galaxy bulge formation.

Contribution

It demonstrates that giant clumps can survive for hundreds of Myr and sustain outflows, challenging previous ideas of rapid dispersal.

Findings

Giant clumps produce outflows comparable to their star formation rates.

Clumps survive stellar feedback and migrate inward over hundreds of Myr.

Simulated outflow properties match observational data.

Abstract

Star-forming disk galaxies at high redshift are often subject to violent disk instability, characterized by giant clumps whose fate is yet to be understood. The main question is whether the clumps disrupt within their dynamical timescale (<50Myr), like molecular clouds in today's galaxies, or whether they survive stellar feedback for more than a disk orbital time (~300Myr) in which case they can migrate inward and help building the central bulge. We present 3.5-7pc resolution AMR simulations of high-redshift disks including photo-ionization, radiation pressure, and supernovae feedback (Renaud et al. 2013, and Perret et al., this astro-ph issue). Our modeling of radiation pressure determines the mass loading and initial velocity of winds from basic physical principles. We find that the giant clumps produce steady outflow rates comparable to and sometimes somewhat larger than their star formation rate, with velocities largely sufficient to escape galaxy. The clumps also lose mass, especially old stars, by tidal stripping, and the stellar populations contained in the clumps hence remain relatively young (<=200Myr), as observed. The clumps survive gaseous outflows and stellar loss, because they are wandering in gas-rich turbulent disks from which they can re-accrete gas at high rates compensating for outflows and tidal stripping, overall keeping realistic and self-regulated gaseous and stellar masses. Our simulations produce gaseous outflows with velocities, densities and mass loading consistent with observations, and at the same time suggest that the giant clumps survive for hundreds of Myr and complete their migration to the center of high-redshift galaxies, without rapid dispersion and reformation of clumps.