A study of the cool gas in the Large Magellanic Cloud I. Properties of thecool atomic phase - a third HI absorption survey

The cool atomic interstellar medium of the Large Magellanic Cloud (LMC) see ms to be quite different from that in the Milky Way. In a series of three p apers we study the properties of the cool atomic hydrogen in the LMC (Paper I), its relation to molecular clouds using SEST-CO-observations (Paper II) and the cooling mechanism of the atomic gas based on ISO-[C II] investigat ions (Paper III). In this paper we present the results of a third 21 cm absorption line surve y toward the LMC carried out with the Australia Telescope Compact Array(1) (ATCA). 20 compact continuum sources, which are mainly in the direction of the supergiant shell LMC 4, toward the surroundings of 30 Doradus and towar d the eastern steep H I boundary, have been chosen from the 1.4 GHz snapsho t continuum survey of Marx et al. We have identified 20 absorption features toward nine of the 20 sources. The proper ties of the cool H I clouds are investigated and are compared for the different regions of the LMC taking t he results of Dickey et al. (survey 2) into account. We find that the cool H I gas in the LMC is either unusually abundant compa red to the cool atomic phase of the Milky Way or the gas is clearly colder (T-C approximate to 30 K) than that in our Galaxy (T-C approximate to 60 K) . The properties of atomic clouds toward 30 Doradus and LMC 4 suggest a hig her cooling rate in these regions compared to other parts of the LMC, proba bly due to an enhanced pressure near the shock fronts of LMC 4 and 30 Dorad us. The detected cool atomic gas toward the eastern steep H I boundary migh t be the result of a high compression of gas at the leading edge.