Physical Conditions of the Ionized Superwind in NGC 253 with VLT/MUSE

TL;DR

This study uses VLT/MUSE integral field spectroscopy to analyze the ionized gas in NGC 253's superwind, revealing high velocities, shock ionization, and quantifying the outflow's mass and energy properties.

Contribution

It provides detailed kinematic, ionization, and density measurements of the ionized superwind in NGC 253, utilizing multi-component line decomposition and integral field spectroscopy for the first time.

Findings

Maximum outflow velocity ~ -500 km/s

Electron densities peak at 2100 cm$^{-3}$ near the nucleus

Mass-outflow rate ~ 0.4 M$_{ ext{sun}}$/year

Abstract

We present an analysis of the H$\alpha$-emitting ionized gas in the warm phase of the NGC 253 outflow using integral field spectroscopy from the Multi Unit Spectroscopic Explorer (MUSE). In each spaxel, we decompose H$\alpha$, [N II], and [S II] emission lines into a system of up to 3 Gaussian components, accounting for the velocity contributions due to the disk and both intercepted walls of an outflow cone. In the approaching southern lobe of the outflow, we find maximum deprojected outflow velocities down to ~ -500 km/s. Velocity gradients of this outflowing gas range from ~ -350 to -550 km/s/kpc with increasing distance from the nucleus. Additionally, [N II]/H$\alpha$ and [S II]/H$\alpha$ integrated line ratios are suggestive of shocks as the dominant ionization source throughout the wind. Electron densities, inferred from the [S II] doublet, peak at 2100 cm$^{-3}$ near the nucleus and reach $\lesssim 50 $cm$^{-3}$ in the wind. Finally, at an uncertainty of 0.3 dex on the inferred mass of $4\times10^{5}$ M$_{\odot}$, the mass-outflow rate of the H$\alpha$-emitting gas in the southern outflow lobe is ~ 0.4 M$_{\odot}$/year. This yields a mass-loading factor of $\eta$ ~ 0.1 and a ~ 2% starburst energy efficiency.