Dwarf Galaxy Starburst Statistics in the Local Volume

TL;DR

This study quantifies how often dwarf galaxies experience starbursts, finding that only about 6% are in a burst phase at any time, and these bursts contribute roughly 25% to their total star formation, informing galaxy evolution models.

Contribution

First comprehensive analysis of starburst prevalence and characteristics in local dwarf galaxies using H-alpha and UV data from the 11HUGS survey.

Findings

Approximately 6% of dwarf galaxies are in a starburst phase at any given time.

Starbursts account for about 25% of total star formation in dwarf galaxies.

Most low-mass galaxies continue forming stars without experiencing massive bursts.

Abstract

An unresolved question in galaxy evolution is whether the star formation histories of low mass systems are preferentially dominated by starbursts or modes that are more quiescent and continuous. Here, we quantify the prevalence of global starbursts in dwarf galaxies at the present epoch, and infer their characteristic durations and amplitudes. The analysis is based on the H-alpha component of the 11 Mpc H-alpha UV Galaxy Survey (11HUGS), which is providing H-alpha and GALEX UV imaging for an approximately volume-limited sample of ~300 star-forming galaxies within 11 Mpc. We first examine the completeness properties of the sample, and then directly tally the number of bursting dwarfs and compute the fraction of star formation that is concentrated in such systems. Our results are consistent with a picture where dwarfs that are currently experiencing massive global bursts are just the ~6% tip of a low-mass galaxy iceberg. Moreover, bursts are only responsible for about a quarter of the total star formation in the overall dwarf population, so the majority of stars in low-mass systems are not formed in this mode today. Spirals and irregulars devoid of H-alpha emission are rare, indicating that the complete cessation of star formation generally does not occur in such galaxies and is not characteristic of the inter-burst state, at least for the more luminous systems with M(B)<-15. The starburst statistics presented here directly constrain the duty cycle and the average burst amplitude under the simplest assumptions where all dwarf irregulars share a common star formation history and undergo similar bursts cycles with equal probability. Uncertainties in such assumptions are discussed in the context of previous work.