# The Ionization and Dynamics of the Makani Galactic Wind

## TL;DR

This study uses optical spectra to analyze the ionized gas in the Makani galaxy's galactic wind, revealing its mass, velocity, and energy, and suggesting a momentum-driven flow influenced by starburst activity.

## Contribution

First detailed spectroscopic analysis of the Makani galaxy's galactic wind, constraining the physical state, mass, and dynamics of its ionized component across different wind episodes.

## Key findings

- Ionized gas mass in Episode II wind ~ 1-2 x 10^9 solar masses
- Outflow rate in Episode II ~ 170-250 solar masses per year
- Wind driven by momentum from hot ejecta and radiation pressure

## Abstract

The Makani galaxy hosts the poster child of a galactic wind on scales of the circumgalactic medium. It consists of a two-episode wind in which the slow, outer wind originated 400 Myr ago (Episode I; R_I = 20-50 kpc) and the fast, inner wind is 7 Myr old (Episode II; R_II = 0-20 kpc). While this wind contains ionized, neutral, and molecular gas, the physical state and mass of the most extended phase--the warm, ionized gas--is unknown. Here we present Keck optical spectra of the Makani outflow. These allow us to detect hydrogen lines out to r = 30-40 kpc and thus constrain the mass, momentum, and energy in the wind. Many collisionally-excited lines are detected throughout the wind, and their line ratios are consistent with 200-400 km/s shocks that power the ionized gas, with v_shock = $\sigma$_wind. Combining shock models, density-sensitive line ratios, and mass and velocity measurements, we estimate that the ionized mass and outflow rate in the Episode II wind could be as high as that of the molecular gas: M_II(HII) ~ M_II(H_2) = (1-2)x10^9 Msun and dM/dt_II(HII) ~ dM/dt_II(H_2) = 170-250 Msun/yr. The outer wind has slowed, so that dM/dt_I(HII) ~ 10 Msun/yr, but it contains more ionized gas: M_I(HII) = 5x10^9 Msun. The momentum and energy in the recent Episode II wind imply a momentum-driven flow (p ``boost" ~ 7) driven by the hot ejecta and radiation pressure from the Eddington-limited, compact starburst. Much of the energy and momentum in the older Episode I wind may reside in a hotter phase, or lie further into the CGM.