Structure of the Interstellar Medium in the Magellanic Clouds
Abstract
Ca II absorption spectra of 25 early-type Magellanic Cloud supergiants, presented here, have been obtained at a resolution of 5 km s^-1^ using the newly commissioned coude echelle spectrograph of the AAT. They are used in conjunction with H I observations from the Parkes 64 m radio telescope and polarization observations to reveal the three-dimensional structure of the Large and Small Magellanic Clouds. A large-scale grid map of H I in and around the Magellanic System shows that the intermediate-velocity gas components seen in the direction of the LMC have differing origins; the 60 km s^-1^ component is galactic, the 130 km s^-1^ component is galactic (or possibly tidally torn Magellanic gas), and the 170 km s^-1^ component is LMC gas. The gas in both Magellanic Clouds is seen to have a distance-velocity association also seen in the stellar component of the SMC (Mathewson et al.). This relation breaks down south of 30 Doradus, where the gas structure is complex. Radio and optical polarization measurements are shown to agree, indicating that there is no significant line-of-sight structure to the aligned magnetic field visible in either the LMC or SMC. The pan-Magellanic field originally proposed by Mathewson and Ford finds support from a reanalysis of past optical polarization measurements, and a spiral field centered on 30 Doradus is clearly revealed. The spiral field merges smoothly with the pan-Magellanic field in the LMC, suggesting a common cause for both phenomena, a collision of the SMC with the LMC. The idea of a collision of the LMC and SMC as put forward in the models of Murai and Fujimoto and Mathewson et al. is supported by the new observations.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- June 1990
- DOI:
- 10.1086/168782
- Bibcode:
- 1990ApJ...355..473W
- Keywords:
-
- Galactic Evolution;
- Interstellar Matter;
- Magellanic Clouds;
- Absorption Spectra;
- Emission Spectra;
- Interstellar Magnetic Fields;
- Polarized Radiation;
- Radio Emission;
- Astrophysics;
- GALAXIES: INTERSTELLAR MATTER;
- GALAXIES: MAGELLANIC CLOUDS;
- GALAXIES: STRUCTURE;
- MAGNETIC FIELDS;
- POLARIZATION;
- RADIO SOURCES: 21 CM RADIATION