Conditions for clump survival in High-zdisc galaxies

Abstract

ABSTRACTWe study the survival of giant clumps in high-redshift disc galaxies, short-lived (S) versus long-lived (L), and two L subtypes, via analytic modelling and simulations. We develop a criterion for clump survival, with/without gas, based on a survivability parameter S. It compares the energy sources by supernova feedback and gravitational contraction to the clump binding energy and losses by outflows and turbulence dissipation. The clump properties are derived from Toomre instability, approaching virial/Jeans equilibrium, and the supernova energy deposit uses an up-to-date bubble analysis. For moderate feedback, we find L clumps with circular velocities ${\sim}50\, {\rm km}\, {\rm s}^{-1}$ and masses ≥108 M⊙. They favour galaxies with circular velocities ${\ge}200\, {\rm km\,s}^{-1}$, consistent at z ∼ 2 with the typical disc stellar mass, ≥109.3 M⊙. L clumps favour disc gas fractions ≥0.3, low-mass bulges, and z ∼ 2. They disfavour more effective feedback due to, e.g. supernova clustering, very strong radiative feedback, top-heavy stellar mass function, or particularly high star-formation-rate (SFR) efficiency. A subtype of L clumps (LS), which lose their gas in several free-fall times but retain bound stellar components, may be explained by less contraction and stronger gravitational effects, where clump mergers increase the SFR efficiency. These may give rise to globular clusters. The more massive L clumps (LL) retain most of their baryons for tens of free-fall times with a roughly constant star-formation rate.