Modeling Quasar Absorption Spectra Of Metals And High-velocity Clouds

High-velocity clouds (HVCs) were first detected by HI 21cm emission in 1963, since then the nature of HVCs remains controversial although more than forty years has been past. In the last decade, with the observations of high resolutions, the developments of theoretical models and numerical simulations, there have been great progresses in many aspects of the studies of high-velocity clouds, particularly for some special kinds and the all-sky surveys. Main progresses are reviewed including the observational studies of the two kinds of newly-found CHVCs and highly-ionized HVCs as a whole or individually, the high-resolution observations of Magellanic Stream and Complex C which are the largest HVCs in Southern and Northern sky respectively, as well as the one and only convincing constrain on the distance of Complex A which is in the range of 4~10kpc from the Galactic center.The debatable origins of HVCs mainly for tow reasons, one is that, though the large structure is well understood the gas process is very complicated, the other reason is that HVC is very difficult to be observed for it do not have any emission lines. Therefore the studies of the cold gas are very important and interesting for the galaxy formation and evolution. Because clod gas must make contribution to the QSO absorption lines, we make a semi-analytical model of galaxy which contains galaxy disc (for spiral glalaxy), halo (cold gas cloud surrounded by hot gas) and satellite galaxies to model QSO absorption line systems. First wemodel the spectra of MgII (2796 A) lines and compare with the observations, and we find our model is reasonable in many aspects. Then we use thismodel to study the other two low ionized gas SiII (1260 A) and FeII (2600A) absorption lines, and give some very useful properties. At last we usethis model to study the highly ionized OVI(1032A) absorption lines, and give the modeling spectra of single cloud and the whole galaxy. We find it is reasonable to believe that the cold clouds in the halo and the satellite galaxies cloud be HVCs and can explain their origins by the comparison of different absorption spectra of low and highly ionized gas.