A detection of H$_2$ in a high velocity cloud toward the Large Magellanic Cloud

TL;DR

This paper reports the discovery of molecular hydrogen in a high velocity cloud near the LMC, providing insights into the composition and dynamics of halo clouds and their possible origins.

Contribution

It presents the first detection of H$_2$ in a high velocity cloud associated with the LMC or Milky Way, expanding knowledge of halo cloud composition.

Findings

H$_2$ column density of 10^{17.5} cm$^{-2}$

Cloud temperature approximately 75 K

Possible connection to Galactic fountain or LMC outflow

Abstract

This work presents a new detection of H$_2$ absorption arising in a high velocity cloud (HVC) associated with either the Milky Way or the Large Magellanic Cloud (LMC). The absorber was found in an archival Far Ultraviolet Spectroscopic Explorer spectrum of the LMC star Sk-70$^\circ$32. This is the fifth well-characterized H$_2$ absorber to be found in the Milky Way's halo and the second such absorber outside the Magellanic Stream and Bridge. The absorber has a local standard of rest central velocity of $+$140 km s$^{-1}$ and a H$_2$ column density of $10^{17.5}$ cm$^{-2}$. It is most likely part of a cool and relatively dense inclusion ($T\approx 75$ K, $n_{\rm H}\sim 100$ cm$^{-3}$) in a warmer and more diffuse halo cloud. This halo cloud may be part of a still-rising Milky Way Galactic fountain flow or an outflow from the Large Magellanic Cloud.