Starbursts in isolated galaxies. I. The influence of stellar birth function and IMF

TL;DR

This study investigates the stability and starburst modes in isolated dwarf galaxies by examining the effects of the stellar birth function, IMF, feedback, and ISM, revealing quasi-periodic starbursts driven by gas density variations.

Contribution

It introduces a coupled dynamical and internal property model showing starburst behavior is insensitive to star formation details and driven by gas density oscillations.

Findings

Quasi-periodic starbursts occur due to virial oscillations.

Star formation rate closely follows equilibrium rates due to short cooling times.

Starburst behavior is robust against variations in the stellar birth function and IMF.

Abstract

Starbursts and substantial variations in the star formation histories are a common phenomenon in galaxies. We study the stability properties of isolated star-forming dwarf galaxies with the aim of identifying starburst modes. The impact of the stellar birth function, the initial mass function (IMF), the stellar feedback and the interstellar medium (ISM) model are investigated. We apply a one-zone model for a star-gas system coupled by mass and energy transfer. Additionally, we extend the network for active dynamical evolution. This allows for a coupling between the dynamical state of the galaxy and its internal properties. While the influence of the dynamics on the total star formation rate is strong, the coupling of the internal properties (gas temperature) on the dynamics is rather limited, because radiative cooling keeps the gas temperature well below the virial temperature. Because of short cooling and feedback timescales, the star formation rate is close to the equilibrium star formation rates. Quasi-periodic starbursts occur, because star formation follows the variations in the gas density induced by decaying virial oscillations. This behaviour is quite insensitive to the nature and the details of the stellar birth description, viz. whether spontaneous or induced star formation is considered or the IMF is varied. A second type of burst is found as an instability operating when the cooling may drop at very low densities with increasing temperature. Bursts of star formation occur during transitory phases, when dynamical equilibrium is established. Then they are quasi-periodic on the dynamical timescale. Because of short heating and cooling timescales, the star formation rate follows the equilibrium star formation rate corresponding to the actual gas density.