Gas and dust budget of the Large Magellanic Cloud

Recent observations from the Spitzer Space Telescope enable us to study the mid-infrared dust excess of Asymptotic giant branch (AGB) stars in the Large Magellanic Cloud (LMC). Using mid-infrared spectra, together with photometric data from the SAGE programme, we establish a colour selection of carbon-rich AGB stars with intermediate and high mass-loss rates. We also established mass-loss rate versus colour relations for carbon-rich AGB stars. The integrated mass-loss rate over all intermediate and high mass-loss rate carbon-rich AGB candidates in the LMC is 8.5x10^-3 solar mass per year. This number could be almost doubled if oxygen-rich stars are included. Gas mass-loss rate from these stars is 4-5x10^-4 solar mass per year per kpc2 in the bar and1x10^-4 solar mass per year per kpc^2 outside of the bar. AGB stars are one of the most important dust sources in the LMC, and the dominant gas source outside of the bar. As a consequence of recent increases in the star-formation rate, supernovae are the most important gas source in the LMC bar and around 30 Dor. These differences in dust and gas sources impact on the gas-to-dust ratio and dust properties of the local ISM, because the injection from SNe could have a higher gas-to-dust ratio, resulting in a higher gas-to-dust ratio for the ISM in certain regions of the LMC.