Multi-Wavelength Observations of the Multi-Phase ISM

A variety of observing facilities have been used to study the multi-phase ISM of the LMC. For the 10 K ionized gas, emission-line images were taken with a CCD camera on the Curtis Schmidt telescope at Cerro Tololo Inter-American Observatory (CTIO), and long-slit high-dispersion spectra were taken with the echelle spectrograph on the CTIO 4m telescope. The emission-line (H, [Oá III], and [Sá II]) images show the distribution and excitation of the ionized gas (Smith et al. 1997), while the echelle spectra show the internal motion and shocks in the ionized gas (e.g., Chu & Kennicutt 1994).

The 10 K ionized gas has been studied with interstellar absorption line observations in the UV, using Cá IVá 1548,1550, Siá IV1393,1402, and Ná Vá 1238,1242 lines. A large number of high-dispersion spectra of early-type stars in the LMC are available in the International Ultraviolet Explorer archives. These spectra are useful in diagnosing shocks inside superbubbles or supergiant shells, but provide no information on the hot gas halo of the LMC (Chu et al. 1994). The Goddard High Resolution Spectrograph (GHRS) on-board the Hubble Space Telescope (HST) has been used to take high-dispersion spectra with high S/N. With a careful selection of cool probe stars in quiescent interstellar environments, it is possible to determine not only the column density but also the kinematics of the 10 K gas halo of the LMC (Wakker et al. 1997).

The 10 K ionized gas is best observed in soft X-rays. The ROSAT X-ray satellite provides two detectors: the Position Sensitive Proportional Counter (PSPC) and the High Resolution Imager (HRI). The PSPC, sensitive to 0.1-2.4 keV, has an on-axis angular resolution of and a spectral resolution of 45% at 1 keV. The HRI, sensitive to 0.1-2.0 keV, has an on-axis resolution of , but has essentially no spectral resolution. Both the PSPC and the HRI have been used to survey the LMC (Snowden & Petre 1994; Chu, Snowden, & Chang 1996).

The HI distribution in the LMC has been mapped with the Parkes 64m telescope at an angular resolution of (Rohlfs et al. 1984). An HI mosaic of the LMC has recently been obtained with the Australia Telescope Compact Array (ATCA) at a resolution of 1' (Kim et al. 1997a).

The molecular gas in the LMC has been mapped at a resolution of 8'.8 in the J = 1 0 rotational transition of CO (Cohen et al. 1988). A more recent CO survey of the LMC was carried out with the Swedish-ESO Submillimeter Telescope (SEST) at a resolution of 45'' (Israel et al. 1993). The SEST CO maps of two star-formation regions, 30 Dor and N11, have been presented by Caldwell & Kutner (1996).

á© Copyright Astronomical Society of Australia 1997