The intergalactic medium towards supernova 1987A

Abstract

The galactic halo and the intergalactic medium have been investigated by analysis of absorption features in the spectra of Seyfert galaxies, quasars, globular clusters, high-latitude stars and Magellanic Cloud supergiants1. The halo gas is thus thought to be distributed in an expanded disk not more than 10 kpc thick. But radioastronomy observations have revealed other structures, the high-velocity clouds, which are probably associated with the galactic halo. They are seen particularly in the direction of the Magellanic Clouds, where the Magellanic Stream seems to merge2–5. The extraordinary brightness of supernova 1987A in the Large Magellanic Cloud (LMC) allowed us to obtain high-resolution spectra with high signal-to-noise ratios, sampling the galactic disk and halo, interstellar gas in the LMC, and the intervening medium. Thirty-five distinct components have been clearly identified, prob-ably located between the Galaxy and the LMC, and showing low dust content.