CIV absorption from hot gas inside the supergiant shell LMC4 observed with HST and IUE.

Abstract

High resolution ultraviolet spectra obtained with the HST-GHRS of two stars in the direction of the supergiant shell LMC4 unambiguously show absorption by substantial quantities of CIV gas at velocities near the the systemic velocity of the LMC. In combination with the detection of diffuse X-rays from the LMC4 by ROSAT and other supporting data, this demonstrates that the interior of LMC4 is filled with tenuous hot gas. CIV interstellar absorption is seen over a large velocity range, having at least 2 components at about 280 and 320km/s. The strong component at 280km/s has a width of 40km/s and a column density in the order of 3x10^13^cm^-2^. The width of the absorption is best explained by bulk motions of CIV-containing gas clouds inside LMC4. These hot clouds or layers around cold clouds have to have a relatively high filling factor inside LMC4 to fit the observations. The characteristics of the CIV gas component at 320km/s are such that they trace a blast wave from a recent supernova within the LMC4 cavity. Galactic CIV absorption due to halo gas is also present, as to be expected for these lines of sight.