Clump Survival and Migration in VDI Galaxies: an Analytic Model versus Simulations and Observations

TL;DR

This paper develops an analytic model for giant clumps in high-redshift galaxies, comparing it with simulations and observations to understand their longevity and migration behavior.

Contribution

It introduces a comprehensive 'bathtub' model for clump evolution, validated against simulations and observations, to distinguish long-lived migrating clumps from short-lived ones.

Findings

The model aligns with simulations with moderate feedback.

Observed clumps are consistent with long-lived, migrating clumps.

The inverse specific SFR serves as a clump age indicator.

Abstract

We address the nature of the giant clumps in high-z galaxies that undergo Violent Disc Instability, attempting to distinguish between long-lived clumps that migrate inward and short-lived clumps that disrupt by feedback. We study the evolution of clumps as they migrate through the disc using an analytic model tested by simulations and confront theory with CANDELS observations. The clump ``bathtub" model, which considers gas and stellar gain and loss, is characterized by four parameters: the accretion efficiency, the star-formation-rate (SFR) efficiency, and the outflow mass-loading factors for gas and stars. The relevant timescales are all comparable to the migration time, two-three orbital times. A clump differs from a galaxy by the internal dependence of the accretion rate on the varying clump mass. The analytic solution, involving exponential growing and decaying modes, reveals a main evolution phase during the migration, where the SFR and gas mass are constant and the stellar mass is rising linearly with time. This makes the inverse of the specific SFR an observable proxy for clump age. Later, the masses and SFR approach an exponential growth with a constant specific SFR, but this phase is hypothetical as the clump disappears in the galaxy center. The model matches simulations with different, moderate feedback, both in isolated and cosmological settings. The observed clumps agree with our theoretical predictions, indicating that the massive clumps are long-lived and migrating. A non-trivial challenge is to model feedback that is non-disruptive in massive clumps but suppresses SFR to match the galactic stellar-to-halo mass ratio.