First Detection of HCO$^+$ Absorption in the Magellanic System

TL;DR

This study reports the first detection of HCO$^+$ absorption in the Magellanic System, revealing molecular presence in a low-density environment and suggesting dynamic processes influence molecule survival.

Contribution

It provides the first observational evidence of HCO$^+$ absorption in the Magellanic System, expanding understanding of molecular gas in low-metallicity, diffuse environments.

Findings

HCO$^+$ absorption detected towards one source behind the Magellanic Bridge.

Absorber located at LSR velocity of 214 km/s with specific line properties.

Low HI column density and little dust or CO emission at the absorber site.

Abstract

We present the first detection of HCO$^+$ absorption in the Magellanic System. Using the Australia Telescope Compact Array (ATCA), we observed 9 extragalactic radio continuum sources behind the Magellanic System and detected HCO$^+$ absorption towards one source located behind the leading edge of the Magellanic Bridge. The detection is located at LSR velocity of $v=214.0 \pm 0.4\rm\,km\,s^{-1}$, with a full width at half maximum of $\Delta v=4.5\pm 1.0\rm\,km\,s^{-1}$ and optical depth of $\tau(\rm HCO^+)=0.10\pm 0.02$. Although there is abundant neutral hydrogen (HI) surrounding the sightline in position-velocity space, at the exact location of the absorber the HI column density is low, $<10^{20}\rm\,cm^{-2}$, and there is little evidence for dust or CO emission from Planck observations. While the origin and survival of molecules in such a diffuse environment remains unclear, dynamical events such as HI flows and cloud collisions in this interacting system likely play an important role.