Scaling Relations Between Warm Galactic Outflows and Their Host Galaxies

TL;DR

This study analyzes warm galactic outflows in 51 nearby star-forming galaxies, revealing how outflow properties correlate with galaxy characteristics and suggesting supernovae as the primary driving mechanism.

Contribution

It provides new empirical scaling relations between outflow velocities, mass outflow rates, and galaxy properties, highlighting the role of supernovae in powering these outflows.

Findings

Outflow velocity correlates with SFR, stellar mass, and circular velocity.

Mass outflow rate scales with SFR and stellar mass.

Galaxies below a certain mass threshold tend to lose gas, affecting metallicity.

Abstract

We report on a sample of 51 nearby, star-forming galaxies observed with the Cosmic Origin Spectrograph on the Hubble Space Telescope. We calculate Si II kinematics and densities arising from warm gas entrained in galactic outflows. We use multi-wavelength ancillary data to estimate stellar masses (M$_\ast$), star-formation rates (SFR), and morphologies. We derive significant correlations between outflow velocity and SFR$^{\sim 0.1}$, M$_\ast^{\sim 0.1}$ and v$_\text{circ}^{\sim 1/2}$. Some mergers drive outflows faster than these relations prescribe, launching the outflow faster than the escape velocity. Calculations of the mass outflow rate reveal strong scaling with SFR$^{\sim 1/2}$ and M$_\ast^{\sim 1/2}$. Additionally, mass-loading efficiency factors (mass outflow rate divided by SFR) scale approximately as M$_\ast^{-1/2}$. Both the outflow velocity and mass-loading scaling suggest that these outflows are powered by supernovae, with only 0.7% of the total supernovae energy converted into the kinetic energy of the warm outflow. Galaxies lose some gas if log(M$_\ast$/M$_\odot$) < $9.5$, while more massive galaxies retain all of their gas, unless they undergo a merger. This threshold for gas loss can explain the observed shape of the mass-metallicity relation.