First Detection of HCO+ Absorption in the Magellanic System
Murray, Claire E.; Stanimirović, Snežana; Wong, Tony; McClure-Griffiths, N. M.; Dickey, John M.; Dawson, J. R.; Richter, P.; Putman, M. E.; Allison, J. R.; Lindner, Robert R.; Liszt, H. S.; Babler, Brian L.
United States, Australia, Germany
Abstract
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 {{Δ }}v=4.5+/- 1.0 {km} {{{s}}}-1, and an optical depth of τ ({{HCO}}+)=0.10+/- 0.02. Although there is abundant neutral hydrogen (H i) surrounding the sight line in position-velocity space, at the exact location of the absorber the H i column density is low, \lt {10}20 {{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 H i flows and cloud collisions in this interacting system likely play an important role.