Down-the-barrel and transverse observations of the Large Magellanic Cloud: evidence for a symmetrical galactic wind on the near and far sides of the galaxy

TL;DR

This study uses UV absorption-line observations to reveal a symmetrical, large-scale galactic wind in the Large Magellanic Cloud, driven by recent star formation, with implications for gas removal processes in dwarf galaxies.

Contribution

It provides the first direct evidence of a symmetrical galactic wind on both sides of the LMC disk using combined UV absorption data, highlighting the wind's multiphase nature and environmental influences.

Findings

Gas flows away from the disk at up to 100 km/s

The outflow is multiphase, involving photoionization and collisional ionization

Estimated outflow rate exceeds 0.4 solar masses per year

Abstract

We compare the properties of gas flows on both the near and far side of the Large Magellanic Cloud (LMC) disk using Hubble Space Telescope UV absorption-line observations toward an AGN behind (transverse) and a star within (down-the-barrel) the LMC disk at an impact parameter of 3.2 kpc. We find that even in this relatively quiescent region gas flows away from the disk at speeds up to $\sim$100 km/s in broad and symmetrical absorption in the low and high ions. The symmetric absorption profiles combined with previous surveys showing little evidence that the ejected gas returns to the LMC and provide compelling evidence that the LMC drives a global, large-scale outflow across its disk, which is the likely result of a recent burst of star formation in the LMC. We find that the outflowing gas is multiphase, ionized by both photoionization (SiII and SiIII) and collisional ionization (SiIV and CIV). We estimate a total mass and outflow rate to be $>10^7$ Msun and $>0.4$ Msun/yr. Since the velocity of this large-scale outflow does not reach the LMC escape velocity, the gas removal is likely aided by either ram-pressure stripping with the Milky Way halo or tidal interactions with the surrounding galaxies, implying that the environment of LMC-like or dwarf galaxies plays an important role in their ultimate gas starvation. Finally we reassess the mass and plausible origins of the high-velocity complex toward the LMC given its newly-determined distance that places it in the lower Milky Way halo and sky-coverage that shows it extends well beyond the LMC disk.