Properties and origin of the high-velocity gas toward the Large Magellanic Cloud.
LEHNER N., STAVELEY-SMITH L. and HOWK J.C.
Abstract (from CDS):
In the spectra of 139 early-type Large Magellanic Cloud (LMC) stars observed with Far Ultraviolet Spectroscopic Explorer and with deep radio Parkes H I 21 cm observations along with those stars, we search for and analyze the absorption and emission from high-velocity gas at +90 ≤ vLSR ≤ +175 km/s. The H I column density of the high-velocity clouds (HVCs) along these sightlines ranges from <1018.4 to 1019.2/cm2. The incidence of the HVC metal absorption is 70%, significantly higher than the H I emission occurrence of 32%. We find that the mean metallicity of the HVC is [O I/H I] = -0.51±0.120.16. There is no strong evidence for a large variation in the HVC metallicity, implying that these HVCs have a similar origin and are part of the same complex. The mean and scatter of the HVC metallicities are more consistent with the present-day LMC oxygen abundance than that of the Small Magellanic Cloud or the MW. We find that on average [Si II/O I] = +0.48±0.150.25 and [Fe II/O I] = +0.33±0.140.21, implying that the HVC complex is dominantly ionized. The HVC complex has a multiphase structure with neutral (O I, Fe II), weakly ionized (Fe II, N II), and highly ionized (O VI) components, and has evidence of dust but no molecules. All the observed properties of the HVC can be explained by an energetic outflow from the LMC. This is the first example of a large (>106 M☉) HVC complex that is linked to stellar feedback occurring in a dwarf spiral galaxy.