Accelerating Galaxy Winds During the Big Bang of Starbursts

TL;DR

This paper introduces a new method to measure the properties of galaxy outflows during starbursts, revealing that winds accelerate and grow in size, with implications for galaxy evolution and feedback processes.

Contribution

The study develops a novel approach combining spectral modeling and absorption lines to infer wind radii and acceleration, providing new insights into outflow dynamics during starbursts.

Findings

Winds accelerate throughout the starburst phase.

Winds reach radii of ~1 kpc in ~10 Myr.

Cool outflows account for about 10% of stellar feedback energy at 10 Myr.

Abstract

We develop a new method to infer the temporal, geometric, and energetic properties of galaxy outflows, by combining stellar spectral modeling to infer starburst ages, and absorption lines to measure velocities. If winds are accelerated with time during a starburst event, then these two measurements enable us to solve for the wind radius, similarly to length scales and the Hubble parameter in Big Bang cosmology. This wind radius is the vital, but hard-to-constrain parameter in wind physics. We demonstrate the method using spectra of 87 starburst galaxies at z=0.05-0.44, finding that winds accelerate throughout the starburst phase and grow to typical radii of ~1 kpc in ~10 Myr. Mass flow rates increase rapidly with time, and the mass-loading factor exceeds unity at about 10 Myr - while still being accelerated, the gas will likely unbind from the local potential and enrich the circumgalactic medium. We model the mechanical energy available from stellar winds and supernovae, and estimate that a negligible amount is accounted for in the cool outflow at early times. However, the energy deposition increases rapidly and ~10% of the budget is accounted for in the cool flow at 10 Myr, similar to some recent hydrodynamical simulations. We discuss how this model can be developed, especially for high-redshift galaxies.