First detection of HCO+ absorption in the Magellanic System

We present the first detection of HCO⁺ absorption in the Magellanic System. Using the ATCA, we observed nine extragalactic radio continuum sources behind the Magellanic System and detected HCO⁺ absorption toward one source located behind the leading edge of the Magellanic Bridge. The detection is located at an LSR velocity of v = 214.0 ± 0.4 km s^-1, with an FWHM of Δv = 4.5 ± 1.0 km s^-1, and an optical depth of τ(HCO⁺) = 0.10 ± 0.02. Although there is abundant neutral hydrogen (HI) surrounding the sight line in position–velocity space, at the exact location of the absorber the HI column density is low, <10²⁰ 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 remain unclear, dynamical events such as HI flows and cloud collisions in this interacting system likely play an important role.